Symmetry

Body Cavity

Stages of Animal Evolution

Sponges – Phylum Porifera

1. Sessile – does not move2. Mostly marine3. Multicellular – but has no tissues4. No body symmetry5. Gets nutrients through pores

Sponges

Sponge Anatomy

Phylum Cnidaria – stinging animals

1. Soft bodies with tentacles and stinging cells2. Radial symmetry3. One opening - both mouth and anus4. Nerve net5. Two cell layers – ectoderm and mesoderm6. Polyp and medusa7. Hydra, jelly fish, sea anemone

Cnidarians

Cnidarian Anatomy

Tentacles

Phylum Platyhelminthes - Flatworms

1. Flat bodies with bilateral symmetry2. Nerve ladder with brain3. 3 cell layers – ectoderm, mesoderm and

endoderm4. Mostly parasitic5. One opening 6. Planaria, flukes, tapeworms

Tapeworm

Planarian

Phylum Rotifera

• Very small• Pseudocoelom• Crown of cilia for feeding

Phylum Nematoda - Roundworms

1. Bilateral symmetry2. Tough outer covering - cuticle3. Digestive cavity4. Can be parasites5. First to have body cavity – pseudocoelom6. Ex. Roundworms, pinworms, heartworms

Nematodes

Phylum Annelida – Segmented Worms

1. Ringlike segmented bodies2. Bilateral symmetry3. Tubelike digestive tract4. Organ systems5. Setae on segments6. Dorsal vein7. Ventral nervous system8. True Coelom9. Ex. Earthworms, leeches

Annelids

Annelids

Phylum Mollusca – Soft bodied invertebrates

1. Soft bodies with shells2. Move with muscular foot3. Have a mantle that secretes the shell4. Bilateral symmetry5. True Coelom6. Ex. Clams, scallops, squid, octopus, snails,

slugs

Bivalves

Clam anatomy

Gastropods

Cephalopods

Phylum Arthropoda - Insects

• Segmented• Jointed Appendages• Exoskeleton made of Chitin• Head, thorax, abdomen• Crustaceans – crabs, lobster, shrimps• Millipedes and Centipedes• Insects

Crustaceans

Insects

Metamorphosis

Echinoderms

• Deuterostome development – blastopore becomes the anus

• Star fish, brittle stars, sea urchin

Sea Star

Echinoderms

Protostome and deuterostome development

• Protostomes – determinate cleavage where early cells have predetermined fate

• Deuterostomes – indeterminate cleavage where early cells can be the whole organism

Phylum Chordata

• Notochord, dorsal hollow nerve cord• Gill slits• Deuterostome development• Vertebrates, lancelets, tunicates

Lancelets

Tunicate

Classes within Cnidaria

Cnidaria• Hydrozoa – Hydra – alternates between

medusa and polyp• Scyphozoa – medusa more prevalent• Anthozoa – sea anemones, coral (calcified

skeleton)• Ctenophora – comb jellies

Classes within Platyhelminthes

• Turbellaria – planarians – free-living, marine• Trematoda – flukes - parasitic• Cestoidea – tapeworms – parasitic

Classes within Annelida

• Oligocheata – earthworms• Polychaeta – marine worms• Hirudinea - leeches

Classes within Arthropoda

• Arachnida – spiders• Diplopoda – millipedes• Chilopoda – centipedes• Insecta – insects• Crustacea – lobsters, crayfish, crabs, shrimp

Classes within Echinodermata

• Asteroidea – sea stars• Ophiuroidea – brittle stars• Echinoidea – sand dollar, sea urchin• Holothuroidea - sea cucumbers

Evolution of segmentation

• Arthropods and annelids had a shared ancestor, but maybe not as close as once thought.

• Hox genes in segmented animals will determine which organs will develop in each segment