Chapter 33: An Introduction to Invertebrates

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Head of Planarian

Light-sensitive eyespots, lateral flaps to detect specific chemicals

Parapodia

Paddlelike appendages that assist aquatic annelids in locomotion. Each parapodium has numerous chaetae. In some species, they function as gills and may have many blood vessels.

Chelicerae

Pair of mouthparts in chelicerates that contain fangs and are used to stab and paralyze prey. Functions as pincers or fangs.

Trematodes

Parasites (such as blood flukes) have complex, alternating life cycles. Usually they have to infect a preliminary host where larvae grow before infecting the final host.

Trichinella spiralis

Parasitic nematode occurring in the intestines of pigs, rats, and humans, producing larvae that form cysts in skeletal muscles

Acanthocephala

Parasitic worms with a spiny proboscis for host attachment. Some can manipulate intermediate host behavior for transmission to final host.

Acoela

Refers to acoel flatworms that have a simple nervous system and a saclike gut. Not included in Platyhelminthes.

Ophiuroidea

Refers to brittle stars and basket stars, which have a distinct central disk and long, flexible arms. They move by lashing their arms in serpentine motions and lack the flattened disk found at the base of seastars.

Polyplacophora

Refers to chitons

Nematodes

Refers to roundworms like pinworms, Trichinella worms, and Ascaris worms. They have a fine tip at the posterior end and a blunt tip at the anterior end. They also have a tough cuticle that is shed periodically in accordance with growth. Though they do have an alimentary canal, they do not have a circulatory system. They are pseudocoelomates, free-living, and are known for their parasitism.

Crinoidea

Refers to sea lilies and feather stars. They use their long, flexible arms for suspension feeding and these arms encircle the mouth that faces upward away from the substrate.

Annelida

Refers to segmented worms that are coelomates. Divided into Polychaeta, Oligochaeta, and Hirudinea.

Pseudocoelomates with alimentary canal (digestive tube with mouth and anus); jaws (trophi); head with ciliated crown

Rotifera (rotifers)

Sixth mass extinction

Scientists have predicted/identified a new mass extinction is underway and an estimated 2-25 percent of species will go extinct; it is caused by humans

What groups are included in Medusozoa?

Scyphozoans, cubozoans, and hydrozoans

Cnidocytes

Special stinging structures on cnidarians that look like small harpoons and aid in defense and prey capture.

Why are hosts often oblivious to leech incisions?

They secrete an anesthetic

Like gastropods, how do earthworms expel waste?

Through the metanephridia, which are excretory tubules

Hemiptera

True bugs that are hemimetabolous and include stink bugs, bed bugs, and assassin bugs. They have two pairs of wings (one membranous, the other leathery), piercing/sucking mouthparts, and undergo incomplete metamorphosis (ENA).

Diptera

True flies, mosquitoes, gnats, midges. Has one pair of wings, halteres for balance, mouthparts for sucking, piercing, or lapping, and compound eyes.

What Dipterans are known for carrying disease? Name two.

Tsetse flies may carry African Sleeping Sickness (Trypanosoma) and mosquitoes may carry Malaria (Plasmodium vivax)

Leeches

Sedentarians that typically inhabit freshwater (though can be found in other habitats). Some are predators of other invertebrates, while still others are parasitic and obtain blood from a host by temporarily attaching themselves.

Leeches and earthworms are types of

Sedentarians, a type of Annelid

Centipedes

Segmented bodies, 1 pair of legs per segment, predators with a pair of venomous claws

What are the two variations to cnidarian body plans?

Sessile polyp and more motile medusa

Ammonites

Shelled cephalopod animals that were the dominant invertebrate predators for millions of years ending with the mass extinctions at the end of the Cretaceous period.

Cone snails

Shoot harpoon-like radula (laden with toxin) at prey (special Gastropod adaptation)

Zygentoma

Silverfish that are small and wingless with a flattened body and reduced eyes.

Nematocysts

Small capsules that contain a toxin which is injected into the prey or predators of cnidarians

Lancelets

Small, blade-like chordates that live in marine sands

How do Cnidarians respond to stimuli?

They have a nerve net - conducts nerve impulse to and from all parts of their body. They have no circulatory, respiratory or excretory systems.

Siphon

Tubelike structure through which water enters and leaves a mollusc's body. Water enters a bivalve's mantle cavity through an incurrent siphon and exits through an excurrent siphon.

Describe the predation habits of cephalopods

Use tentacles to grasp prey, have beak-like jaws to bite and transmit venom into prey

Pharynx in planarians

Used to spill digestive juices on to prey so that small pieces of food can be transferred to the gastrovascular cavity for further digestion

Priapula

Worms with a large, rounded proboscis at the anterior end; named after the Greek god of fertility, Priapos (who had a large, well... you get the idea)

-Unique stinging structures (nematocysts) housed in specialized cells (cnidocytes) -diploblastic -radially symmetrical - gastrovascular cavity (digestive compartment with a single opening)

Cnidaria (jellies, hydras, sea anemones, corals)

Corals

Cnidaria, Anthozoa - often secretes a hard exoskeleton of calcium carbonate, reefs are being destroyed by pollution, overharvesting, global warming, and ocean acidification

Sea Anemones

Cnidarians; have tentacles and a nerve net; live as sessile polyps - type of Anthozoan

Name six orders of winged insects

Coleoptera, Diptera, Hymenoptera, Lepidoptera, Hemiptera, Orthoptera

Which of the six previous insects undergo complete metamorphosis?

Coleoptera, Diptera, Hymenoptera, and Lepidoptera

Choanocytes

Collar cells that line the body cavity and have flagella that circulate water in sponges - engulfs food particles by phagocytosis

What developmental patterns do brachiopods and ectoprocts both have?

Deuterostomes

Ectoprocta

Ectoprocts (bryozoans) live as sessile colonies and are covered by a tough exoskeleton.

The gastrodermis of cnidarians is derived from

Endoderm

In Porifera, the outer layer consisting of tightly packed epidermal cells

Epidermis

What two clades are Annelids divided into?

Errantia and Sedentaria

Bivalves

Molluscs that have two shells held together by hinges and strong adductor muscles. No distinct head and no radula, some have eyes and sensory tentacles along the outer edge of their mantle.

Rotifera

Multicellular with specialized organs enclosed in pseudocoelom, complete digestive tract (alimentary canal); filter-feeder.

Tube feet

Extensions of an echinoderm's water vascular system that stick out from the body and function in movement and obtaining food.

Describe the head of Gastropods

Eyes are at the tip of tentacles

Compound eyes

Eyes made of many individual light detectors, each with its own lens

Mantle cavities of bivalves have what functions?

Feeding and gas exchange

What are the six major types of Lophotrochozoans?

Flatworms, rotifers, ectoprocts, brachiopods, molluscs, and annelids

Spongin

Flexible material that make up the skeleton of some sponges.

Spongocoel

Found in sponges, it is the central cavity into which water is drawn to filter nutrients

Molluscs are the animal group with the most documented extinctions. What two groups are at the greatest risk?

Freshwater bivalves and terrestrial gastropods

Ventral nerve cords

From the ganglia, a pair of ventral nerve cords runs the length of the body.

Tracheal tubes

Gas exchange in insects is accomplished by a branched, chitin-based trancheal system that carries oxygen directly to cells. Opens to the outside of the body via spiracles, which open and close to control air flow and water loss.

Decapods

Group of crustaceans that includes crabs and lobsters. The cuticle is reinforced, forming a dorsal shield on the cephalothorax called the carapace. The cuticle is hardened by calcium carbonate.

What threats do freshwater and terrestrial molluscs face?

Habitat loss, pollution, competition or predation by non-native species introduced by humans

Trophi

Hard, jaw-like elements within the mastax of rotifers

Ampulla

In echinoderms, the muscular sac that contracts to force water into the tube foot, allowing it to extend

Gonads

Ovaries and testes

What are the three main subgroups of crustaceans?

Isopods, decapods, and copepods

What is the purpose of the gastrovascular cavity of Cnidarians in contraction?

It acts as a hydrostatic skeleton in which contractile cells of the epidermis and gastrodermis can work.

Scyphozoans

Jellies

Describe the gills of terrestrial snails

Lack typical gills that compare to aquatic snails. Lining of the mantle cavity functions as a lung to exchange respiratory gases with the air.

What is another name for brachiopods?

Lampshells

Bdelloid rotifers

Large and ancient group that appears to have been completely asexual (parthenogenic) for a long time

Describe the shell in cephalopods

Largely reduced and internal, only chambered nautiluses have the exoskeletal shells

Mastax

The muscular pharynx in rotifers

Mollusca

(Snails, clams, squids, octopuses) have a soft bodies that in many species are protected by a hard shell

Describe the process by which trematodes infect their final host.

1. Mature flukes live in the blood vessels of the human intestine. 2. A female fluke will fit into a groove on the male's body and sexual reproduction will occur in the human host. The fertilized eggs exit the host in feces. 3. The feces enter a water source where the eggs develop into ciliates larvae, which will infect snails, the intermediate host. 4. Asexual reproduction occurs within the snail and the new motile larva exits the intermediate host. 5. Larvae penetrates the skin and blood vessels of humans working in fields irrigated with water contaminated with fluke larvae.

Cephalopods

A member of a group of molluscs that include squids and octopi. Only molluscs that have a closed circulatory system. They have well-developed sense organs and a complex brain.

Echinoderms

A member of a group of slow moving or sessile marine animals characterized by a rough or spiny skin, a water vascular system, a hard calcareous endoskeleton, and a radial symmetry in adults (larvae have bilateral symmetry), with examples such as sea stars, sea urchins and sand dollars

Chaeta

A chitinous projection from the cuticle found in annelids. Polychaeta have far more projections per segment than do Oligochaeta.

What life stage do some molluscs have that marine annelids and some other lophotrochzoans also have?

A ciliated larval stage, called the trochophore

Closed circulatory system

A circulatory system in which the oxygen-carrying blood cells never leave the blood vessels. Hence, the blood is distinct from the fluid in the body cavity.

Closed circulatory system

A circulatory system in which the oxygen-carrying blood cells never leave the blood vessels. The blood remains separate from the fluid in the body cavity.

Hydrozoans

A class of Cnidaria where most of the organisms alternate between polyp and medusa except hydras, which are only polyp. They can reproduce both asexually and sexually.

Lophophore

A crown of ciliated tentacles that function in feeding

Mantle

A fold of tissue that drapes over the visceral mass and secretes a shell (usually). In many molluscs, the mantle extends beyond the visceral mass, producing a water-filled chamber.

Planarians

A free-living flatworm found in unpolluted ponds and streams that can be predators or scavengers. They move by using cilia on their ventral surface and gliding along the mucus they secrete. Some swim using an undulating motion.

Mesohyl

A gelatinous region between the two layers of cells of a sponge

Pearl mussels

A group of freshwater bivalves that can make natural pearls, among the world's most endangered animals.

Arthropods

A group of organisms that are coelomates and have jointed appendages, a segmented body, an exoskeleton, bilateral symmetry, and reproduce sexually; insects, arachnids, millipedes and cenitpedes, and crustaceans. Thought to have arisen from Lobopods from the Cambrian explosion, which had body segments that were not diversified. Changes to existing Hox genes are hypothesized to have led to body segment diversity in modern species.

Arthropods

A group of organisms that have jointed appendages, a segmented exoskeleton, bilateral symmetry, and reproduce sexually; insects, arachnids, millipedes and cenitpedes, and crustaceans

Osculum

A large opening on a sponge through which filtered water is expelled

Chelicerates

A lineage of arthropods that includes horseshoe crabs, scorpions, ticks, and spiders. They have chelicerae for feeding, have an anterior cephalothorax, a posterior abdomen, simple eyes, and lack antennae.

Arachnids

A member of a major arthropod group that includes spiders, scorpions, ticks, and mites. They all have six pairs of appendages including the chelicerae for feeding, pedipalps, and four pairs of walking legs.

Gastropods

A mollusc with a single shell or no shell. Refers to snails and slugs.

Foot

A muscular organ that is used for locomotion and takes a variety of forms depending on the animal (trait of molluscs)

Water vascular system

A network of hydraulic canals unique to echinoderms that branches into extensions called tube feet, which function in locomotion, feeding, and gas exchange

Sea daisies

A new species found in 1986, small disk shaped animals with no arms. Tube feet are around the edges. Only three species are known.

Tapeworms

A parasitic flatworm characterized by the absence of a digestive tract (no gastrovascular cavity or mouth, absorbs nutrients from the host's intestine)

Madreporite

A perforated plate by which the entry and exit of seawater into and out of the vascular system of an echinoderm is controlled.

Lorica

A pocket formed by six plates surrounding the abdomen from which the head, neck, and thorax of a Loriciferan can project

Ectoprocts

A sessile, colonial lophophorate; also called a bryozoan. They superficially resemble clumps of moss. Often, the colony is encased in a hard exoskeleton studded with pores fro, which lophophores extend.

Molluscs

A soft-bodied animal characterized by a muscular foot, mantle, mantle cavity, and radula; includes gastropods (snails and slugs), bivalves (clams, oysters, and scallops), and cephalopods (squids and octopuses). Many species secrete a hard protective shell made of calcium carbonate.

Radial canal

A structure in echinoderms that runs the length of the arm, is part of the water vascular system

Tunicates

A subphylum of Chordata that includes about 3000 species of filter-feeding marine animals, such as sea squirts and salps. They are sessile marine chordates that lack a backbone.

Millipedes

A terrestrial arthropod that has two pairs of short legs for each of its numerous body segments and that eats decaying plant matter.

Myriapods

A terrestrial arthropod with many body segments and one or two pairs of legs per segment. Millipedes and centipedes comprise the two classes of living myriapods. Have antennae and three pairs of appendages modified as mouthparts, including the mandibles.

Cuticle

A tough external coat that ecdysozoans excrete as they grow by ecdysis

Mantle cavity

A water-filled chamber that houses the gills, anus, and excretory pores of a mollusc.

Hemichordata

Acorn worms (enteropneusts) and pterobranchs. They have gill slits and a dorsal nerve chord, members of the deuterostome clade.

Cells that can transport phagocytized nutrients to other cells of the sponge body, produce materials for skeletal fibers (spicules), or differentiate into any sponge cell needed

Amoebocytes

Metanephridium

An excretory organ found in many invertebrates that typically consists of tubules connecting ciliated internal openings to external openings. Removes wastes from the hemolymph.

Malpighian tubules

An excretory organ that is unique to insects, empties into digestive tract and removes nitrogenous wastes from the hemolymph, also plays a role in osmoregulation.

Eurypterids

An extinct carnivorous cheliceriform also called a water scorpion.

Radula

An organ covered with teeth that molluscs use to scrape food into their mouths

Porifera

Animal phylum that includes sponges, which are sessile and lack true tissues. They are filter-feeders, meaning that they trap particles that pass through the internal channels of their bodies.

Placozoa

Animalia phylum with only one species: Trichoplax adhaerens. They are thought to be basal and they consist of a simple bilayer of a few thousand cells.

Flatworms (Phylum Platyhelminthes)

Animals in this group exhibit bilateral symmetry and moderate cephalization (a head). They include planaria (nonparasitic), as well as flukes and tapeworms (Both parasitic). They are triploblastic and aceolomates

Loricifera

Animals only 0.1-0.4 mm in length; can move its head, neck, and thorax out of its lorica (pocket formed by six plates surrounding the abdomen)

Invertebrates

Animals that lack a backbone

Coelomates with segmented body wall and internal organs (except unsegmented digestive tract)

Annelida (segmented worms)

Cibrostatin

Antibiotic produced by sponges which holds promise due to its ability to kill penicillin resistant strains of streptococcus and some cancer cells.

Crustaceans

Any of various predominantly aquatic arthropods of the class Crustacea, including lobsters, crabs, shrimps, and barnacles, characteristically having a segmented body, a chitinous exoskeleton, and paired, jointed limbs. Only Arthropods with two pairs of antennae. Have appendages on their abdomen.

Visceral mass

Area beneath the mantle of a mollusc that contains the internal organs

Coelomates with segmented body, jointed appendages, and exoskeleton made of protein and chitin

Arthropoda (spiders, centipedes, crustaceans, insects)

Describe the circulatory system of Arthropods

Arthropods have an open circulatory system in which hemolymph is propelled by a heart through short anterior and then into spaces called sinuses surrounding the tissue and organs. Hemolymph reenters the heart through pores that are usually equipped with valves.

Insects

Arthropods with three body sections, six legs, one pair of antenna, and usually one or two pairs of wings that emerge from the dorsal side of the thorax (extensions of the cuticle)

How do lophophores function?

As the cilia draw water toward the mouth, the tentacles trap suspended food particles

Parthenogenesis

Asexual reproduction in which females produce offspring from unfertilized eggs.

What are the five clades of Echinoderms?

Asteroidea, Ophiuroidea, Echinoidea, Crinoidea, and Holothuroidea

Sponges are near the root of the phylogenetic tree for animals, so they are called

Basal animals

Describe the circulatory system in cephalopods

Closed circulatory system, only mollusc group with this quality

Brachiopoda

Brachiopods (lamp shells) that are often confused with Mollusca. The difference lies in the fact that brachiopods have a unique stalk for anchorage to the substrate and a crown of cilia (lophophore).

Archaeognatha

Bristletails (wingless, monocondylic).

How is the shell of Gastropods produced?

By the glands of the mantle

Cnidae

Capsule-like organelles that are contained in cnidocytes that can explode outward

What are the two clades of flatworms?

Catenulida and Rhaditophora

Totipotent

Cells that are able to develop into any type of cell found in the body. Helpful to sponges which must be able to adjust to an ever-changing environment.

Amoebocytes

Cells that move using pseudopods and digest food particles from choanocytes as well as carry nutrients to other cells. They also manufacture tough skeletal fibers within the mesohyl and are totipotent.

Describe the nervous system of insects.

Cerebral ganglion where the two nerve cords meet at the head. The antennae, eyes, and other sense organs are concentrated on the head.

Catenulida

Chain worms that reproduce asexually by budding at their posterior end

What are the three major lineages of Arthropods?

Chelicerates, myriapods, and pancrustaceans

Flagellated cells that line the spongocoel and create a current that draws in water through the pores and out through the osculum

Choanocytes

What two types of cells does Porifera have?

Choanocytes and amoebocytes

Coelomates with notochord; dorsal, hollow nerve cord; pharyngeal slits; post-anal tail

Chordata (vertebrates, lancelets, tunicates)

Eumetazoa

Clade of animals with true tissues

Medusozoa

Clade of cnidarians that produces a medusa

Lophotrochozoa

Clade of protostomes that exhibit a trochophore larvae stage or a lophophore feeding structure. Most diverse clade in terms of body plan. Includes flatworms, rotifers, ectoprocts, brachiopods, molluscs, and annelids.

Sedentarians

Clade that contains leeches and earthworms. Usually less mobile than errantians

Chitons

Class Polyplacophora. Has an oval-shaped body and a shell composed of eight dorsal plates (body is unsegmented, however)

Earthworms

Class Sedentaria of Annelida that have an alimentary canal and are hermaphrodites that do also cross-fertilize. Sexual reproduction occurs when earthworms align themselves in opposite directions to exchange sperm and asexual reproduction may occur by fragmentation and then regeneration. They also have cerebral ganglia and a closed circulatory system.

Anthozoans

Class of Cnidaria that occurs only as polyps, including coral and sea anemones.

Cubozoans

Class of Cnidaria with a box-shaped medusa stage and complex eyes. Often equipped with toxic cnidocytes. "Box-jellies" - an example would be sea wasps, which have a poison that is more deadly than cobra venom

Holothuroidea

Class of echinoderms including the sea cucumbers that lack spines, have reduced exoskeletons, are elongated at their oral-aboral axis, and five rows of tube feet.

Asteroidea

Class of echinoderms that includes sea stars and sea daisies. They have arms radiating from a central disk; have tube feet under their arms that can attach to substrate, enable locomotion, and grasp prey; can begin digestion externally; and can regenerated lost limbs.

How does digestion occur in planarians?

Completed within the cells lining the gastrovascular cavity, which has many fine subbranches to maximize surface area. Undigested wastes are ejected through an opening at the tip of the pharynx.

Describe the life cycle of hydrozoan Obelia (Similar in most other Cnidarians)

Consists of two stages, one that is asexual and another that is sexual. 1. Budding, a form of asexual reproduction, produces a colony of interconnected polyps. 2. The polyps are specialized for different purposes. Some have tentacles for feeding, while others lack tentacles and produce medusae by budding. 3. Medusae swim off, grow, and then reproduce sexually by meiosis and fertilization. 4. The zygote then develops into a solid ciliates larva called a planula. The planula will eventually settle and develop into a new polyp. The process can then restart.

What conditions may promote sexual reproduction in rotifers?

Crowding that produces dormant embryos

What do Echinoderms and Chordates have in common?

Deuterostome mode of development, such as radial cleavage and formation of the anus from the blastopore

Gastrovascular cavity

Digestive chamber with a single opening, in which cnidarians, flatworms, and echinoderms digest food

Alimentary canal

Digestive tube that extends from the mouth to the anus

Cnidarians have two layers of cells (ectoderm and endoderm) so they must be

Diploblastic

Trochophore larva

Distinctive larval stage observed in some lophotrochozoan animals, including some annelids and molluscs.

Hermaphrodites

Each individual functions as both male and female in sexual reproduction by producing both sperm and eggs. Porifera reproduce by a sequential male releasing sperm, which then joins with the egg in another sponge that is functioning as a female. The flagellated larvae then swims to a suitable substrate for its sessile adult development.

Pedipalps

Each of the second pair of appendages attached to the cephalothorax of most arachnids. They are variously specialized as pincers in scorpions, sensory organs in spiders, and locomotory organs in horseshoe crabs. Function for sensing, feeding, defense, or reproduction.

Coelomates with bilaterally symmetrical larvae and five-part body organization as adults; unique water vascular system; endoskeleton

Echinodermata (sea stars, sea urchins)

What are the two groups in Deuterostomia?

Echinoderms and Chordates - grouped together based on DNA similarities

The epidermis of cnidarians is derived from

Ectoderm

Triploblastic

Has three germ layers: the ectoderm, endoderm, and mesoderm.

Schistosomiasis

Helminth infection acquired from contact with water containing infected snails. (Blood flukes)

What groups belong to Deuterostomia?

Hemichordata, Chordata, and Echinodermata

What two orders of insects undergo incomplete metamorphosis?

Hemiptera and Orthoptera

Halteres

Highly modified wings used for balance rather than flight. Usually are club- shaped structures; found on the metathorax of true flies (Diptera).

Cnidarians have a variety of sessile and motile forms including what three groups?

Hydras, corals, and jellies

Lophophore

In some lophotrochozoan animals, including brachiopods, a crown of ciliated tentacles that surround the mouth and function in feeding.

Where are the gonads located in molluscs?

In the visceral mass

Hymenoptera

Includes ants, bees, and wasps. Social insects with two pairs of membranous wings, a mobile head, and chewing/sucking mouthparts. Some females have posterior stinging organs and still others in this order build elaborate nests.

Lepidoptera

Includes butterflies and moths, which have a long feeding proboscis.

Ctenophora

Includes comb jellies, which are diploblastic and radially symmetric. They have eight "combs" of cilia that propel the animal through the water and make up much of the ocean's plankton. Contact with comb jellies often spurs specialized cells to break open and cover the prey in sticky threads.

Cnidaria

Includes corals, jellies, and hydras. They are diploblastic, radially symmetric, and have a gastrovascular cavity with a single opening that serves as the mouth and anus.

Lophophorates

Includes ectoprocts and brochiopods; all have a crown of cilia that helps in absorbing water and trapping suspended food particles (lophophores); have a U-shaped alimentary canal and no distinct head; have a true coelom and are sessile

Orthoptera

Includes grasshoppers, crickets, and katydids. Mostly herbivorous, have hind legs adapted for jumping, two pairs of wings (one leathery, one membranous), and biting/chewing mouthparts.

Echinoidea

Includes sea urchins and sand dollars, which have no arms, five rows of tube feet for slow movement, and muscles that pivot their long spines for locomotion and protection (urchins).

Hemimetabolous

Incomplete metamorphosis where the immature resemble the adults but some features are missing or different (wings, reproductive organs, color, shape, etc.).

What is the evolutionary advantage of lacking a body cavity and being relatively flat for flatworms?

Increases surface area to volume ratio. By placing all their cells close to water in the surrounding environment or their gut, gas exchange and the elimination of waste can occur by diffusion across the body surface.

Complete metamorphosis

Insect development consisting of four stages: egg, larva, pupa, and adult

Incomplete metamorphosis

Insect development consisting of three stages: egg, nymph, and adult (ENA). Nymphs resemble the adults but have different body proportions and lack wings. Each molting results in a nymph that looks increasingly like the adult. The final molt is where the insect reaches full size, acquires wings, and becomes sexually mature.

Pancrustaceans

Lobsters and other crustaceans, as well as insects and their relatives

Coelomates with lophophores (feeding structures bearing ciliated tentacles)

Lophophorates (Ectoprocta and Brachiopoda)

What are the three groups of Bilateria?

Lophotrochozoa, Ecdysozoa, and Deuterostomia

What groups belong to Ecdysozoa?

Loricifera, Onychophora, Nematoda, Tardigrada, and Arthropoda

Ganglia

Masses of nerve cell bodies at the anterior end of flatworms used for sensory input.

Coelomates with three main body parts (muscular foot, visceral mass, mantle); coelom reduced; most have a hard shell made of calcium carbonate

Mollusca (squids, snails, clams)

What are the two divergent clades of Cnidaria?

Medusozoans and Anthozoans

Bilateria

Members of the branch of eumetazoans possessing bilateral symmetry and have triploblastic development. Most have a digestive tract with two openings (a mouth and an anus) and a coelom

Bilateria

Members of the branch of eumetazoans possessing bilateral symmetry. Includes Lophotrochozoa, Ecdysozoa, and Deuterostomia

The bilayer of a sponge is separated by this gelatinous matrix

Mesohyl

Copepods

Minute shrimp-like crustaceans; often they are the most common zooplankton in estuarine waters. Some are grazers, while others are predators. A surprising example would be barnacles.

Errantians

Mobile, mostly marine organisms that have parapodia on each body segment

Planarian Nervous System

More complex and centralized than the nerve nets of cnidarians

Rhabditophora

More diverse and include both free-living and parasitic species of flatworms

Medusa

Motile stage of the life cycle of a cnidarian that has a bell-shaped body. Free-swimming and resembles a flattened, mouth-down version of the polyp.

Describe the sensory system of Arthropods

Much more complex, yet focused at the anterior end with eyes, olfactory receptors, and antennae

Cylindrical pseudocoelomates with tapered ends; no circulatory system; undergo ecdysis

Nematoda (roundworms)

Mollusc nervous system

Nerve ring around the esophagus, from which nerve cords extend

Protonephridia

Networks of tubules with ciliated structures called flame bulbs that pull fluid through branched ducts opening to the outside

Mandibles

One of a pair of jaw-like feeding appendages found in myriapods, hexapods, and crustaceans.

Isopods

One of the largest groups of crustaceans, primarily aquatic, but including pill bugs common under logs and moist vegetation next to the ground.

Proglottids

One of the segments of a tapeworm, sacs containing both male and female reproductive organs. After sexual reproduction, these sacs are released via the posterior end of the tapeworm and later in the feces of the host.

Mollusc hearts

Open circulatory system that has a dorsal heart that pumps hemolymph (circulatory fluid) through arteries into sinuses (body cavities), continuously bathing organs in hemolymph

What type of circulatory system do insects have?

Open circulatory system where the heart drives the hemolymph through the system.

Spiracles

Openings in the exoskeleton of arthropods, such as the grasshopper, that connect to internal cavities called hemocoels where respiratory gases are exchanged

Coleoptera

Order of beetles that have two pairs of wings (one is stiff, the other is membranous), an armored exoskeleton, and mouthparts for biting and chewing

Filter feeders

Organism that takes in water to filter out the food and then releases the extra water (clam, oysters, sponge)

Book lungs

Organs of gas exchange in spiders, consisting of stacked plates contained in an internal chamber.

Why can't Polychaeta, Oligochaeta, and Hirudinea (leeches) be characterized as such?

Phylogenomic studies have indicated that oligochaetes are a subgroup of polychaetes and that leeches are a subgroup of oligochaetes

Platyhelminthes

Phylum of flatworms, including tapeworms, planarians, and flukes. They have bilateral symmetry and a central nervous system that processes information from sensory structures. They have no body cavity (acoelomates) or specialized organs for circulation.

Onychophora

Phylum of velvet worms that originated in the Cambrian explosion. They formerly inhabited the ocean, but now they are found only in humid forests. They have fleshy antennae and several dozen pairs of saclike legs.

Tardigrada

Phylum of water bears that can survive dormant in conditions less than -200 degrees Celsius. They have a rounded shape, stubby appendages, and a lumbering, bearlike gait.

How do planarians reproduce?

Planarians are hermaphrodites and can reproduce sexually, or asexually through fission

Dorsoventrally flattened acoelomates; gastrovascular cavity or no digestive tract

Platyhelminthes (flatworms)

What groups belong to Lophotrochozoa?

Platyhelminthes, Ectoprocta, Rotifera, Brachiopoda, Acanthocephala, Nemertea, Cycliophora, Annelida, and Mollusca

What are the four major clades of Molluscs?

Polyplacophora (chitons), Gastropoda (snails and slugs), Bivalvia (clams, oysters, and other bivalves), and Cephalopoda (squids, octopuses, cuttlefishes, and chambered nautiluses)

Areas on a sponge through which water enters that are formed by doughnut-shaped cells that span the body wall

Pores

Informally called "sponges"

Porifera

Lack true tissues; have choanocytes (flagellated collar cells for ingesting food)

Porifera (sponges)

Podium

Portion of the tube foot that expands and contacts substrate when the ampulla forces water in. Attachment to substrate occurs when the podium secretes adhesive chemicals and detach with de-adhesive chemicals and forcing water back into the ampulla to make the tube foot contract.

Free-living Rhabditophorans

Predators and scavengers in a wide range of aquatic habitats that are well-known for containing species of the genus Dugesia, or planarians.

Nemertea

Proboscis worms or ribbon worms; lack a true coelom but they have an alimentary canal and a closed circulatory system

Molting

Process in which an arthropod sheds its exoskeleton and manufactures a larger one to take its place. Also known as ecdysis.

What is the purpose of the shell of Gastropods?

Protecting the animal's soft body from injury and dehydration, protecting against predation

Echinodermata

Radially symmetrical marine invertebrates including e.g. starfish and sea urchins and sea cucumbers. They are deuterostomes and are bilaterally symmetrical as larvae but not adults. They use internal canals that pump water for locomotion and feeding.

Water passing through pores enter this cavity

Spongocoel

Brachiopods

Superficially resemble clams and other hinge-shelled molluscs, but the two halves of the shell are dorsal and ventral rather than lateral as in clams. All are marine and attach themselves to substrata by use of a stalk.

Ecdysozoa

Supergroup of protostomes; characterized by periodic molting of their exoskeleton. Includes the roundworms (nematodes) and arthropods.

What type of feeder are bivalves?

Suspension or filter feeders

Scolex

The anterior end (head) of a tapeworm, bearing suckers and hooks for attachment to the intestinal lining of the host.

Hirudin

The anticoagulant secreted by leeches into the wound they create to prevent clotting

Central disk

The central portion of a starfish. The arms of a starfish radiate from the central disk as well as a nerve ring and nerve cords.

What covers the body of an arthropod? What is this structure made of?

The cuticle, which is made of layers of protein and the polysaccharide chitin

Describe locomotion in cephalopods

The foot has been modified into an excurrent siphon. Squids dart around by drawing water into their mantle cavity and ejecting it through the excurrent siphon. They steer by pointing the siphon in different directions.

Mesoglea

The jellylike substance that separates the epithelial cells in a cnidarian

Proboscis

The long snout of an animal; a nose, especially a prominent one; a tubular organ

Cycliophora

The most recently named phylum; its only known member is Symbion pandora, a tiny invertebrate first identified in 1995 when a Danish biologist found specimens on the mouthparts of a Norwegian lobster. It is believed to be closely related to the marine phyla Entoprocta and Ectoprocta (Bryozoa), which are not discussed here. They have a bizarre life cycle in which males impregnate females while they are still developing in their mother's bodies. The females then escape to another part of the lobster and release the offspring, which will find a new lobster to restart this process.

Nematoda

The phylum of roundworms found in aquatic habitats, wet soil, moist tissues of plants, and body fluids of animals. They are parasitic and have a tough cuticle that coats their bodies.

Chordata

The phylum of the animal kingdom that includes vertebrates and two basal groups of invertebrates (lancelets and tunicates). They are bilaterally symmetrical, coelomates, and have segmented bodies.

Chordata

The phylum of the animal kingdom that includes vertebrates. The three groups of invertebrates in this phylum, however, are lancelets, tunicates, and hagfishes.

Annelida

The phylum to which segmented worms belong.

Hemocoel

The primary body cavity of most invertebrates, containing circulatory fluid. Name for the hemolymph-filled body sinuses.

Polyp

The sessile, tubular form of a cnidarian with a mouth and tentacles at one end and a basal disk at the other. The aboral (end opposite the mouth) end adheres to the substrate and they extend tentacles, waiting for prey. Examples include hydras and sea anemones.

Describe the body plan of molluscs.

They are coelomates and they have a foot, a visceral mass, and a mantle.

Rotifers

Tiny animals that inhabit fresh water, the ocean, and damp soil. They do not have a gastrovascular cavity and they instead have an alimentary canal. They are pseudocoelomates and they have a crown of cilia for drawing water into the mouth. Trophi at the back of the mouth enable rotifers to grind up food.

Parasitic Rhabditophorans

Trematodes and tapeworms, which live in or on other animals. Many have suckers or tough coverings.


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