Unit 4 - Animals

lophophore

circulae or U-shaped ring of hollow, ciliated tentacles around the mouth; used for food collection and gas exchange; evolved independently at least twice; all animals with a lophophore are *sessile* as adults.

What are the basic body features of mollusks?

mollusks are the most diverse group of lophotrochozoans and have the same three components: a foot, a visceral mass, and a mantle.

Distinguish a brachiopod from a mollusk bivalve

the brachiopod is split ventral and dorsal instead of lateral like the mollusk and they evolved their shell independently.

protostome

"mouth first"; the blastopore of the embryo becomes the mouth and the anus forms later on in development

deuterostome

"mouth second"; the blastopore of the embryo becomes the anus and the mouth forms later on in development

Main features, lifestyle, and 'basic body plan' in bivalves

*bivalves*: includes clams, oysters, scallops, and mussels in both freshwater and marine environments with ~30k known species. they have a hinged, 2-part shell that extends over the sides of the body as well as into mud & sand. they feed by taking in water w/ large gills (main site of gas exchange). water and gametes exit through the excurrent siphon and fertilization takes place in open water in most species.

Main features, lifestyle, and 'basic body plan' in cephalopods.

*cephalopods*: includes squids, cuttlefish, octopuses, and nautiluses. ~800 living species. they have a head w/ complex sensory organs and the head is closely associated w/ a large branched foot that bears the arms and/or tentacles and a siphon and use the arms to capture and subdue prey.

Main features, lifestyle, and 'basic body plan' in chitons

*chitons*: 8 overlapping calcareous plates w/ a girdle that protects the internal organs & muscular foot. bilaterally symmetrical with internal organs and digestive and nervous systems. mainly marine omnivores. moves slowly by means of rippling waves of muscular contraction.

Main features, lifestyle, and 'basic body plan' in gastropods

*gastropods*: most species rich and widely distributed mollusks w ~85k living species. moves with either a muscular foot or a swimming organ. includes snails, whelks, limpets, slugs, and nudibranchs.

We discussed 2 sister groups of arthropods: tardigrades (moss piglets) and onychophorans (velvet worms). Give characteristics of each. On what basis are they considered sister groups of arthropods?

*tardigrades* have fleshy, unjointed legs and use their fluid-filled body cavities as hydrostatic skeletons. they are tiny (0.5-1.5mm long) and lack a circulatory system and gas exchange organs. *onychophorans* are soft, fleshy, unjointed, claw bearers with elongated bodies. they have soft segmented bodies covered by a thin cuticle of chitin and similar to tardigrades use their body cavity as a hydrostatic skeleton.

What is 'cleavage' with respect to embryonic development?

A *cleavage* is the early cell divisions of an embryo.

What are the synapomorphies of the protostomes?

1. An anterior brain that surrounds the entrance to the digestive tract 2. A ventral nervous system consisting of paired or fused longitudinal nerve cords

Name the five major groups of animals.

1. filter feeders: aka *suspension feeders*, strain small animals from their environment 2. herbivores: eat plants or parts of plants 3. predators: capture and eat other animals 4. parasites: live in or on other organisms to obtain energy and nutrients 5. detritivores: feed on dead animals

Describe a bryozoan colony, and explain how some individual animals can show differentiation of roles/physiology in the colony.

A colony consists of 1-2mm (small) individuals connected by strands of tissues where nutrients are moved. The colonies can have >2million individuals stemming from asexual reproduction. In some colonies, individuals are specialized for feeding, reproduction, defense, or support. Colonial species are sessile.

Appendages

A projecting part of an invertebrate or other living organism, with a distinct appearance or function.

Why is the body of a sponge thought to be most similar in morphology to the ancestral form (compare to choanoflagellate colony)? What characteristics do sponges have that are typical of all animals? How do most sponges acquire nutrients?

A sponge moves food by beating the flagella of its *choanocytes* which have similar morphology to *choanoflagellates*. The function and shape of the two cells show a link between sponges in animal clade and choanoflagellates in protists. Sponges have the animal feature of multicelluterm-3larity and specialization of these clusters.

Describe the key features of the arthropod cuticle, and the consequences (advantages & disadvantages) for organisms that have this feature.

Advantages of exoskeleton: they allow complex movements due to jointed appendages, they provide protection against physical damage and abrasion, and they increase leverage Disadvantages of exoskeleton: they cannot stretch or expand, special modification are required for gaseous exchange and sensory pick up, it is a major restriction on growth, and it needs to be shed at regular intervals.

triploblastic

An embryo with three germ cell layers: endoderm, ectoderm, and mesoderm. This is a synapomorphy.

Symmetry vs Asymmetry

Animals that can be divided along at least one plane into similar halves is *symmetrical* while animals with no planes of symmetry are *asymmetrical*.

Describe the arrow worms. What are the features of this group that place them as a sister clade to the rest of the protostomes? What features of this group suggest that deuterostome development is the ancestral condition?

Arrow worms are marine hermaphroditic invertebrates with a three-part body organization (head, trunk, tail) and fins for grasping spines for a predatory lifestyle. Arrow worms are special since their blastopore becomes an anus (like a deuterosome), but they have ventral nerve cords and a spiral cleavage. This places them as the sister clade to the rest of the protosomes and suggest that a deuterostome is an ancestral condition.

What adaptation(s) may have allowed the Bdelloid rotifers to evade the accumulation of deleterious mutations while using only asexual reproduction?

Bdelloid rotifers have on female eggs which can develop without fertilization, but usually results in deleterious mutations however it's suspected they pick up fragments of genes from their environment during desiccation-rehydration cycles.

Why is C. elegans a useful model organism?

C.elegans is easy to cultivate, matures n 3 days, and has a fixed number of body cells. it's entire genome has been sequenced so it's an ideal organism for research.

mesoderm

Center layer of the embryo; gives rise to the skeleton, circulatory system, muscles, excretory system, and most reproductive system and most organs.

What does it mean to be a colonial organism?

Colonial organisms are clonal colonies composed of many physically connected, interdependent individuals. The subunits of colonial organisms can be unicellular, as in the alga Volvox (a coenobium), or multicellular, as in the phylum Bryozoan.

Describe the Ctenophores. What are the highly-derived features of this group?

Ctenophores have radial symmetry and a diploblastic body plan with a gelatinous extracellular matrix between them called the *mesoglea*; they also have a *complete gut* (contrast to sponges). The synapomorphies of ctenophores are: 8 comb rows of fused cilia, pair of tentacles, colloblast cells on tentacles, bi-radial symmetry with oral-aboral axis, a well- developed mesenchyme, & third class of hox genes

Gastrulation

Development of a blastula into a gastrula with a hollow cusp and three layers of cells

What is the photosynthetic endosymbiont of (some) corals, and how is it related to the coral bleaching?

Dinoflagellates (zooxanthellae) are photosynthetic and have a symbiotic relationship with corals which keeps them strong. In coral bleaching, corals dispel dinoflagellates and become vulnerable to the dangerous environments such as ocean acidification (rising CO2), N2 human run-off, and warming.

Do the insects that have direct flight muscles comprise a clade?

Direct flight insects do *not* comprise a clade.

Pterygote insects have two pairs of wings. Compare/contrast direct and indirect flight muscles. Which is the ancestral condition?

Direct flight means the muscles are "directly" attached to the wings (wings to the exoskeleton) and move similar to a rowboat. This is the ancestral condition. Indirect flies mean the muscles deform the wall of the thorax or move by pushing on the body wall. This is a derived trait.

Compare & contrast free-living flatworms vs parasitic flatworms.

Flatworms in general have no circulatory system, are hermaphorditic, and can regenerate missing body pieces with mitosis. Free living flatworms have basic nervous systems that senses food, chemicals, and movement. Parasitic flatworms have hooks on the mouth to secure attachment to the host.

Describe the reproduction strategy of free-living flatworms

Free-living flatworms are hermaphroditic and they typically reproduce both sexually and asexually. The majority of sexual reproduction is through cross-fertilization (where both individuals fertilize each other). After mating, both flatworms can lay fertilized eggs. If no other flatworms are present, they can also reproduce asexually by fertilizing their own eggs. Fertilization happens internally. Then the flatworms release the fertilized eggs, or zygotes, into the water, where they hatch.

Anterior, posterior, ventral, & dorsal

Front - *anterior*, back - *posterior*, stomach/underside - *ventral*, back/surface - *dorsal*

What are hox genes? Hox genes are not a synapomorphy of all animals (we discussed at length one group that is missing these genes entirely),but are present in most animals. How does the arrangement of hox genes on the chromosome(s) correspond to where these genes are expressed in the embryo?

Hox genes are a group of related genes that control the body plan of an embryo along the craniocaudal axis. The head-tail organization of most animal bodies is under the control of different hox genes. Hox genes align from head to tail in the 5' to 3' direction.

Central Nervous System (CNS) vs Nerve Nets

In bilaterians, the CNS coordinates muscle movement which allows movement of body parts and appendages; the CNS processes sensory information. The nerve net in invertebrates consists of interconnected neurons that diffuse network which conducts impulses in all directions from a point of stimulus and is lacking a brain or any form of cephalization.

endoderm

Innermost germ layer of the embryo; gives rise to the digestive and respiratory tracts and any structures associated with them.

Know the 3 body regions of insects. Which region lack appendages?

Insects have a head, abdomen, and thorax. The abdomen lacks appendages.

ectoderm

Outermost germ layer of the embryo; gives rise to skin, sense organs, and the nervous system

Placazoans are often called the simplest free-living animals. What two features support this statement? Why are these organisms not considered a sister clade to the rest of the animals?

Placazoans have the smallest amount of DNA measured for an animal and only have four types of cells that make up their body and lack true organs no gut, mouth, or nervous system. They are not a sister clade for their simplicity because it's hypothesized that their simplicity is secondarily derived.

Describe the ribbon worms, especially the unusual proboscis.

Ribbon worms have simple nervous and excretory systems and have a closed circulatory system and a complete digestive system. Small ribbon worms move by slowly beating their cilia, but larger ones employ waves of muscle contractions . They also have a fluid filled body cavity called the *rhynchocoel* within the hollow, muscular *proboscis* which is the feeding organ that extends the length of the body. The proboscis also has sharp stylets which can pierce prey and discharge paralysis toxins.

Can sponges distinguish between self and non-self?

Sponges can recognize themselves and have self recognition. An example of this is the *blender sponge experiment* where two different types of sponges were put in a blender then meshed together. The study concluded sponges have self recognition because the sponges separated and connected to their respective bodies again.

What kind of immune system does a sponge have?

Sponges have an innate immunity which means it is not very complex. They simply reject any graft that is not recognized as a member of their own species, but they can recognize their own kind and accept grafts them.

Cephalization

Strongly coordinated with bilateral symmetry; concentration of sensory organs and nervous tissue at the anterior end

Describe the typical features of an animal. Few of these are completely diagnostic, and yet the data does support the notion that this is a monophyletic group. The synapomorphies of animals are features critical for multicellularity. Name them.

The animal clade is all multicellular (unlike bacteria, archaea, and protists), has a heterotrophic metabolism, internal digestion in the gut, and a unique muscle-nervous system, but these are not diagnostic. Diagnostic features are: a. a common set of extracellular matrix molecules (collagen & proteoglycans) and b. unique junctions between cells (tight & gap junctions, desosomes).

How is a new 'founder' produced? Recall that asexual reproduction of the founder results in a new colony.

The colonies are found from the ancestrula or the founding zooid that undergoes asexual budding to form a bryozoan colony. Eggs are fertilized and brooded internally then larvae are released to find a new attachment site. When the founder attaches to the surface, a colony forms by budding.

Chelicerates: have a two part body, chelicerae and include 3 that we discussed at length: horseshoe crabs, sea spiders (Pycnogonids), and arachnids. Arachnids are the terrestrial clade - what common groups are included? What does it mean that they have a "simple lifecycle"? Most are predators and parasites. What structure do spiders use to inject their venom, if present?

The common groups of arachnids are spiders, scorpians, harvestmen (daddy-long-legs), mites, and ticks. Their simple lifecycle means that the offspring are born as mini adults and begin an indepdendet life and simply grow bigger. They usually use fangs/chelicerae to inject venom into prey. They have cephalothorax and abdomen.

Ctenophore-First Phylogenetic Theory

The ctenophore-first theory implies that the gut was independently evolved with extracellular disgestion or a loss of of the gut, implying parallel evolution of the gut or the loss of it in sponges.

A key feature of the ecdysozoans is the cuticle. Why must it be molted? How many times has this trait appeared in evolutionary history?

The cuticle allows the animal to grow and protects and supports the animal, but it must be shed for the animal to continue to grow. the molting process has only evolved once which ties together the clade.

segmentation

The division of the body into segments; facilitates specialization of different body regions and allows the animal to alter the shape of its body

Name the three extant arthropod clades

The extant groups are the Chelicerates (arachnids && relatives), Myriapods (millipedes & centipedes), and Pancrustacea ("Crustaceans": shrimps, barnacles, crabs, and Hexapods: insects and wingless relatives)

body plan

The general structure of an animal, the arrangement of its organ systems, and the integrated functioning of its parts.

What is the function of the lophophore in brachiopods & phoronids?

The lophophore is a ring of tentacles that surround the mouth. In brachiopods and phoronids, the beating cilia of the lophophore draws water into the shell and traps food to be transferred to the mouth.

How do comparisons of the bryozoans/entroproct clade and the flatworm/rotifer/gastrotrich clade show that body cavity structure similarities can be the result of convergent evolution?

The lophotrochozoan clade has groups with acoelomate subgroups (flatworms) and pseudocoelomate subgroups (rotifers & gastrotrichs), but the bryozoans are coelomate and the entoproct are acoelomate and are the closest relatives.

Describe the basic sponge body plan.

The most basic body plan is called *asconoid*. In asconoid sponges the two major cell layers surround a fluid-filled cavity called the *spongocoel*, the large central cavity of sponges . Water is pumped directly through pores, called *ostia*, into the spongocoel and then out of the sponge through an opening called the osculum (plural oscula). The spongocoel is lined with specialized digestive cells called choanocytes that filter and take in food.

What is the gastrovascular cavity? What does it mean to lack a complete digestive tract?

The mouth of a cnidarian is connected to a blind sac and this is the cavity. It functions in digestion, circulation, and gas exchange. This is an *incomplete digestive tract* because the opening is both he mouth and anus versus a complete tract which has two openings.

Mandibulates: includes the two other extant arthropod groups myriapoda & pancrustaceae, which share two features: mandibles & sensory antennae. Name/distinguish between the two general groups included in the myriapoda. What environments are they found in and which are predators?

The myriapods include millipedes and centipedes and are a terrestrial clade. Centipedes have one pair of legs per segment whereas millipedes have two pairs of legs per segment. Centipedes prey on small animals and insects while millipedes usually scavenge and eat plants.

blastopore

The opening created by the invagination of the vegetal pole during gastrulation of animal embryos; in some cases this opening becomes the anus; mouth-like opening of the archenteron on the surface of an embryo in the gastrula stage.

Which is the more diverse group (both in number of species & number of individuals): proto- or deuterostomes?

The protosomes are more diverse than deuterostomes.

Sponge-First Phylogenetic Theory

The sponge-first theory is the *traditional theory* that the sponges or porifera are the basal group lineage with eumetazoans because of their feeding choanocytes being similar to choanoflagellates indicating a primitive trait. With choanocytes being the primitive digestion and feeding trait, the evolution of the *gut* indicates the choanocytes were replaced and remade to better benefit the more recent animals.

What are the earliest known arthropod group with jointed appendages, and when were they abundant?

The trilobites were the earliest known arthropod group and they were most abundant during the Cambrian and Ordovian period, but went extinct during the great Permian extinction.

Name the two major clades of protostomes. What is/are the key synapomorphies of lophotrochozoans and ecydsozoans?

The two clades of protostomes are the lophotrochozoans (ciliated feeding structures) and ecydsozoans (chitinized *cuticle molting* process)

What are the two phases of a typical Cnidarian lifecycle? Which is the sexual phase? Is this alternation of generations?

There is the sessile polyp stage and motile medusa stage. The polyp stage creates a cylinder stalk which attaches to the substrate and asexually creates a medusa. The medusa is free-swimming and reproduce sexually with eggs and sperm by meiosis and releasing the gametes into the water. This is *not* alternation of generations.

Describe the Cnidarians.

They are the largest and most diverse group of non-bilaterian animals containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is *cnidocytes*, specialized cells that they use mainly for capturing prey

Radial vs. Bilaterial

When an organism has *radial symmetry* the body parts are arranged around one main axis at the center of the body (ex. comb jellies, sea anemones, jellyfish) while *bilaterial symmetry* means the organism has a distinct front and back but can be split into mirror images left and right through the midline of the body

What is a hydrostatic skeleton? Describe how a snail might use such a system for movement. Which condition allows for a hydrostatic skeleton: acoelomate, pseudocoelomate, coelomate?

a hydrostatic skeleton is a flexible skeleton supported by fluid pressure. the skeleton allows free movement for soft bodied animals and is only possible with a coelomate for the organs to be placed.

Body cavity (acoelomate, pseudocoelomate, coelomate)

acoelomate: animal that lacks a body cavity and instead has a mass of cells called the *mesenchyme* pseudocoelomate: animal has a body cavity, however it is not formed from the mesoderm and organs are suspended in the *pseudocoel* coelomate: body cavity is present and formed from the mesoderm lined with *peritoneum* tissue that also surrounds the organs

What are the key features of annelids? Why are they restricted to aquatic or moist habitats?

annelids are segmented and lack a rigid external protective covering and instead have a thin, permeable body wall for gas exchange. this is why they are restricted to moist habitats because they lose body water rapidly in dry air.

How do cephalopods accomplish jet propulsion? Flight?

cephalopods have excurrent siphons modified to allow the animal control over the volume of water in the mantle cavity and can bring in and expel water. this modification allows the forceful push of water.

Which is the ancestral condition, triploblastic or diploblastic development?

diploblastic embryo is ancestral while triploblastic is a synapomorphy.

diploblastic

embryo with two germ cell layers: ectoderm and endoderm

Which group contains the only terrestrial mollusks, and how have they adapted to breathe air?

gastropods are the only group with terrestrial mollusks because land snails breathe air and their mantle tissue is modified into a highly vascularized lung.

Why are octopuses able to pass through small openings?

most cephalopods have external chambered shells, but octopuses have lost this shell so they can compress their bodies.

What are some roles of nematodes in soil ecosystems? As predators/parasites?

nematodes are usually scavengers in the upper layers of the soil, on the bottoms of lakes and streams, and in marine sediments. many nematodes are predator and feed on protists and small animals they also parasitize humans and cause serious diseases like trichinosis and elephantiasis.

What adaptations allow pogonophores to obtain nutrition?

pogonophores can directly absorb dissolved organ matter from the water, but most nutrients come from endosymbiotic bacteria in the specialized trophosome organ. The bacteria oxidize hydrogen sulfide and other sulfur compounds and fix carbon form methane in the process. This is facilitated by the trophosome's hemoglobin which give it a red color.

ecdysis

process where ecdysozoans shed their protective external cuticle which as an exoskeleton made of chitin. this process and feature only evolved once.

trochophore

some lophotrochozoans in the larval form use cilia for locomotion and move by beating a band of cilia; cilia movement brings plankton closer to the larva where it is captured and digested, larval form was likely present in the common ancestor of lophotrochozoans, but has been lost.

Protostomes account for more than half of all described species, and most of those are ecdysozoans (which two groups?). Biologists like Terry Erwin estimate there are many, many more species that have not been described (ranging from 1 - 30 million).

the nematodes (~15k species) and arthropods (insects, chelicerata, crustaceans, and myriapods; ~800k species)

Describe the lifecycle peculiarities of the horsehair worms ("zombie worms"). This is a small sister clade of nematodes

there are *four* stages: the egg, pre-parasitic larva, parasitic larva, and free-living aquatic adult. After mating in spring, the female worm deposits a string of eggs 12 to 24 inches long in the water. About three weeks to one month later, minute immature larvae hatch. These larvae must parasitize an invertebrate host to develop. Suitable hosts for different species of horsehair worms include larger predaceous arthropods (often mantids, water beetles, carabid beetles, or dragonflies) or omnivores (such as crickets and other closely related insects, or millipedes).

Describe the nematodes: their cuticle, locomotion, size range, and distribution.

they are the most abundant animals on earth as far as the number of individuals. the *cuticle* is thick and multilayered which gives them an unsegmented shape. as it grows, it sheds the cuticle 4x where they exchange O2 and nutrients w/ the environment through the cuticle and gut wall. nematodes *move* by contracting their longitudinal muscles. nematodes are *microscopic* the largest being 9 meters. most live s scavengers at the bottom of the ocean.

We discussed 3 groups of worm-like, marine bottom dwellers in the ecdysozoan clade: priapulids, kinorhynchs, and loriciferens. What two traits do they all share, and what are the apparent consequences for the animals? Which group includes the a group of apparently anaerobic animals?

they share a thin cuticle for gas exchange which restricts them to moist habitats and get little support from the cuticle. loriciferens are anaerobic.