Zoology exam two

Parthengenesis

having involuntary tendency toward or away from light

Why is bilateral symmetry of adaptive value for actively motile animals?

Bilateral symmetry is an important adaptation for actively motile animals because it allows the organism to have the most efficient directional movement. By having both elongated halves of the organism aid in movement, balance and equal proportions are achieved which in turn makes the organisms easier to propel.

Clonorchis sinensis (liver fluke)

snail

Taenia saginata (Tape worm)

snail and fish

Schistosoma japonicum (Blood fluke)

Cow

What is a chaetognath? How do chaetognaths feed?

A chaetognath is an arrow worm. The phylum Chaetognatha are all marine animals and most are highly specialized for their planktonic existence. The name Chaetognatha denotes the sickle-shaped bristles on each side of their mouth. This is not a large group; there are about 130 known species. Their small, straight bodies resemble miniature torpedoes, or darts, ranging from less than 1 to about 12 cm in length.Chaetognaths feed by using vibrations of the sensory bristles to detect prey. Beneath their head, there is a large depression, called a vestibule, leading to the mouth. The vestibule contains teeth and is flanked on both sides by curved chitinous spines used in seizing prey. A pair of eyes is located dorsally. A peculiar hood formed from a fold of the neck can be drawn forward over the head and spines. When a chaetognath captures prey, it retracts its hood, and its teeth and raptorial spines spread apart and then snap shut with startling speed. Chaetognaths are voracious predators, living on planktonic forms, especially copepods, but including a variety of other planktonic crustaceans, small fish, and even other chaetognaths.

What is a trochophore? List and discuss the taxa that have a trochophore and taxa that have something that resembles a trochophore.

A trochophore is a free-swimming ciliated marine larva characteristic of most molluscs and certain ectoprocts, brachiopods, and marine worms. A trochopohore has an ovoid or pyriform body with a preoral circlet of cilia and sometimes a secondary circlet behind the mouth. The taxa that have a trochophore are molluscs and annelids. Trochophores characterize molluscs and annelids exhibiting the ancestral embryonic development pattern and are usually considered homologous between the two phyla. Taxa that have something that resembles a trochophore usually characterizes marine turbellarians, nemertines, brachiopods, phoronids, sipunculids, and echiurids.

What is an Acanthocephalan? How do acanthocephalans get food?

Acanthocephalans are spiny-headed worms characterized by a cylindrical, invaginable proboscis bearing rows or recurved spines, by which it attaches itself to the intestine of its host. All acanthocephalans are endoparasitic, living as adults in the intestine of vertebrates. Various species range in size from less than 2 mm to more than 1 m in length. Females of a species are usually larger than males. Their body is usually bilaterally flattened, with numerous transverse wrinkles. Worms are typically cream colored but may absorb yellow or brown pigments from the intestinal contents.Acanthocephalans have no digestive tract, so acanthocephalans get food by absorbing all their nutrients through their tegument. They can absorb various molecules by specific membrane-transport mechanisms, and other substances can cross the tegumental membrane by pinocytosis. Their tegument bears some enzymes, such as peptidases, which can cleave several dipeptides, and the amino acids are then absorbed by the worm. Like cestodes, acanthocephalans require host dietary carbohydrate, but their mechanism for absorption of glucose is different. As glucose is absorbed, it is rapidly phosphorylated and compartmentalized, forming a metabolic "sink" into which glucose from the surrounding medium can flow. Glucose diffuses down the concentration gradient into the worm because it is constantly removed as soon as it enters.

What is an entoproct? What is an ectoproct? How do the two differ?

An entoproct is a tiny, sessile animal that superficially resembles hydroid cnidarians but has ciliated tentacles that tend to roll inward. Entoprocts have an anus that is located inside the tentacular crown. Most entoprocts are microscopic, and no entoproct is more than 5 mm long. They may be solitary or colonial, but all are stalked and sessile. All are ciliary feeders. With the exception of Urnatella, which occurs in freshwater, all entoprocts are marine forms that have a wide distribution from polar regions to tropics. Most marine species are restricted to coastal and brackish waters and often grow on shells and algae. Entoprocts have a well-developed nerve ganglion that occurs on the ventral side of the stomach, and the body surface bears sensory bristles and pits. Circulatory and respiratory organs are absent. Some species are dioecious, but many are monoecious, most often protandrous hermaphrodites, where the gonad at first produces sperm and later eggs. Colonial forms may have monoecious or dioecious zooids, and colonies can even contain zooids of both sexes. The gonoducts open within the circle of tentacles.Ectoprocta contains aquatic animals that often encrust hard surfaces. Ectoprocts are mostly sessile species, but some slide slowly, and others crawl actively across the surfaces they inhabit. Ectoprocts have an anus that is located outside the circle of tentacles. With very few exceptions, they are colony builders. Each member of a colony is small, typically less than 0.5 mm. Each member of a colony lives in a tiny chamber, called a zoecium, which is secreted by its epidermis. Each zooid consists of a feeding polypide and a case-forming cystid. A polypide includes the lonophore, digestive tract, muscles, and nerve centers. A cystid includes the body wall of an animal, together with its secreted exoskeleton or zoecium. There are about 4,500 living species of ectoprocts. They occupy both freshwater and marine habitats but largely live in shallow waters. Ectoprocts have long been called bryozoans, or moss animals. Ectoprocts have a complete gut and absent respiratory, vascular, and excretory organs. Gaseous exchange is through the body surface, and since ectoprocts are small, coelomic fluid is adequate for internal transport. A ganglionic mass and a nerve ring surround the pharynx, but no specialized sense organs are present in ectoprocts. Most ectoprocts are hermaphroditic. Each colony begins from this single metamorphosed primary zooid, which is called an ancestrula. The ancestrula then undergoes asexual budding to produce the many zooids of a colony. Freshwater ectoprocts have another type of budding that produces statoblasts, which are hard, resistant capsules containing a mass of germinative cells. Statoblasts form during summer and fall. When a colony dies in late autumn, statoblasts remain, and in spring they give rise to new polypides and eventually new colonies.Entoprocts and ectoprocts differ because entoprocts have their anus located within the tentacular crown, while ectoprocts (and other lophophorates), have their anus outside the circle of tentacles. Another difference between entoprocts and ectoprocts is that entoprocts live from the intertidal to depths of 500 meters, whereas ectoprocts largely live in shallow waters. Other differences between entoprocts and ectoprocts are that ectoprocts are true coelomates, and entoprocts have a cup-shaped body with a tentacular ring.

Define Bilateria, Triploblastic, Acoelomate, Cephalization, Protonephridia, Hermaphroditic.

Bilateria: organisms with bilateral symmetry (having a left and a right side that are mirror images)Triploblastic: a body derived from three embryonic cell layers (ectoderm, mesoderm, and endoderm)Acoelomate: an organism that lacks a cavity between the body wall and the digestive tract (no coelom)Cephalization: concentration of sense organs, like the nervous system, at anterior end of the body forming a defined head regionProtonephridia: early osmoregulatory system, hollow cell in the excretory system of certain invertebrates that contains rapidly beating cilia that aid in propelling waste products into excretory tubulesHermaphroditic: organism that produce functional male and female reproductive organs

How do the valves of the brachiopods compare with the valves of bivalve molluscs?

Bivalves are laterally compressed and their two shells (valves) are held together dorsally by a hinge ligament that causes the valves to gape ventrally. The valves are drawn together by adductor muscles that work in opposition to the hinge ligament. The umbo is the oldest part of the shell, and growth occurs in circular lines around it. Externally, brachiopods resemble bivalved molluscs in having two calcareous shell valves that are secreted by a mantle. Brachiopods, however, have dorsal and ventral valves instead of right and left lateral valves as bivalve molluscs do. Unlike bivalves, most of them are attached to a substrate either directly or by means of a fleshy stalk called a pedicel. In most brachiopods, the ventral (pedicel) valve is slightly larger than the dorsal (branchial) valve, and one end projects in the form of a short, pointed beak perforated where the fleshy stalk passes through the shell to attach to the substratum. In many Brachiopods, the pedicel valve is shaped like a classical oil lamp, leading brachiopods to be called "lamp shells".

Define Key Words: cephalized, phototactic, parenchyma, acoelomate, cysticercus, definitive host, intermediate host, miracidia, sporocysts, rediae, cercariae, metacercariae, pseudocoelomate, dioecious, and parthenogenesis

Cephalized: concentration of sense organs, like the nervous system, at the anterior end of the body forming a head and brainPhototactic: movement of an organism toward or away from a source of lightParenchyma: cellular tissue found between the body wall and the organs of invertebrates lacking a coelomAcoelomate: any organism that lacks a cavity between the body wall and the digestive tract (no coelom)Cysticercus: larval tapeworm at a stage in which the scolex is inverted in a sac, found encysted in the muscle tissue of the hostDefinitive Host: an organism which supports the adult and sexually reproductive form of a parasiteIntermediate Host: an organism that supports the immature and nonreproductive forms of a parasiteMiracidia: free-swimming ciliated larval stage in which a parasitic fluke passes from the egg to its first host (like a snail)Sporocysts: a parasitic fluke in the initial stage of infection in a snail host, developed from a miracidiumRediae: larva produced in the sporocyst that can give rise to more rediae or cercariaeCercariae: free-swimming larval stage in which a parasitic fluke passes from an intermediate host (like a snail) to another intermediate host or to the final vertebrate hostMetacercariae: tailless, encysted larva that is usually infects the definitive hostPseudocoelomate: organism with body cavity (true coelom) that is not derived from the mesodermDioecious: an organism that has both male and female reproductive organs in separate individualsParthenogenesis: process of reproduction in which an embryo develops from an unfertilized egg cell

Describe how cephalopods swim and how they eat. Describe adaptations in the circulatory and neurosensory systems of cephalopods that are particularly valuable for actively swimming, predaceous animals.

Cephalopods swim by forcefully expelling water from the mantle cavity througha ventral funnel or siphon - a sort of jet propulsion. The funnel is mobile and can bepointed forwards or backwards to control direction. The force of water expulsion controls the speed. Cephalopods eat by searching for, sensing, and then capturing/grasping their prey with their tentacles, before drawing their prey into their beaklike mouths.The adaptation in the circulatory system of cephalopods that are particularly valuable for actively swimming, predaceous animals is the development of accessory or branchial hearts. These accessory or branchial hearts, located at the base of each gill, increase the pressure of blood going through the capillaries. This allows enough water to be circulated for the cephalopods' high oxygen requirements, and thus allows cephalopods to get enough oxygen into their muscles to be able to efficiently swim. One adaptation in the neurosensory system of cephalopods that is particularly valuable for actively swimming, predaceous animals is that the nervous and sensory systems are more elaborate in cephalopods than in other molluscs because their brain consists of several lobes with millions of nerve cells. Thus, the giant nerve fibers are activated when the animal is alarmed and initiate maximal contractions of the mantle muscles for a speedy escape. Another adaptation in the neurosensory system of cephalopods that is valuable for actively swimming, predaceous animals is that their sense organs are well developed. Except for Nautilus, the other cephalopods have highly complex eyes with cornea, lens, chamber, and retina. The orientation of the eyes is controlled by the statocysts, which are larger and more complex than in other molluscs. The eyes are held in a constant relation to gravity, so that the slit-shaped pupils are always in a horizontal position. Cephalopods have excellent eyesight. Cephalopods can also be taught to discriminate between shapes and are able to remember this discrimination for a considerable amount of time.

Define Key Words: cocoon, segmentation, and metamerism

Cocoon is a protective covering of the developmental stage for the embryos of organisms such as the protective covering in the development embryos of some annelids.Segmentation is the division of the body into segments which are identical in early development, but later activate different genes.Metamerism is specifically serial segmentation where the body is composed of serially repeated parts.

Define the following: ctenidia, odontophore, periostracum, prismatic layer, macreous layer, metanephridia, nephrostome, trochophore, veliger, glochidium, osphradium.

Ctenidia are comblike structures, especially gills of molluscs. An odontophore is a tooth-bearing organ in molluscs, including the radula, radular sac, muscles, and cartilages. Periostracum is the outer layer of a mollusc shell. The prismatic layer is the middle layer of the shell of a mollusk. It is composed of densely packed prisms of calcium carbonate (either aragonite or calcite) laid down in a protein matrix. It is secreted by the glandular margin of the mantle, and an increase in shell size occurs at the shell margin as the animal grows. The nacreous layer is the innermost layer of the shell of a mollusk. It is the layer that lies next to the mantle and is secreted continuously by the mantle surface, so that it increases in thickness during the life of the animal. Very thin and wavy layers produce the iridescent mother-of-pearl found in abalones, chambered nautiluses, and many bivalves. Metanephridia are a type of tubular nephridium with the inner open end draining the coelom and the outer open end discharging to the exterior. A nephrostome is the ciliated, funnel-shaped opening of a nephridium. Trochophore is the free-swimming ciliated marine larva characteristic of most molluscs and certain ectoprocts, brachiopods, and marine worms. Trochophore is also an ovoid or pyriform body with a preoral circlet of cilia and sometimes a secondary circlet behind the mouth. Veliger is the larval form of certain molluscs. It develops from the trochophore and has the beginning of a foot, mantle, and shell. Glochidium is a bivalved larval stage of freshwater mussels. An osphradium is a chemoreceptive sense organ in aquatic snails and bivalves that tests incoming water.

What is hirudin? What animals produce it? How are similar compounds used in medicine?

Hirudin is a naturally occurring peptide in the salivary glands of blood-sucking leeches. Hirudin has a blood anticoagulant property. The animals that produce hirudin are leeches. True bloodsuckers, which include the so-called medicinal leech, Hirundo medicinalis, have cutting plates or chitinous "jaws" for cutting through tough skin. Their salivary glands secrete an anesthetic, as well as anticoagulant enzymes. Similar compounds are used in medicine to help facilitate blood clotting during and after surgeries.

Members of such a large and diverse phylum as Mollusca impact humans in many ways. Discuss this statement.

Humans use molluscs in a variety of ways. Molluscs shells are used in jewelry, buttons, and decoration throughout the world. Pearls are another important product of the bivalves of molluscs. The most common use of molluscs though is as a source of food. Humans regularly eat clams, oysters, scallops, mussels, snails, abalone, squids, and octopi, which all are part of the phylum Mollusca. Members of the phylum Mollusca can also negatively impact humans because they can act as pests, due to the damage they cause. For example, burrowing shipworms do great damage to wooden ships and wharves. Snails and slugs often frequently damage gardens and other green areas. Snails also serve as intermediate hosts for serious parasites of humans and domestic animals.

Compare the main features of each of the following in each class of annelids: circulatory system, nervous system, excretory system.

In organisms of the phylum Annelida, the circulatory system is closed, meaning that blood circulation takes place only within specialized vessels. The muscular blood vessels and aortic arches ("hearts") are used for pumping blood. Respiratory pigments (such as hemoglobin, hemerythrin, or chlorocruorin) are often present. There are amebocytes in the blood plasm. The nervous system of annelids has a double ventral nerve cord and a pair of ganglia with lateral nerves in each segment. Their brain is a pair of dorsal cerebral ganglia with connectives to the ventral nerve cord. In each segment (metamere) of the organism, a pair of complete excretory structures called the metanephridium exists. The metanephridium has an extremity, the nephrostome, which collects waste from the coelom, filtering it and causing reabsorption along its extension (similar to human nephron tubules). The material to be excreted goes out through a pore, the nephridiopore, which opens to the surface of the body.

Contrast the typical life cycle of a monogenean with that of a digenetic trematode.

Monogeneans have a single host life cycle and live on the outside of their host (ectoparasites) while digenetic trematodes have a several host life cycle and live within their hosts (endoparasites). The life cycle of a monogenean begins when adults lay their eggs in water and free-swimming larva hatch. These juveniles attach to one host and once they reach adulthood they will lay eggs and repeat the cycle. The digenetic trematode life cycle begins when adults lay eggs which are then ingested and hatched through bird feces. Trematodes go through many stages during their life cycle starting as eggs found in an intermediate host like a snail. They then become miracidium, then sporocysts, then rediae, then cercariae, metacercaria and finally mature adult flukes which can then lay eggs of their own once inside the final host and repeat the cycle.

Briefly describe how a typical bivalve feeds and how it burrows.

Most bivalves are filter feeders. Respiratory currents bring both oxygen and organic materials to the gills, where ciliary tracts direct currents to the tiny pores of the gills. Gland cells on the gills and labial palps secrete copious amounts of mucus, which entangles particles suspended in water going through gill pores. These mucous masses then slide down the outside of the gills toward food grooves at the lower edge of the gills. Heavier particles of sediment fall from the ctenidia, but smaller particles travel along the food grooves toward the labial palps. Since the palps are grooved and ciliated, they sort the particles and direct tasty ones encased in the mucous mass into the mouth. Also, most bivalves have a cylindrical style sac opening into the stomach that secretes a gelatinous rod called a crystalline style. The crystalline style projects into the stomach and is kept whirling by means of cilia in the style sac. The rotation of the style helps to dissolve its surface layers, freeing digestive enzymes that it contains, and rolling the mucous food mass.Many bivalves can burrow into mud or sand, but some have evolved a mechanism for burrowing into much harder substances, such as wood or stone. Shipworms have a long, wormlike appearance and a pair of slender posterior siphons that keep water flowing over the gills. They also have a pair of small globular valves on the anterior end with which they burrow. The valves have microscopic teeth that function as very effective wood rasps. The animals extend their burrows with a rasping motion of the valves. This motion sends a continuous flow of fine wood particles into the digestive tract, where they are attacked by cellulase produced by symbiotic bacteria. Some clams also bore into rock. The piddock (Pholas) bores into limestone, shale, sandstone, and sometimes wood or peat. It has strong valves that bear spines, which it uses to cut away the rock gradually, while anchoring itself with its foot.

Discuss the evolution of bivalve gills. Compare bivalve gills with the gills of other molluscs. Include a description of protobranch and lamellibranch gills along with a discussion of morphology, primary, and secondary functions.

Most bivalves have gills that are highly modified for filter-feeding. Their gills are derived from primitive ctenidia by a great lengthening of filaments on each side of the central axis. As ends of long filaments became folded back toward the central axis, ctenidial filaments developed a somewhat elongated W shape. Then, filaments lying beside each other became joined by ciliary junctions or tissue fusions, forming platelike lamellae with several vertical water tubes inside. So, by a great lengthening of individual gill filaments, ctenidia became adapted for filter-feeding and separated the incurrent chamber from the excurrent, suprabranchial chamber. Respiration in most gastropods is performed by ctenidium. After some prosobranchs lost one gill, most lost half of the other gill and the central axis attached to the wall of the mantle cavity. They acquired the most efficient gill arrangement by circulating water in one side and out the other. Protobranch gills are primarily used for respiration. The protobranch gills are paired structures lying at an oblique angle on either side of the body in the posterior region of the mantle cavity. General bivalves have a lamellibranch gill that is used for both respiration and feeding. It produces a mucus that covers the gills, catching particles out of the water.

Compare and contrast the morphology of a Nautilus and a snail.

Nautilus is a cephalopod. Nautilus have a shell that is divided by transverse septa into internal gas chambers. Nautilus has a siphon that is used for movement. Nautilus also have a closed circulatory system. A snail is a gastropod. A snail's shell houses internal organs. Snails move using their foot. Snails have an open circulatory system. Both a Nautilus and a snail have coiled shells, simple eyes, tentacles, and radula.

Describe the layers of a mollusc shell.

Most of the time, molluscs have three layers: the periostracum, the prismatic layer, and the nacreous layer. The periostracum is the outer organic layer that is composed of an organic substance called conchiolin, which consists of quinone-tanned protein. It helps to protect underlying calcareous layers from erosion by boring organisms. It is secreted by a fold of the mantle edge, and growth occurs only at the margin of the shell. On the older parts of the shell, periostracum often becomes worn away. The prismatic layer, which is the middle layer, is composed of densely packed prisms of calcium carbonate (either aragonite or calcite) that is laid down in a protein matrix. It is secreted by the glandular margin of the mantle, and an increase in shell size occurs at the shell margin as the animal grows. The nacreous layer of the mollusc shell, the innermost layer, is the layer of the shell that lies next to the mantle and is secreted continuously by the mantle surface (so that it increases in thickness during the life of the animal). The calcareous nacre is laid down in thin layers. The very thin and wavy layers are what produces the iridescent mother-of-pearl found in abalones (Haliotis), chambered nautiluses (Nautilus), and many bivalves.

Give three differences between nemerteans and platyhelminths.

One difference between nemerteans and platyhelminths is that nemerteans have a complete digestive system (mouth to anus), whereas platyhelminths have an incomplete gut that may be branched. The gut is absent in cestodes. A second difference between nemerteans and platyhelminths is that nemerteans have an eversible proboscis (which lies free in a cavity above the alimentary canal) and its sheath, for which there are no counterparts within any other phylum; platyhelminths do not have an eversible proboscis and its sheath. Platyhelminths have no clear defining feature. A third difference between nemerteans and platyhelminths is seen within their reproductive system. Nemerteans are mostly dioecious. Platyhelminths are mostly monoecious (hermaphrodites).

Describe three ways that various polychaetes obtain food.

One way that various polychaetes obtain food is by seizing food with their chitinous jaws. They protrude their jaws through the mouth when they evert their pharynx. Clam worms obtain food this way. Food is then swallowed as the worm withdraws its pharynx. The food then moves through the alimentary canal by peristalsis. A second way that various polychaetes obtain food is by feeding on particles. Tubeworms, for example, use cilia or mucus to obtain food, typically plankton and detritus. Tubeworms (some which are ciliary feeders) feed on suspended particles, and they may have a crown of tentacles that can be opened like a fan or withdrawn into the tube. Other tubeworms are deposit feeders, and they obtain food by collecting particles on or in the sediments. Some deposit feeders like Amphitrite protrude their heads above the mud and extend long tentacles over the surface to find food. Cilia and mucus on the tentacles entrap particles found on the sea bottom and move them toward the mouth. A third way that various polychaetes, such as fanworms, obtain food is by using ciliary action to draw food down to the feathery arms or radioles. This food drawn to the feather arms by ciliary action is trapped in mucus and carried down ciliated food grooves to the mouth. Particles too large for the food grooves pass along the margins of the food grooves and fall away before they reach the mouth. Only small particles of food enter the mouth. Sand grains are stored in a sac to be used later in enlarging the tube.

Distinguish between opisthobranchs and pulmonates.

Opisthobranchs and pulmonates are two of the major groups of Gastropods. Opisthobranchs include a wide variety of molluscs that include sea slugs, sea hares, sea butterflies, and bubble shells. Nearly all opithobranchs are marine, and most of them are shallow-water forms that hide under stones and seaweed. A few opisthobranchs are pelagic. There are currently nine or more orders of opisthobranchs that are recognized. Opisthobranchs show partial or complete detorsion, and because of this, their anus and gill (if present) are displaced to the right side or rear of the body. Most opisthobranchs have two pairs of tentacles, with the second pair of tentacles being further modified with platelike folds that increase the area for chemoreception. Their shell is typically reduced or absent. All opisthobranchs are monoecious.Pulmonates include land and most freshwater snails and slugs, along with a few brackish and saltwater forms. Pulmonates have lost their ancestral ctenidia, but their vascularized mantle wall becomes a lung which fills with air by contraction of the mantle floor; some aquatic species develop secondary gills in the mantle cavity. The anus and nephridiopore open near the pneumostome, and waste is expelled forcibly with air or water from the lung. Pulmonates show some detorsion. They are also monoecious. Aquatic pulmonates have one pair of nonretractile tentacles, at the base of which are eyes. Land pulmonates have two pairs of tentacles, with the posterior pair bearing eyes.

Describe the phylum Cycliophora. How many species are described and when was the first species described? Where does it live? What does it eat? What is meant by a dwarf parasitic male?

Organisms in the phylum Cycliophora have a body plan that is relatively simple. The mouth leads into a U-shaped gut ending with an anus that opens outside the ciliated ring. The body is acoelomate. The epidermis is cellular and surrounded by a cuticle. The life cycle has sexual and asexual phases. So far, three species have been described. The first species was described in December of 1995, when P. Funch and R. M. Kristensen reported their discovery of some very strange little creatures clinging to the mouthparts of the Norway lobsters. The animals were tiny, only 0.35 mm long and 0.10 mm wide, and they did not fit into any known phylum. They were named Symbion pandora, the first members of the phylum Cycliophora. Cycliophorans have a very specialized habitat: they live on mouthparts of marine decapod crustaceans in the Northern Hemisphere. They attach to bristles on the mouthparts with an adhesive disc on the end of an acellular stalk. They feed by collecting bacteria, or bits of food dropped from their lobster host, on a ring of compound cilia that surrounds the mouth.Males are not produced directly by the feeding stage, as previously thought, but instead arise as a distinct individual from budding cells inside an intermediate stage named the Prometheus larva. The dwarf parasitic male is the ciliated, sexually mature stage. The budding cells inside the attached Prometheus larva usually develop two internal dwarf males. Each dwarf male is heavily ciliated and has a well‐developed nervous system with a relatively large brain, numerous gland and muscle cells, testis with bundles of sperm, and one penial structure. The dwarf male is freed from the attached Prometheus larva.

Define the following words: parenchyma, proglottid, acoelomate, eucoelomate, triploblastic, diploblastic, cercaria, sporocyst, scolex, opisthaptor, miracidium, and flame cells.

Parenchyma: cellular tissue between the body wall and the organs of invertebrate animals lacking a coelomProglottid: an individual segment in the strobila of a tapeworm, contains both male and female mature reproductive systemsAcoelomate: invertebrate that lacks a fluid filled body cavity between body wall and internal organs (no coelom)Eucoelomate: organisms that has a true fluid filled body cavity that attaches to organs (true coelom)Triploblastic: a body derived from three embryonic cell layers (ectoderm, mesoderm, and endoderm)Diploblastic: a body derived from two embryonic cell layers (ectoderm and endoderm)Cercaria: third stage, free-swimming larval stage of parasitic flukes, passes from an intermediate host (like a snail) to another intermediate host or to the final vertebrate hostSporocyst: second stage, a parasitic fluke in the initial stage of infection in a snail host, developed from a miracidiumScolex: anterior end of a tapeworm, has both suckers and hooks for attachmentOpisthaptor: large, complex posterior with adhesive organs found in monogenetic trematodeMiracidium: first stage, free-swimming ciliated larval stage in which a parasitic fluke passes from the egg to its first host (snail)Flame Cells: specialized excretory cell found in the simplest freshwater invertebrates

What characteristics of phylum Annelida distinguish it from other phyla?

Phylum Annelida experience metamerism (segmentation), and metamerism is seen in only two other animal phyla. Their coelom is also highly developed, and this, together with the septal arrangement of fluid-filled compartments and a well-developed body-wall musculature, is an effective hydrostatic skeleton for precise burrowing and swimming movements. Annelids, with the exception of leeches, bear tiny bristles called setae that help anchor segments during locomotion. Annelids also tend to have a more centralized nervous system.

Compare and contrast the features of the following phyla; Phronida, Ectoprocta, and Brachiopoda.

Phylum Phoronida are small, wormlike animals that mostly live on the substrate below shallow coastal waters. They range from a few millimeters to 30 cm in length. Each worm secretes a leathery or chitinous tube in which it lies free, but which it never leaves. They thrust out the tentacles on the lophophore for feeding, but a disturbed animal can withdraw completely into its tube. Cilia on the tentacles direct a water current toward a groove between the two ridges, which leads toward the mouth. Phoronids have an extensive system of contractile blood vessels in a functionally, but not technically, closed circulatory system. They have no heart. Their blood contains hemoglobin within nucleated cells. There is a pair of metanephridia. A nerve ring sends nerves to tentacles and the body wall, but the system is diffuse and lacks a distinct ganglion that could be called a brain. A single giant motor fiber lies in the epidermis, and an epidermal nerve plexus supplies the body wall and epidermis. There are both monoecious (the majority) and dioecious species of Phoronida, and at least two species reproduce asexually. Fertilization may be internal or external, but contrary to early reports, cleavage is radial.Phylum Ectoprocta are aquatic animals that often encrust hard surfaces. Ectoprocts are mostly sessile species, but some slide slowly, and others crawl actively across the surfaces they inhabit. Ectoprocts have an anus that is located outside the circle of tentacles. With very few exceptions, they are colony builders. Each member of a colony is small, typically less than 0.5 mm. Each member of a colony lives in a tiny chamber, called a zoecium which is secreted by its epidermis. Each zooid consists of a feeding polypide and a case-forming cystid. A polypide includes the lophophore, digestive tract, muscles, and nerve centers. A cystid includes the body wall of an animal, together with its secreted exoskeleton or zoecium. Ectoprocts have long been called bryozoans, or moss animals. Ectoprocts have a complete gut and absent respiratory, vascular, and excretory organs. Gaseous exchange is through the body surface, and since ectoprocts are small, coelomic fluid is adequate for internal transport. A ganglionic mass and a nerve ring surround the pharynx, but no specialized sense organs are present in ectoprocts. Most ectoprocts are hermaphroditic. Cleavage is radial but apparently mosaic. Each colony begins from this single metamorphosed primary zooid, which is called an ancestrula. The ancestrula then undergoes asexual budding to produce the many zooids of a colony. Freshwater ectoprocts have another type of budding that produces statoblasts, which are hard, resistant capsules containing a mass of germinative cells. Statoblasts form during summer and fall. When a colony dies in late autumn, statoblasts remain, and in spring they give rise to new polypides and eventually new colonies.Phylum Brachiopoda are attached, bottom-dwelling, marine forms that mostly prefer shallow water, although they occur at nearly all ocean depths. Brachiopoda, or lamp shells, are an ancient group. Brachiopods have dorsal and ventral valves. Most brachiopods are attached to a substrate either directly or by means of a fleshy stalk called a pedicel. Muscles both open and close the valves and provide movement for the stalk and tentacles. Their body occupies only the posterior part of the space between the valves, and extensions of the body wall form mantle lobes that line and secrete the shell. Their long horseshoe shaped lophophore in the anterior mantle cavity bears long, ciliated tentacles used in respiration and feeding. A brachiopod's lophophore not only creates food currents, as it does in other lophophorates, but also seems to absorb dissolved nutrients directly from environmental seawater. They have three coelomic cavities, called the protocoel, mesocoel, and metacoel. One or two pairs of nephridia open into the coelom and empty into the mantle cavity. Brachipoda have an open circulatory system with a contractile heart. The lophophore and mantle are probably the chief sites of gaseous exchange. There is a nerve ring with a small dorsal and a larger ventral ganglion. Most species have separate sexes, and temporary gonads discharge gametes through the nephridia. Most fertilization is external, but a few species brood their eggs and young. Cleavage is radial. Phoronida, Ectoprocta, and Brachiopoda are all similar in the sense that they all have a lophophore, all have a nerve ring, all have a coelom, and all have cleavage that is radial. or Phronida: small marine animals, sessile with minimal movement capabilities, occupy a leathery or chitinous cylindrical tube of their own secretions for protection, colonial, buried vertically in soft sediments, live in shallow marine waters, have a horseshoe shape lophophore with ciliated tentacles for feeding and forming water currents, u-shaped gut, anus located outside of lophophoreEctoprocta: marine and freshwater invertebrates, sessile with minimal movement capabilities, form colonies of zooids, found in shallow water, colonies produced asexually and sexually, anus outside the circle of tentacles, horseshoe shaped lophophore with cilia which will generate the current, retractable tentacles, gut is U-shapedBrachiopoda: commonly called lamp shells, solitary, marine and found in benthic and shallow areas, enclosed in pair of dorsal ventrally oriented valves, sessile and attached to substrates by fleshy pedicle, large lophophore that is horseshoe-shaped used for filter feedingPhoronida, Ectoprocta, and Brachiopoda all share horseshoe-shaped lophophores, their aquatic nature and preference for shallow waters, have an anus located outside of tentacles, and most of these organisms are sessile.

What do planarians (triclad flatworms) eat, and how do they digest it?

Planarians are carnivores and have muscular mouths in which they consume living, or even dead, material. Some common organisms which planarians prey upon are small crustaceans, protozoans, nematodes, and rotifers. Planaria digest using both extracellular and intracellular digestion. In extracellular digestion, food passes through the mouth it travels down the pharynx and into the intestines. In the intestines proteolytic enzymes break down the food. In intracellular digestion, food particles are sucked into the intestines where phagocytic cells complete digestion.

Contrast the body structure and life cycle of a planarian and a tapeworm.

Planarians' body structure is free-living with soft flattened bodies covered with ciliated epidermis secreting cells and rodlike bodies (rhabdites). Their mouth is on a ventral surface, sometimes near the center of the body, and they have no body cavity except intercellular lacunae in parenchyma. Their protonephridian have flame cells, and they have ocelli. They also have one ventral pair of longitudinal nerve cords, which form a ladder-like pattern. Planarians have a life cycle where they can reproduce sexually and asexually by fission; planarians are mostly hermaphroditic, but some have asexual fission. Freshwater planarians merely constrict behind the pharynx and separate into two animals, each of which regenerates the missing partsTapeworms usually have long, flat bodies composed of a scolex, for attachment to the host, followed by a linear series of reproductive units or proglottids. They have a scolex, or holdfast, that is usually provided with suckers or suckerlike organs and often with hooks or spiny tentacles as well. Tapeworms entirely lack a digestive system, but they do have well-developed muscles, and their excretory system and nervous system are somewhat similar to those of other flatworms. They have no special sense organs, but they do have sensory endings in the tegument that are modified cilia. Tapeworms have no external, motile cilia that occur in adults, and their tegument is of a distal cytoplasm with sunken cell bodies beneath the superficial muscle layer. Adult tapeworm bodies are covered with noncilliated syntical tegument. The entire surface of tapeworms is covered with minute projections similar to microvilli of the vertebrate small intestine. These microtriches greatly enlarge the surface area of the tegument, which is a vital adaptation for a tapeworm since it must absorb all its nutrients across its tegument. The main body of tapeworms, the chain of proglottids, is called a strobila. Typically, there is a germinative zone just behind the scolex where new proglottids are formed. The tapeworm body is unusual because of the absence of many typical landmarks. Tapeworms have no head, and the scolex, used for attachment, is a remnant of the posterior part of the ancestral body. Tapeworms have a life cycle where the adults are parasitic in the digestive tract of vertebrates. Tapeworms are usually monoecious. Tapeworms are capable of infecting almost all vertebrate species. Their development is indirect, and tapeworms require at least two hosts; there are rare exceptions to this. Their first host may be a vertebrate or an invertebrate. Often their intermediate host is an invertebrate. Normally, adult tapeworms do little harm to their hosts.

Discuss a cladogram showing a proposed phylogeny of the following taxa; Opisthobranchia, Nautiloidea, Monoplacophora, Prosobranchia, Bivalvia, Coleoidea, Pulmonata, Scaphopoda, and Polyplacophora. Make sure to include characters between each node.

Polyplacophora, Monoplacophora, Bivalvia, and Scaphopoda are all classes of the phylum Mollusca. Prosobranchia, Opisthobranchia, and Pulmonata are all subclasses of the class Gastropoda of the Phylum Mollusca. Nautiloidea and Coleoidea are two of the subclasses (along with the entirely extinct Ammonoidea) of the class Cephalopoda of the Phylum Mollusca. Polyplacophora have a shell with 7-8 plates, a mantle cavity that is extended along sides of the foot, and multiple gills. Monoplacophora have a univalve, caplike shell, and serial repetition of soft parts. Bivalvia do not have a head, they have loss of radula, they have byssus, they have a bivalve shell, and they have lateral compression of their body. Scaphopoda have a reduced head, captacula, loss of gills, and a tusk-shaped, open-ended shell. The three subclasses of the class Gastropoda (Prosobranchia, Opisthobranchia, and Pulmonata) are characterized by experiencing torsion and having a concentration of visceral mass. Nautiloidea and Coleoidea (Cephalopoda) are characterized by having siphuncles, beaklike jaws, arms/tentacles, a septate shell, and a closed circulatory system.

What is progenesis? How does this relate to the phylogeny of platyhelminths? How does this view compare to the planoid theory discussed by Libby Hymen? Discuss two competing hypotheses for the origin of the body cavity. How does Lobatocerebrum inform this debate? Recent evidence suggest that members of Acoelomorpha constitute a sister group for all other Bilateria. How do members of this group differ from typical protostomes?

Progenesis is the maturation of gametes in an organism that is still otherwise in the juvenile stage of development. Progenesis relates to the phylogeny of platyhelminths because there are theories that the ancestor of platyhelminths were not acoelomate like flatworms today, but were like a worm with a body cavity. The simplicity of the platyhelminth is a derived feature rather than an ancestral feature. This view compares to the planoid theory discussed by Libby Hymen because Libby Hymen did not think flatworms were progenic, but believed they were simple because they were ancestral. She thought platyhelminths formed the keystone group that sat between protostomes and deuterostomes, and she believed that the ancestors were a worm with a body cavity. One competing hypothesis for the origin of the body cavity is based upon the fact that flatworms are the first ancestor and are protostomes formed by a schizocoely. In the schizocoelous plan, mesodermal cells fill the blastocoel, forming a solid band of tissue around the gut cavity. Then, through programmed cell death, space opens inside the mesodermal band. This new space is a coelom. The embryo has two body cavities, a gut cavity and a coelom. The second competing hypothesis for the origin of the body cavity is based on enterocoely. Enterocoely is the deuterostome way that is homologous back to the cnidarians. In the enterocoelous plan, cells from the central portion of the gut lining begin to grow outward as pouches, expanding into the blastocoel. The expanding pouch walls form a mesodermal ring. As the pouches move outward, they enclose a space. The space becomes a coelomic cavity or coelom. Eventually the pouches pinch off from the gut lining, completely enclosing a coelom bounded by mesoderm on all sides. The embryo has two body cavities, a gut cavity and a coelom. Lobatocerebrum informs this debate because it is an example of the way a body cavity can compress. Lobatocerebrum goes against Libby Hymen's ideas. Lobatocerebrum is also a good example of progenesis. Acoelomorphs differ from typical protostomes because have a distinct anteroposterior axis, but the diffuse collection of nerve cells at the anterior end of the body lacks ganglia typical of a "true" brain. Acoelomorphs also have radial arrangements of nerves in the body, instead of a ladder like pattern seen in platyhelminths. Acoelomorph' statocysts differ in structure from those of platyhelminths. Recently, phylogenetic studies using molecular characters describe acoelomorphs as early diverging, bilaterally symmetrical triploblasts. Acoelomorphs have only 4 or 5 Hox genes, unlike platyhelminths which have seven or eight such genes.

Define each of the following: prostomium, peristomium, pygidium, radioles, parapodium, metanephridia, notopodium, neuropodium, parapodium.

Prostomium is the region of a segmented animal anterior to the mouth. Peristomium is the foremost true segment of an annelid. It bears a mouth. Pygidium is the posterior closure of a segmented animal. It bears the anus. Radioles are featherlike processes from the head of many tubicolous polychaete worms (phylum Annelida), used primarily for feeding. Parapodium is one of the paired lateral processes on each side of most segments in polychaete annelids. The parapodium is variously modified for locomotion, respiration, or feeding. Metanephridia is a type of tubular nephridia with the inner open end draining the coelom and the outer open end discharging to the exterior. Notopodium is a lobe of parapodium nearer the dorsal side in polychaete annelids. Neuropodium is a lobe of parapodium nearer the ventral side in polychaete annelids. Parapodium is one of the paired lateral processes on each side of most segments in polychaete annelids. The parapodium is variously modified for locomotion, respiration, or feeding.

Define Key Words: radula, glochidia, visceral mass

Radula is a rasping tongue found in most molluscs. Glochidia is a bivalved larval stage of freshwater mussels. The visceral mass is the portion of a mollusk body plan containing digestive, circulatory, respiratory, and reproductive organs, and it depends primarily on ciliary tracts for its functioning.

Why is Taenia solium a more dangerous infection than Taenia saginata?

Taenia solium (pork tapeworm) is more dangerous than Taenia saginata (beef tapeworm) because humans are the final host of the adult tapeworm. Taenia solium defecate the fertilized eggs and once hatched the larvae can migrate anywhere in the human body infecting vital nervous tissues like the brain or even the spinal cord. Taenia saginata is less dangerous when a human host is infected because the larvae cannot spread completely throughout the host's body, rather, they spread throughout intestinal tissues.

What is meant by mesoderm from the 4d cell? Which phyla express this pattern? What is meant by a molluscan or annelid cross at the 64 cell stage? Which phyla express which pattern?

The 4-D cell is what forms the mesoderm in protostomes. The 4-D cell is numbered and then given letters as division occurs. The 4-D cell predeceases the mesoderm, which is responsible for the formation of the heart and circulatory system. The mesoderm from the 4-D cell is expressed in Phyla: Brachiopoda, Turbillaria, Nemertea, Annelida, Mollusca, Arthropodia, Phoronids, Ectoprocta, Platyhelminthes, Echiurid, and Chaetognatha.When looking for phylogeny, the embryological process is used to classify organisms using developmental features. When looking at spiral cleaving protostomes at the 64 cell stage, you get either an A (+) shape or an X shape. One is molluscan and one is Annelida. We can then look at other organisms' developmental stages and decide what phylum it is closer to. Sipunculida is closest to Mollusca, whereas Echiurids are closer to Annelida.

Describe the annelid body plan, including body wall, segments, coelom and its compartments, and coelomic lining. Explain how the hydrostatic skeleton of annelids helps them to burrow. How is the efficiency for burrowing increased by segmentation?

The annelid body plan typically has a two-part head, that is composed of a prostomium and a peristomium. Their two part-head is followed by a segmented body and a terminal portion called the pygidium that has an anus. The head and pygidium are not considered to be segments. New segments differentiate during development just in front of the pygidium. The oldest segments are at the anterior end and the youngest segments are at the posterior end. Each of the segments typically contain respiratory, nervous, and excretory structures, along with a coelom. Parapodia may be present on each segment. The coelom develops embryonically as a split in the mesoderm on each side of the gut (schizocoel), forming a pair of coelomic compartments in each segment. Peritoneum lines the body wall of each compartment. Peritoneum is a layer of mesodermal epithelium. The peritoneum forms dorsal and ventral mesenteries that cover all organs. The peritonea of adjacent segments form septa, and the septa are perforated by the gut and longitudinal blood vessels. The body wall surrounds the peritoneum and coelom, and the body wall contains strong circular and longitudinal muscles that are adapted for swimming, crawling, and burrowing.The coelom of most annelids, except for leeches, is filled with fluid and acts as a hydrostatic skeleton. Crawling motions are produced by alternating waves of contraction by longitudinal and circular muscles passing down the body (peristaltic contractions). Circular muscle contractions act on the fluid in the closed coelomic space to make the segment long and thin. On the other hand, when longitudinal muscles contract, the segment becomes shorter and wider. Therefore, forces powerful enough for rapid burrowing (as well as locomotion) can be produced. Septa prevents fluid from moving from one segment to the next, so muscle contractions changes the shape of a segment but not its volume. An annelid (such as an earthworm) is able to use short, wide segments as anchors and extend its body forward from an anchor point by becoming long and thin. The front of the worm then anchors in its new position and the rest of the body is pulled up behind the anchor point. Forward extension begins again. A burrower requires a compartmentalized coelom. Thus, the efficiency for burrowing is increased by segmentation by permitting the independent movement of segments and allowing annelids to contract and expend certain segments.

Briefly describe characteristics of the hypothetical ancestral mollusc, and tell how each class of molluscs differs from the ancestral condition with respect to each of the following: shell, radula, foot, mantle cavity and gills, circulatory system, and head.

The characteristics of the hypothetical ancestral mollusk are that it has present radula, a digestive system that consists of a mouth, digestive gland, a stomach, an intestine, an anus, and a present mantle cavity. The circulatory system consists of the heart. Nerve collar, foot, and retractor muscles are present. The excretory system consists of nephridium. The hypothetical ancestral mollusk also has calcareous spicules, and gills and gonads that are present.The Class Caudofoveata have an absent shell, foot, circulatory system, and head. They have a present radula, mantle cavity, and gills.The Class Solenogastres have an absent shell, radula, mantle cavity, gills, circulatory system, and head. They have a present foot.The Class Polyplacophora have an absent shell. The radula, foot, mantle cavity, gills, circulatory system and head are all present (the head is reduced though).The Class Monoplacophora have an absent mantle cavity, circulatory system, and head. They have a present shell, radula, foot, and gills.The Class Gastropoda have a shell that is present, along with radula, a foot, a mantle cavity, gills, a circulatory system, and a head.The Class Bivalvia have an absent mantle cavity, radula, and head, but they have a present shell, foot, gills, and circulatory system.The Class Scaphopoda have an absent shell, gills, circulatory system, and head. The radula, foot, and mantle cavity are all present.The Class Cephalopoda have an absent mantle cavity and head, but they have a present shell, along with radula, a foot, gills, and a circulatory system.

Describe the function of the clitellum and cocoon.

The clitellum functions in reproduction, where it secretes mucus that is needed to hold the ventral surfaces together. After discharge, sperm travel to seminal receptacles of the other worm via its seminal grooves. After copulation, each worm secretes first a mucous tube and then a tough, chitinlike band that forms a cocoon around its clitellum. The fertilization of eggs then occurs within the cocoon. When the cocoon slips past the anterior end of the worm, its ends close producing a sealed, lemon-shaped body. This cocoon protects the eggs, until they are ready to hatch. Embryogenesis occurs within the cocoon, and the form that hatches from the egg is a young worm similar to the adult. Thus, development is direct with no metamorphosis. Juveniles do not develop a clitellum until they are sexually mature.

Explain the phylogeny of molluscan classes. Make sure to include a feature or two between each branch and node of the cladogram.

The eight molluscan classes are Caudofoveata, Solengastres, Polyplacophora, Monoplacophora, Gastropoda, Bivalvia, Scaphopoda, and Cephalopoda. The class Caudofoveata is characterized by calcareous spicules that form scales. The class Solengastres is characterized by loss of gills, a foot groove, and copulatory spicules at the posterior. Class Polyplacophora is characterized by a shell with 7-8 plates, a mantle cavity extended along sides of the foot, and multiple gills. Class Monoplacophora is characterized by a univalve, caplike shell and series repetition of soft parts. The class Gastropoda is characterized by experiencing torsion and having a concentration of visceral mass. The class Bivalvia is characterized by having a head that is lost, byssus, loss of radula, a bivalve shell, and lateral compression of the body. The class Scaphopoda is characterized by having a reduced head, captacula, loss of gills, and a tusk-shaped, open-ended shell. The class Cephalopoda is characterized by having siphuncles, beaklike jaws, a septate shell, and a closed circulatory system. More generally, the classes Caudofoveata, Solenogastres, and Polyplacophora share the characteristics of having 7 dorsal shell plates and aragonite spicules. The classes Monoplacophora, Gastropoda, Bivalvia, Scaphopoda, and Cephalopoda share the characteristics of having a single, well-defined shell gland, periostracum, prismatic, nacreous layers, a univalve shell, and preoral tentacles. All classes of the phylum Mollusca share a posterior mantle cavity with 1 or more pairs of gills, radula, a chambered heart with atria and ventricles, a muscular foot (or foot precursor), calcareous spicules produced by the mantle shell gland, a mantle, and a reduction of the coelom and development of the hemocoel.

Describe each class of mollusca.

The first class of Mollusca is Class Caudofoveata. Class Caudofoveata are wormlike and have an absent shell, head, and excretory organs. They have radula that is usually present. They have a mantle with a chitinous cuticle and calcareous sclerites. They have an oral pedal shield near their anterior mouth, and they have a mantle cavity at their posterior end with a pair of gills. Sexes are separate in the Class Caudofoveata. The Class Caudofoveata were formerly united with solenogasters in the class Aplacophora. Examples of this class include Chaetoderma and Limifossor.The second class of Mollusca is Class Solenogastres. Organisms in this class are often referred to as solengasters. They are wormlike and have an absent shell, head, and excretory organs. Their radula can be present or absent. Their mantle is usually covered with calcareous sclerites or spicules. They have a rudimentary mantle cavity that is posterior. They do not have true gills, but sometimes they have secondary respiratory structures. Their foot is represented by a long, narrow, ventral pedal groove. They are hermaphroditic. An example of the Class Solenogastres is Neomenia.The third class of Mollusca is Class Polyplacophora (chitons). Their bodies are elongated, and they have a dorsoventrally flattened body with a reduced head. They are bilaterally symmetrical. They do have radula that is present. Their shell consists of seven or eight dorsal plates. Their foot is broad and flat. They have multiple gills along the sides of their body between the foot and mantle edge. The sexes are usually separate in the Class Polyplacophora. They have a trochophore but no veliger larva. Examples of the Class Polyplacophora include Mopalia and Tonicella.The fourth class of Mollusca is Class Monoplacophora. Organisms in Class Monoplacophora have a bilaterally symmetrical body with a broad, flat foot. They have a single, limpetlike shell. Their mantle cavity has three to seven pairs of gills. They have large coelomic cavities and radula that is present. They also have three to seven pairs of nephridia, two of which are gonoducts. They have separate sexes. An example of this class is Neopilina.The fifth class of Mollusca is Class Gastropoda. Organisms in this class are commonly snails and slugs. They have an asymmetrical body that shows effects of torsion. Their body is usually in a coiled shell, although the shell is uncoiled or absent in some. Their head is well-developed, with radula. Their foot is large and flat. They have one or two gills, or they have a mantle that is modified into secondary gills or a lung. Most have a single atrium and single nephridium. They have a nervous system with cerebral, pleural, pedal, and visceral ganglia. They can be dioecious or monoecious, and some have a trochophore, typically with veliger, while some are without pelagic larva. Examples of the Class Gastropoda include Busycon, Polinices, Physa, Helix, and Aplysia.The sixth class of Mollusca is Class Bivalvia (bivalves). Their bodies are enclosed in a two-lobed mantle. They have a shell with two lateral valves of variable size and form, with a dorsal hinge. Their head is greatly reduced, but their mouth has labial palps. They do not have radula. They also have no cephalic eyes, but there are a few organisms in this class that have eyes on the mantle margin. Their foot is usually wedge shaped, and their gills are platelike. Their sexes are usually separate, typically with trochophore and veliger larvae. Examples of the Class Bivalvia include Anodonta, Venus, Tagelus, and Teredo.The seventh class of Mollusca is Class Scaphopoda (tusk shells). Their bodies are enclosed in a one-piece tubular shell that is open at both ends. They have a conical foot. They have a mouth with radula and contractile tentacles (captacula). Their head is absent. They have a mantle for respiration. Their sexes are separate, and they have trochophore larva. An example of the Class Scaphopoda is Dentalium.The eighth class of Mollusca is Class Cephalopoda, which includes squids, cuttlefish, nautilus, and octopuses. Their shell is often reduced or absent. Their head is well developed with eyes and a radula. Their head has arms or tentacles. Their foot is modified into a siphon. They have a nervous system of well-developed ganglia, centralized to form a brain. Sexes are separate, with direct development. Examples of this class include Sepioteuthis, Octopus, and Sepia.

Name and distinguish the taxonomic classes in phylum Platyhelminthes. Describe a cladogram including each of the classes of the phylum Platyhelminthes. Include several characteristics listed at each node.

The four classes of Platyhelminthes are Turbellaria, Trematoda, Monogenea, and Cestoda. Coming first on the cladogram would be Trubellaria distinguished by its free swimming nature. Trematoda, Monogenea, and Cestoda would follow as a clade often called the Neodermata. Trematoda are distinguished by their ventral sucker, Monogenea and Cestoda are distinguished from Trematoda by their posterior attachment organs. Cestoda are distinguished from Monogenea because of their scolex and absent digestive system.Turbellaria are free living and exhibit bilateral symmetry. They can be found in a variety of environments including terrestrial, marine, and freshwater. Turbellaria are unique because they can be nonparasitic and have a ciliated epidermis and rhabdites which are not found in the adult forms of the other classes.Trematoda are parasitic flatworms known as flukes that fall into two subclasses, the Aspidogastrea and Digenea. The intermediate host is usually a snail and the primary host is usually a vertebrates. To aid in their parasitic lifestyle, trematoda are equipped with suckers, hooks, penetration glands, and increased reproductive capacity. They are endoparasites and can be found in the interior of their host organism.Monogenea are also parasitic worms. They are ectoparasites and can be found on the exterior of their host organism like on the gills of fish. Monogenes have an opisthaptor, located at the posterior end of their bodies, that can exhibit hooks, suckers, clamps, or some combination that allows them to attach to their host organism.Cestoda are parasitic tapeworms with repeating body segments called proglottids. They generally require at least two hosts to complete its life cycle, they lack a digestive system, and have a scolex which allows for attachment to a host.

Describe and trace the following lifecycles; human liver fluke, shistosomiasis, and beef tapeworm.

The normal habitat of the adults is in the bile passageways of humans and other fish-eating mammals. The lifecycle of the human liver fluke (Clonorchis sinensis) begins when the eggs, each containing a complete miracidium, are shed into water with the feces, but they do not hatch until they are ingested by the snail Parafossarulus or related genera. Eggs, however, may live for some weeks in water. In a snail, a miracidium enters the tissues and transforms into a sporocyst, which produces one generation of rediae. A rediae is elongated, with an alimentary canal, a nervous system, an excretory system, and many germ cells in the process of development. Rediae pass into the liver of the snail, where the germ cells continue embryonation and give rise to tadpolelike cercariae. These two asexual stages in the intermediate host allow a single miracidium to produce as many as 250,000 infective cercarie. Cercariae escape into the water and swim until they encounter a fish of family Cyprinidae. They then bore under scales into the fish's muscles. Here, cercariae lose their tails and encyst as metacercariae. If a mammal eats raw or undercooked infected fish, the metacercarial cyst dissolves in the intestine, and young flukes apparently migrate up the bile duct, where they become adults. There, the flukes may live for 15 to 30 years.The life cycle of schistosoma, blood flukes, is similar in all species. First, eggs are discharged in human feces or urine; if they get into water, they hatch as ciliated miracidia, which must contact the required kind of snail within a few hours to survive. In the snail, they transform into sporocysts, which produce another generation of sporocysts. Daughter sporocysts give rise to cercariae directly, without formation of rediae. Cercariae escape from the snail and swim until they contact bare human skin. They penetrate the skin, shedding their tails in the process, and reach a blood vessel where they enter the circulatory system. There is no metacercarial stage. The young schistosomes make their way to the hepatic portal system of blood vessels and undergo a period of development in the liver before migrating to their characteristic sites. As eggs are released by adult females, they are somehow extruded through the wall of veins and through the gut or bladder lining, to be voided with feces or urine, according to species. Many eggs do not make this difficult transit and are swept by blood flow back to the liver or other areas, where they become centers of inflammation and tissue reaction.The life cycle of beef tapeworms begins when shelled larvae (oncospheres) swallowed by cattle hatch and use their hooks to burrow through the intestinal wall into blood or lymph vessels and finally reach voluntary muscles, where they encyst to become bladder worms (juveniles called cysticerci). There, the juveniles develop an invaginated scolex but remain quiescent. When raw or undercooked "measly" meat is eaten by a suitable host, the cyst wall dissolves, the scolex evaginates and attaches to the intestinal mucosa, and new proglottids begin to develop. It takes 2 to 3 weeks for a mature worm to form. When a person is infected with one of these tapeworms, numerous gravid proglottids are expelled daily, sometimes even crawling out the anus. Humans become infected by eating rare beef, steaks, and barbecues.

What are the characteristics of the phylum Mollusca that distinguish it from other phyla?

The phylum Mollusca is the largest lophotrochozoan phylum and one of the largest and most diverse of all phyla. Its members range in size from very small organisms to the largest of invertebrates. Most diversity among molluscs is related to their adaptation to different habitats and modes of life, along with having a wide variety of feeding methods - ranging from sedentary filter feeders to active predators. There are many adaptations for food gathering in the phylum Mollusca, and there is an enormous variety in radular structure and function, particularly among gastropods. The evolutionary adaptations of certain features has led the phylum Mollusca to be set apart from every other phyla. Besides secreting the shell and forming the mantle cavity, the glandular mantle has variously modified into gills, lungs, siphons, and apertures, and it sometimes functions in locomotion, in the feeding processes, or in a sensory capacity. The shell, too, has undergone a variety of evolutionary adaptations, thus making molluscs one of the most successful groups in existence today.

Describe several features of the phylum Rotifera. What is a mastax with jaw-like trophy and a ciliated corona? Compare and contrast features of the phylum Gastrotricha. Describe and trace the following lifecycles; mictic and amictic cycles of rotifers.

The phylum Rotifera derive their name from the characteristic crown, or corona, that, when beating, often gives the impression of rotating wheels. Rotifers are common inhabitants of freshwater lakes and ponds. Some rotifers are epizoic (live on the body of another animal) or parasitic. Rotifers are very tolerant of environmental extremes. A rotifer's body comprises a head bearing a ciliated corona, a trunk, and a posterior tail, or foot. Except for the corona, the body is nonciliated and covered with a cuticle. Their ciliated corona, or crown, surrounds a nonciliated central area of their head, which may bear sensory bristles or papillae. Cilia on the corona beat in succession giving the appearance of a revolving wheel or pair of wheels. Their mouth is located in the corona on the midventral side. Coronal cilia function in both locomotion and feeding. The body wall of many species is superficially ringed, giving the appearance of segmentation. Although some rotifers have a true, secreted cuticle, all have a fibrous layer within their epidermis. The fibrous layer in some is quite thick and forms a caselike lorica, which is often arranged in plates or rings. Their foot is narrower and usually bears one to four toes. There are both sessile and creeping forms of rotifers. Rotifera have a syncytial epidermis and subepidermal muscles. Rotifers also have a complete digestive system. Their excretory system typically consists of a pair of protonephridial tubules, each with several flame cells that empty into a common bladder. They have a bilobed brain, and they have sensory organs that include paired eyespots, sensory bristles and papillae, and ciliated pits and dorsal antennae. Rotifers are dioecious.A mastax with jaw-like trophy and a ciliated corona is rotifers' pharynx (mastax) that is fitted with a muscular portion equipped with hard jaws (trophi), which is used for sucking in and grinding food particles. The mastax can be a crushing and grinding form among suspension feeders or a grasping and piercing form in predatory species. Some rotifers feed by sweeping minute organic particles or algae toward the mouth by beating the coronal cilia.The phylum Gastrotricha appear somewhat like rotifers superficially, but they lack a corona and mastax, and they have a characteristically bristly or scaly body. Gastrotrichs occur in fresh, brackish, and salt water. Their head is often lobed and ciliated, and the tail end may be greatly elongated or forked in some species. A partially syncytial epidermis is found beneath the cuticle. No specialized respiratory or circulatory structures occur in gastrotrichs. Their digestive system is complete and comprises a mouth, a muscular pharynx, a stomach-intestine, and an anus. Digestion appears to be extracellular. Protonephridia are equipped with solenocytes rather than flame cells. There is no body cavity in gastrotrichs, and the internal organs are all packed tightly into the compact body. Their nervous system includes a brain near the pharynx and a pair of lateral nerve trunks. Sensory structures are similar to those in rotifers, except that eyespots are generally lacking, although some species have pigmented eyespots (ocelli) in the brain. Sensory bristles, often concentrated on the head, are modified from cilia and are primarily tactile. Gastrotrichs are typically hermaphroditic, although the male system of some is so rudimentary that they are functionally parthenogenetic females. Like rotifers, some gastrotrichs produce thin-walled, rapidly developing eggs and thick-shelled, dormant eggs. Cleavage is not well studied but appears to be radial. Development is direct, and juveniles have the same form as adults.The mictic cycle of rotifers refers to the capacity of haploid eggs to be fertilized (that is "mixed") with the males' sperm nucleus to from a diploid embryo. The mictic cycle of rotifers refers to sexual reproduction taking place. Any one of several environmental factors - for example, crowding, diet, or photoperiod (according to species) - may induce amictic eggs to develop into diploid mictic females that produce thin-shelled haploid eggs. If these eggs are not fertilized, they develop into haploid males. But if fertilized, the eggs, called mictic eggs, develop a thick, resistant shell and become dormant. They survive over winter ("winter eggs") or until environmental conditions are again suitable, at which time they hatch into amictic females. Dormant eggs are often dispersed by winds or birds. The amictic cycle of rotifers refers to eggs that are diploid and develop parthenogenetically (without fertilization). The amictic cycle is "without mixing". Reproduction of some rotifers is parthenogenetic during the part of the year when environmental conditions are suitable. During most of the year, diploid females produce thin-shelled, diploid amictic eggs. Amictic eggs develop parthenogenetically into diploid (amictic) females. or The phylum Rotifera are bilateral symmetric marine organisms that can be parasitic or epizoic. A ciliated corona is a ciliated crown that when beat looks like a rotating wheel. The corona is a form of locomotion/feeding and may contain sensory bristles or papillae. A mastax is their pharynx that has fitted hard jaws, trophi, for sucking and grinding up food particles. Amictic eggs come from diploid females producing diploid amictic eggs. These diploid amictic eggs will develop into diploid females but environmental factors could lead them to turning into diploid mictic females. These mictic females will lay mictic eggs that can lead to males if they are unfertilized. Mictic eggs that are fertilized eggs that then develop a thick shell and become dormant. These eggs hatch when the environment is perfect and they hatch as females. Superficially, Gastrotricha seem similar to Rotifera but they lack a corona and mastax.

Sense organs in modern trematodes and cestodes are poorly developed. Likewise other features appear simpler than what is thought to be their ancestor stock (turbellarian flatworms). Typically we think of evolution as leading to increases in complexity, however, it often seems that in parasitic groups simplicity in morphology is selected over complexity. Discuss why this might be the case. Use the beef tapeworm as a model in your discussion. The beef tapeworm currently infests cattle, a mammal of more recent evolution. Did tapeworms only evolve as parasites after their modern hosts appeared? If not, what were they doing before then?

The simplicity of complex structures in parasites like the beef tapeworm could be caused by the fact that these systems are not useful to the organism. A complex system that houses many structures requires more energy and would overall be less efficient. It is also important to note that parasites do not have to 'hunt' for their own food in a traditional sense, instead they obtain nutrients from another organism. This allows the parasitic organism to focus on elements required for survival like feeding and reproduction. Beef tapeworms are a good example of this process because they have a simple body plan with suckers for attachment and modes for reproduction. These tapeworms were likely still parasitic before feeding upon cattle. It is possible that the tapeworm had a more generalized form that fed upon many different hosts and only recently began feeding on cattle due to its prevalence.

What is the function of the siphuncle in cephalopods?

The siphuncle in cephalopods is a cord of tissue running through the shell of a nautiloid that serves the function of connecting all the chambers within the animal's body. The siphuncle extends from the visceral mass.

Which is not true of Oligochaetes?

They have an open circulatory system.

Which is not a characteristic of leeches?

They have parapodia.

What functional problem results from torsion? How have gastropods evolved to avoid this problem?

Torsion leads to the rearrangement of the relative positions of the shell, the digestive tract and anus, the nerves that lie along both sides of the digestive tract, and the mantle cavity containing the gills. Before torsion occurs, the mouth is anterior and the anus is posterior. The asymmetrical foot retractor muscle running along the side of the gut and body organs contracts and pulls the shell and enclosed viscera (containing organs of the body) 90 degrees counterclockwise relative to the head. This movement brings the anus from the posterior to the right side of the body. The digestive tract moves both laterally and dorsally so that the anus lies above the head within the mantle cavity. After torsion, the anus and mantle cavity open above the mouth and head. The left gill, kidney, and heart atrium are now on the right side, whereas the original right gill, kidney, and heart atrium are now on the left, and the nerve cords form a figure eight. Because of the space available in the mantle cavity, the animal's sensitive head end can now be withdrawn into the protection of the shell. The functional problem that results from torsion is called fouling. Because of the body arrangement that results from torsion, where the anus opens over the head and gills, fouling can occur; fouling is where the wastes are washed back over the gills. Gastropods have evolved to avoid this problem because most living gastropods have lost the gill, atrium, and kidney of the right side, leading to a condition of bilateral asymmetry. Although loss of the right gill was probably an adaptation due to carrying a coiled shell, that condition, that is seen in most modern prosobranchs, made possible a way to avoid the fouling problem caused by torsion. Water is brought into the left side of the mantle cavity and out the right side, carrying with it wastes from the anus and nephridiopore, which lie near the right side. In prosobranchs with two gills, fouling is avoided by having the excurrent water go up and out through one or more holes in the shell above the mantle cavity. Opisthobranchs show partial or complete detorsion. Thus, the anus and gill (if present) are displaced to the right side or rear of the body. Opisthobranchs avoid the problem of fouling if the anus is moved away from the head toward the posterior. Pulmonates have evolved to avoid this problem because their anus and nephridiopore open near the pneumostome, and waste is expelled forcibly with air or water from the lung. or Torsion is a development stage in gastropods involving the rotation of the visceral mass, mantle, and shell with respect to the head and foot of the gastropod. This rotation effects the position of important systems and structures including the digestive tract, mantel cavity with the gills, anus, and nerves found along the digestive tract. This rotation brings the mantle cavity and the anus to an anterior position above the head. This can cause a problem known as fouling which occurs when the organism defecates onto its head and into the gills. However, gastropods have evolved ways to avoid this issue. For example, gastropods lacks their right gill, kidney, and right atrium. Another way to avoid this problem is by undergoing partial or complete detorsion and moving the anus posterior to the body.

Contrast asexual reproduction in triclad flatworms, trematodes, and cestodes.

Triclad flatworms reproduce asexually through fission. During this process, triclad flatworms will split into two halves and regrow the missing portion of each half. The outcome of this process is two fully functional triclad flatworms. In trematodes, asexual reproduction requires an intermediate host, usually a snail, in order to reproduce. The host organism is infected by the miracidium which becomes a sporocyst in the host's tissues. The sporocysts then make radiae and these radiae make more of themselves and also make cercaria. Asexual reproduction in cestodes is uncommon, but if it does occur it will happen through budding during the larval or metacestode stage.

Briefly describe the osmoregulatory system, the nervous system, and the sense organs of turbellarians, trematodes, and cestodes.

Turbellarians use a protonephridium, which involves a series of dead end tubules with flame cells at the ends, for osmoregulation. The protonephridium will elongate the cup of flame cells where beating flagella will drive fluid down the collecting ducts. In trematodes, only two protonephridial tubules form a median bladder that leads to the collecting ducts and then outside. In cestodes, there are 4 main protonephridia canals that run both the dorsal and ventral length of the body.The nervous system in turbellarians consists of a cluster of ganglion, which resemble a primitive brain, and sense organs like eye spots and chemoreceptors for finding food. The nervous system can be compared to nerve nets found in cnidarians. The trematode nervous system is less complex and involves two ganglia which are connected to longitudinal cords that stretch throughout the body. They have primitive sensory endings found around the oral sucker area and genital pores. The cestode nervous system resembles both turbellarian and trematodes. There is a ganglion present in the scolex. Similar to trematodes, cestodes have primitive sensory endings found around their oral sucker, holdfast, and genital pores.

The climate of southeastern U.S. and southeastern China are similar. Describe two separate factors that serve to keep flatworm parasites less common in the U.S. than in China.

Two factors serve to keep the flatworm parasites less common in the US than in China. The first factor is that the US does not consume as much raw meet as China meaning a decrease in potential infection through ingesting cysts. Cooking contaminated meat kills any potential parasites and will stop the possible transmission to a human host. The second factor is that there are more sanitation practices in the US compared to China. Expelling waste into the nearby water sources can contaminate the environment and spread disease. However, sanitation practices helps prevent feces, contaminated with parasitic eggs, from coming into contact with the intermediate hosts and then ingested and introduced into humans.

Cuticle

a needlike chitinous structure of the integument

nephridium

a protective noncellular organic layer secreted by the external epithelium

Setae

a wall between two cavities

dioecious

having male and female gonads in separate individuals

septum

segmentally arranged paired tubules specialized for excretion and osmoregulation

phototatic

unisexual reproduction