The Evolution The Evolution of Animal of Animal DiversityDiversity

What Characteristic Define an AnimalWhat Characteristic Define an Animal?

• EukaryotEukaryotic cellsic cells

• MulticellularMulticellular

• Ingestive HeterotrophIngestive Heterotroph

Other Common Characteristics of AnimalsOther Common Characteristics of Animals

• Lack cell wallsLack cell walls

• Sexual reproductionSexual reproduction

• Diploid, except for gametesDiploid, except for gametes

• Excitable (nervous & muscular) tissueExcitable (nervous & muscular) tissue

• Similar embryology (blastula & gastrula)Similar embryology (blastula & gastrula)

Early embryonic developmentEarly embryonic development

Early embryonic developmentEarly embryonic development

gastrulationgastrulationgastrulagastrula

blastula

Animal Diversity

How did the animal kingdom evolve?How did the animal kingdom evolve?

- Oldest fossils are 700 million years old- Oldest fossils are 700 million years old

-Animals probably evolved from an ancestor Animals probably evolved from an ancestor of a colonial choanoflagellateof a colonial choanoflagellateprotistprotist

One hypothesis for the origin of One hypothesis for the origin of animalsanimals

Major Trends in Animal Evolution:Major Trends in Animal Evolution:

• Development of Tissue LayersDevelopment of Tissue Layers

• Patterns of Body SymmetryPatterns of Body Symmetry

• Development of a Body CavityDevelopment of a Body Cavity

• Body SegmentationBody Segmentation

Development of Tissue LayersDevelopment of Tissue Layers

Most animals have tissues that arise from Most animals have tissues that arise from three embryologic tissues layers:three embryologic tissues layers:

• EctodermEctoderm – produce skin and nervous – produce skin and nervous systemsystem

• EndodermEndoderm – produces GI tract – produces GI tract

• MesodermMesoderm – produces muscle, skeleton and – produces muscle, skeleton and most organsmost organs

Major Trends in Animal Evolution:

Three embryologic tissue layersThree embryologic tissue layers

EctodermEctoderm EndodermEndoderm

MesodermMesoderm

Major Trends in Animal Evolution:

Patterns of Body SymmetryPatterns of Body Symmetry

• AsymmetricalAsymmetrical

• Bilateral symmetryBilateral symmetry

• Radial symmetryRadial symmetry

Body symmetryBody symmetry

Bilateral = a Bilateral = a cut through cut through main body main body axis produces axis produces right-left right-left halveshalves

Radial = any cut Radial = any cut through main through main body axis body axis produces mirror produces mirror image halvesimage halves

Major Trends in Animal Evolution:

Development of a Body Cavity:Development of a Body Cavity:

• Allows independent movement of body Allows independent movement of body wall wall

• Cushions internal organsCushions internal organs

• Provides a hydrostatic skeleton Provides a hydrostatic skeleton

• Increases flexibility and mobilityIncreases flexibility and mobility

Major Trends in Animal Evolution:

Development of a Body Cavity:Development of a Body Cavity:

• CoelomateCoelomate – true body cavity fully lined – true body cavity fully lined with mesodermwith mesoderm

• PseudocoelomatePseudocoelomate – body cavity in direct – body cavity in direct contact with gutcontact with gut

• AcoelomateAcoelomate – lack body cavity – lack body cavity

CoelomateCoelomate

PseudocoelomatePseudocoelomate

AcoelomateAcoelomate

Coelomates: Protostomes VS DeuterostomesCoelomates: Protostomes VS Deuterostomes

ProtostomesProtostomes: : mesoderm forms mesoderm forms from mass of cells from mass of cells between endoderm between endoderm and ectodermand ectoderm

DeuterostomesDeuterostomes: : mesoderm forms as mesoderm forms as outpocketing of outpocketing of gastrulation cavitygastrulation cavity

ProtostomesProtostomes DeuterostomesDeuterostomes

Visualizing Protostome & Deuterostome Development

Major Trends in Animal Evolution:

Body SegmentationBody Segmentation

• Most animals have segmented bodiesMost animals have segmented bodies

• Segmentation increases body flexibility Segmentation increases body flexibility and mobilityand mobility

Forms of asexual reproduction

• fission: splitting off of new individual from existing one, parent cell divides into two parts

• budding: new individual grows from body of original, can detach (solitary lifestyle) or remain attached (colonial lifestyle)

• fragmentation: breaking of the body into several pieces, each of which forms a complete adult (aka regeneration)

• gemmulation: release of specialized groups of cells that are enclosed in a capsule and grow into new individuals

Sexual Reproduction• Two haploid gametes (produced by meiosis) fuse to

form a diploid zygote.• female gamete = ovum = unfertilized egg; usually large

and non-motile cell.• male gamete = spermatozoan = small, usually

flagellated cell.• Fertilization occurs in two ways:

– external fertilization -eggs & spermatozoa are shed into the environment.

– internal fertilization -sperm are deposited or near the female’s reproductive tract and egg and sperm unite within the female’s body.

PhylogeneticPhylogenetictree of Kingdomtree of KingdomAnimaliaAnimalia

Phylum Porifera: SpongesPhylum Porifera: Sponges

Probably first animals to evolve – similar to Probably first animals to evolve – similar to modern colonial choanoflagellate protistmodern colonial choanoflagellate protist

Early embryonic developmentEarly embryonic development

What was the distinguishing What was the distinguishing characteristic that differentiated a true characteristic that differentiated a true multicellular organism and a colonial multicellular organism and a colonial

protist?protist?

Sponges have Sponges have specialized cellsspecialized cells that exhibit that exhibit cellular recognition cellular recognition but lack true tissue layersbut lack true tissue layers

ChoanocytesChoanocytes – specialized – specialized for obtaining foodfor obtaining food

AmeobocytesAmeobocytes- - specialized for digestion,specialized for digestion,nutrient transport, waste nutrient transport, waste disposal, skeletal componentdisposal, skeletal componentmanufacure. Can change into manufacure. Can change into other cell types. other cell types.

Epithelial cells

Noncellularmesoglea andskeletal components

Osculum

Porocyte cell

Anatomy of a Sponge

Sponges can reproduce sexually or asexuallySponges can reproduce sexually or asexually

Sponges are hermaphrodites, producing both sperm and eggs.

Motile sponge larvaMotile sponge larva

Newly settled spongeNewly settled sponge

Sexual ReproductionSexual Reproduction

Asexual Sponge ReproductionAsexual Sponge Reproduction

1. Budding1. Budding 2. Gemmules2. Gemmules

Sponge Reproduction

Sponge Classes

• Demospongae (spongin)

• Calcarea (Ca)

• Hexactinella (Si)

1. Evolution of 1. Evolution of tissue layerstissue layers

Major Trends in Animal Evolution:

Phylum Cnidaria Coelenterata)Phylum Cnidaria Coelenterata)::

HydraHydra JelliesJellies

AnemonesAnemones Corals

Phylum Cnidaria Characteristics:• Radial symmetry

• True tissue layers (but only 2, not 3)

• Cnidocytes/nematocysts (stinging cells) for prey capture

• Gastrula stage of development

• Digestive (gastrovascular) cavity• Diversity of Living Things: Phylum Cnidaria• Phylum Cnidaria (Jellyfish, Sea Anemones, Corals, Sea Combs)• Phylum Cnidaria: The Stinging Animals

• Nerve Net, with nerve cells, but not centralization/brain

• Excretion of water through specialzed cells

• Both extracellular and intracellular digestion

• One opening -2 way digestive system

• Dioecious

• Planula/ciliated larvae

Arms & Camp, 1995

Radial symmetryRadial symmetry

Radial symmetry allows a Radial symmetry allows a sessile animal to meet its sessile animal to meet its

environment equally from all environment equally from all sidessides

Early embryonic developmentEarly embryonic development

gastrulationgastrulationgastrulagastrula

blastula

Polyp and medusa forms of cnidariansPolyp and medusa forms of cnidarians

PolypPolyp

MedusaMedusa

Purves et al., 1992

Cnidocytes and nematocystsCnidocytes and nematocysts

Brum et al., 1994

Firing Nematocysts

For anemones and corals:

For jellies and hydra:

A comparison of poriferans & cnidarians

Coral reefs have enormous biodiversity.

Zooxanthellae

Cnidarian Classes• Hydrozoa fresh water hydras• Anthozoa sea anemones, corals• Siphonphora Portuguese Man-A-War• Scyphozoa jellyfish

Life Cycle of a Cnidarian

Jellyfish, Coral Feeding, Coral Spawning, 2, Moon jelly

Ctenophora“comb jellies” “sea walnuts”

• Radially symmetrical w/ mesoglea

• Eight rows/ “combs” of banded cilia that propel

• No polyp stage

• Hermaphroditic

Major Trends in Animal Evolution:

1.1. Evolution of Evolution of tissue layerstissue layers

2. Evolution of 2. Evolution of bilateral bilateral symmetrysymmetry

Bilateral symmetryBilateral symmetry

Arms & Camp, 1995

CephalizationCephalization: : evolutionary trend toward evolutionary trend toward concentration of sensory concentration of sensory structures at the anterior structures at the anterior endend

Only one plane of symmetry Only one plane of symmetry that produces mirror-image that produces mirror-image halveshalves

• Triploblastic- 3 embryonic layers

• Ectoderm- skin, nervous structures

• Endoderm- digestive tract, reproductive

• Mesoderm - muscles, skeleton, body systems

Hallmark characteristics of flatworms:Hallmark characteristics of flatworms:

• Three tissue layersThree tissue layers

• Acoelomates – solid bodies without a body Acoelomates – solid bodies without a body cavitycavity

• Bilateral symmetryBilateral symmetry

Phylum Platyhelminthes  flat, thin body and there are no spaces between tissue layers

therefore no cell is far from the environment, diffusion for circulation and respiration

  most primitive animals w/ bilateral symmetry

  bilateral symmetry allow for further specialization w/ a dorsal and ventral end, anterior and posterior end, allows organism to respond more immediately to environment

  "brain"-collection of nerve cells at anterior end• "cephalization" tendency towards brain formations • Kingdom Animalia: Phylum Platyhelminthes• Phylum platyhelminthes: The Flatworms

AcoelomatesAcoelomates

Turbellaria(free-living flatworms)

Walls, 1982Phylum Platyhelminthes: flat wormsPhylum Platyhelminthes: flat worms

Cestoda(tapeworms)

Trematoda(flukes)Walls, 1982

Solomon et al., 1996

Class Turbellaria:• free living, planarians• eyespot, cilia over body surface• predatory/saprophytic• one digestive opening located ventrally medial, extendable

pharynx attached to mouth• branched digestive tract/glands• sexual and asexual reproduction: hermaphroditic &

regeneration• flame cells for water excretion & nitrogenous wastes• 2 main nerves w/ side braches• no resp sys, gas exchange through surface and environment • Basic Anatomy of a Planarian

Internal anatomy of free-living Internal anatomy of free-living Planaria Planaria fflat wormlat worm

Arms & Camp, 1995

Gastrovascular cavity

Class Trematoda: Flukes

• VD.LS.4.11.14516 Life Cycle• -internal/external parasites• -attach to host w/suckers• -protective cuticle• -asexual reproduction of larvae in snail• -sexual reproduction of fluke in sheep• -have a digestive system • Blood Fluke Life Cycle

Figure 33.10  The life history of a blood fluke (Schistosoma mansoni)

Trematoda-parasitic flukes

Endo-parasites of vertebrates, have at least 2 hosts (complicated life cycles)

Blood fluke -get from being in water with snails and sewage

Liver fluke- if eat uncooked fish

Lung fluke-if eat uncooked crab

Class Cestoda: Tapeworms

• no brain or "head"• scolex (w/ hooks & suckers) for attaching to

intestine• self reproduction organs (hermaphroditic)• repeating units called proglottids• larva consumed by 1st host, encyst in muscle, 2nd

host consumes muscle & adult form in • intestinal tract

Endoparasites of vertebrates.

Head region (scolex) is modified for attachment inside intestine.

No digestive system

Proglottids produce male and female gametes at same time, create fertilized eggs that pass out with feces.

Host gets infected by eating food contaminated with eggs, (or putting contanimated fingers in mouth).

Cestoda-tapeworms

Major Trends in Animal Evolution:

1.1. Evolution of Evolution of tissue layerstissue layers

2. Evolution of 2. Evolution of bilateral bilateral symmetrysymmetry

3. Development of 3. Development of a pseudocoeloma pseudocoelom

Phylum Nematoda: roundwormsPhylum Nematoda: roundworms

Animations:Animations:

Intestinal Worms, , Schistomasis Filariasis,,

Videos:Videos:

Filiarasis, , Threadworms

Hallmark characteristics of roundworms:Hallmark characteristics of roundworms:

• Three tissue layersThree tissue layers

• Bilateral symmetryBilateral symmetry

• PseudocoelomPseudocoelom

• Complete digestive tract – one way passage of Complete digestive tract – one way passage of nutrients from mouth to anusnutrients from mouth to anus

Major Trends in Animal Evolution:

1.1. Evolution of tissue Evolution of tissue layerslayers

2. Evolution of 2. Evolution of bilateral symmetrybilateral symmetry

3. Development of a 3. Development of a pseudocoelompseudocoelom

4. Development of a 4. Development of a true body cavity: true body cavity: coelomcoelom

CoelomateCoelomate

PseudocoelomatePseudocoelomate

What the significance of coelom lined with What the significance of coelom lined with mesoderm?mesoderm?

Phylum Mollusca: Soft Bodied Animals Head/foot w/ sensory and motor organs Visceral mass w/ well developed organs of digestion, excretion and

reproduction Mantle which encloses visceral mass and secretes the shell Respire through gills & mantle Radula is a movable tooth like chitinous strip CaCO3 shell 3 chambered heart, open circ system• siphon • N wastes removed through nephridia • Kingdom Animalia: Phylum Mollusca• Phylum Mollusca (Mollusks) • Mollusks : Mollusks, such as squids and octopuses are explored in this video

segment. • Visualizing Movement in Mollusks • Mollusks Facts and Fun

Phylum MolluscaPhylum Mollusca

gastropods

pelecypodspelecypodscephalopods

All mollusks have a similar body plan:All mollusks have a similar body plan:

Class Gastropoda• univalves; snail & slugs, abalones, limpets Feeding

Gastropod VD.LS.4.11.20156 Radula, octopus• mantle which secreted shell (layer of cells)• radula, rasping feeding device• muscular foot• gills for gas exchange w/i mantle which absorbs O2 from H2O• land varieties can have a lung• open circulatory system, tissues bathed in blood

Hemocyanin=blue• trochophore larvae • Leopard Slug Mating , Nudibranch

Class Pelecypoda

• bivalves: clams, mussels, oysters, scallops

• no radula• have 2 shells controlled by

adductor and abductor muscles

• incurrent and excurrent siphon

Not Just for Chowder

Class Cephalopoda• octopus, squid, nautilus,

cuttlefish• shell b/co internal (xcept

nautilus)• foot evolves into flexible

arms• closed circulatory system

for more efficient travel to muscles

• siphon used in locomotionOctopus Camouflage 2Mimic Octopus Octopus Hatching & Learning Giant Squid

Development of Development of segmentationsegmentation

Major Trends in Animal Evolution:

Phylum AnnelidaPhylum Annelida

Earthworms- Earthworms- terrestrial worm terrestrial worm movement

Polychaetes – Polychaetes – marine segmented marine segmented worms worms swimming

LeechesLeeches

Segmentation:Segmentation:

The combination of a true coelom that acts as The combination of a true coelom that acts as a hydrostatic skeleton and segmentation a hydrostatic skeleton and segmentation allows for controlled directed movements.allows for controlled directed movements.

• A skeleton gives muscles something to A skeleton gives muscles something to contract against and allows coordinated contract against and allows coordinated movement.movement.

• Segmented circular muscles along with Segmented circular muscles along with longitudinally directed muscles allows for longitudinally directed muscles allows for forward directed movements.forward directed movements.

Phylum Annelida   Coelomate: w/ all organs suspended in the body cavity by

an attached membrane “peritoneum”   Have a closed circulatory system w/5 hearts which pump

blood through ventral vessel and blood returns to heart through dorsal blood vessel

  Segmented repeating body parts: metamerism evolutionary advantage: an animals can increase in size by adding segments and the segments can become specialized

 Locomotion through unsegmented body parts• Body= respiratory surface (can use gills) • Earthworm Systems • Ecological Importance of Annelids

Class Polychaetes(greatest variety in annelids)

• Marine, can reach up to 3 meter VD.LS.4.11.16756 Sand Mason Worm

• can be free moving or sedentary• Can have antennae and jaws• Have parapodia w/ setae

VD.LS.3.20.36231 Sea Mouse• can have external gills• Peritoneum-mem. from inner

mesoderm holding organism place

• Trochophore larvae: w/ apical tuft, girdle of cilia and mouth

• Marine Worms, Plumed Worm

Class Oligochaetes

• Digestion: food, mouth, pharynx, crop, gizzard, intestine

• Excretion: anus and nephridia for N wastes

• Locomotion: muscle groups & 2 prs or 4 setae per segment, also to grip earth

• Reproduction: hermaphroditic, clitellum

Class Hirudinea

• leechesVD,LS.4.12.23455

Locomotion• Free living and parasitic• Parasitic species have

rasping teeth• secrete hirudin, an

anticoagulant NOVA Now Leeches Giant Leech

Development of Development of jointed appendagesjointed appendages

Major Trends in Animal Evolution:

Phylum ArthropodaPhylum Arthropoda::

Arthropod =Arthropod =

““jointed foot”jointed foot”

Jointed appendages and Jointed appendages and a hard a hard exoskeletonexoskeleton has has made arthropods the made arthropods the most successful phyla most successful phyla of animals.of animals.

Exoskeleton• chitinous exoskeleton (a cuticle

secreted by underlying epidermis that contains chitin) chitin is a polysacchride also found in the cell walls of fungi

• the exoskeleton serves as an armor to protect the soft body of the insect, as well as to aid in mobility

• this outside skeleton must be shed periodically as the athropod grow the shedding is called “ecdysis”

External skeleton made of chitin allowed the External skeleton made of chitin allowed the arthropods to inhabit the land:arthropods to inhabit the land:

• protectionprotection

• waterproofingwaterproofing

• anchor site for attachment of musclesanchor site for attachment of muscles

Disadvantage of an exoskeleton :Disadvantage of an exoskeleton :

• most be shed to allow growth (molt) most be shed to allow growth (molt)

• restricts movements around jointsrestricts movements around joints

• limits ultimate size of the organism (heavy)limits ultimate size of the organism (heavy)

Metamorphosis• growth accompanied by ecdysis

(molting) of the exoskeleton, can become 33% larger than before the shed

• Can grow by complete or incomplete metamorphosis

• Butterfly emerging

Complete Metamorphosis

Incomplete Metamorphosis

Introduction to Arthropods   arthro-joint pes-foot (greek)   largest phylum, most successful & ubiquitous, 3x's all other

animals species   coelomate   exoskeleton w/ chitinous (polysaccharide) plates & hinges

which must be shed  muscles attached to inner exoskeleton   molting necessary, many larval stages, complete &

incomplete metamorphosis  loss of metamerism: segments fused   segmental structures (appendages) b/co struct & fnctally diff.Arthropods Videos

  modified head, thorax and abdomen (cephalothorax)

  nervous sys. w/ dorsal ant. brain -> ventral nerve cord w/ ganglionic swellings in each segment

 open circ system, tissues bathed in blood

 dioecious

• 5 senses: compound & simple eyes, taste, smell through pheromones, touch, hearing

Horseshoe crab, Limulus polyphemus

Solomon et al., 1996

Emperor scorpion, Pandinis imperator

Phylum Arthropoda: Phylum Arthropoda: Subphylum: Subphylum: Chelicerata

House dust mite, Dermatophagoides sp.

Orb spider, Araneus quadratus

Pink fairy crab David Doubilet; National Geographic, Jan 1999

Krill

http://members.aol.com/iq3d2/deep_sea/Hi_Res/Krill.jpg

Gooseneck barnacle

Brum et al., 1994

Mantis shrimp larva

Phylum Arthropoda: Phylum Arthropoda: Subphyla Aquatic MandibulatesSubphyla Aquatic Mandibulates Class: Class: Crustacea

Subphyla Aquatic Mandibulates Class Crustacea

• Carapace that covers head and thorax, 6 segments in abdomen

• Respires through gills

• N wastes excreted through green gland

• crayfish, crabs, lobsters, shrimp, Daphnia, pillbugs, barnacles, prawns

Potter 1982

Greater stag beetle, Lucanus cervus

Insecta

Uniramia

Phylum Arthropoda:Phylum Arthropoda:

Diplopods: Millipede

Chilopods: House centipede, Scutigera coleoptera

Potter 1982

Praying mantis

Campbell et al., 1999

Subphyla Terrestrial Madibulates/Myriapods

Class Diplopoda

• "millipedes"

• range from 2mm - 28cm

• have mandibles for chewing decaying vegetation

• 2 pairs of legs per segment adapted for burrowing

Subphyla Terrestrial Madibulates/Myriapods

Class Chilopoda• "centipedes"

• range from 3-30cm

• have fangs, are predacious carnivores some species consume frogs, birds snakes and mice

• 1 pair of legs per segment, adapted for running

• appendages on last segment used for defense not locomotion

Insecta• Insecta 70% of all animals on earth 30 orders:

– Diptera:“2 wings”flies, gnats, mosquitoes– Coleoptera: “shield wings”beetles– Hymenoptera: “membrane wing”bees, wasps, ants– Lepidoptera: “scale wing” moths & butterflies

• 3 Body Sections• 3 prs of legs per thorax• 1 pr antennnae• excrete N through Malpighian tubules eliminated in dry uric acid

crystals• respire through tracheae and spiracles• Complete & Incomplete Metamorphosis• Parthenogenesis

Harmful Insects• Pests, vectors of pathogens, crop

eaters, sting, bite

Botfly, , Bed Bugs

Beneficial Insects• Pollination, honey, silk, food

(entomophagy), biological control, designer genes

Eating Machines

Medicinal Maggots

Forensic Entomology

Crime Scene Creatures

Development of a Development of a body cavity from body cavity from the gastrulation the gastrulation cavity: cavity: deuterostome deuterostome coelomatescoelomates

Major Trends in Animal Evolution:

ProtostomesProtostomes DeuterostomesDeuterostomes

Coelomates: Protostomes VS DeuterostomesCoelomates: Protostomes VS Deuterostomes

ProtostomesProtostomes: : mesoderm forms mesoderm forms from mass of cells from mass of cells between endoderm between endoderm and ectodermand ectoderm

DeuterostomesDeuterostomes: : mesoderm forms as mesoderm forms as outpocketing of outpocketing of gastrulation cavitygastrulation cavity

• Deuterostomes (echinoderms and chordates) develop the anus first, then the mouth at the other end of the embryo. Deuterostomes are coelomate animals these embryological characteristics:– Radial cleavage in embryonic cell division: the daughter cells sit on top of

previous cells. – Fate of cells is indeterminate; if embryonic cells are separated, each one

develops a complete organism. – The blastopore is associated with the anus, and the second embryonic opening is

associated with the mouth.

Phylum EchinodermataPhylum Echinodermata

Sea LilySea urchin

Brittle starSea star

Echinoderms:Echinoderms:

• All are marine organismsAll are marine organisms

• Larvae are bilaterally symmetricalLarvae are bilaterally symmetrical

• Adults are slow moving or sessile and have Adults are slow moving or sessile and have have petamerous radial symmetry (although have petamerous radial symmetry (although they are not perfectly symmetrical)they are not perfectly symmetrical)

• Embryologic development makes them more Embryologic development makes them more similar to chordates than to the cnidarianssimilar to chordates than to the cnidarians

• Visualizing an Echinoderm Visualizing an Echinoderm

• Unique to echinoderms is the water vascular system, a network of hydraulic canals branching into extensions called tube feet.– These function in locomotion, feeding, and gas exchange.

Echinos=spiny Derma=skinEchinoderms include : sea star, sea urchin, sea cucumber,

sand dollar, basket stars brittle starsmarine & largely bottom dwellers pentamerous radial symmetry, from bilateral ancestor  internal skeleton w/calcareous ossicle that may articulate,

bears projecting spines/tubercles series of canals, water vascular system no excretory organs• mostly dioecious w/ external fertilization • Fertilization in a Sea Urchin

Echinoderm Classes • Asteroidea: star shaped, free moving, with bodies

composed of rays• Ophiuroidea: basket stars, serpents stars, brittle stars• Echinoidea: sea urchins, sand dollars

– Fertilization

• Holothuroidea: sea cucumber (anus)• Crinoidea: Sea lillies, feather stars• Colentricycloidea: sea daisies • Classes of Echinoderms • Sea cucumber Fights with Guts

CoelomatesCoelomates

PseudocoelomatesPseudocoelomatesAcoelomatesAcoelomates

Protostomes Deuterostomes

Brum et al., 1994

Bilateral symmetryBilateral symmetry

Primitive Chordates

• Anatomy of a Tunicate

References• http://cas.bellarmine.edu/tietjen/images/phylum_porifera.htm

• http://www.cartage.org.lb/en/themes/sciences/Zoology/Biologicaldiverstity/AnimalsII/AnimalsII.htm

• Parasites How They Live

• Invertebrates Close Up

• Animals webpage