Symmetry

Body Cavity

Stages of Animal Evolution

Sponges – Phylum Porifera Sessile – does not move Mostly marine Multicellular – but has no tissues No body symmetry Gets nutrients through pores

Sponges

Sponge Anatomy

Phylum Cnidaria – stinging animals Soft bodies with tentacles and stinging cells Radial symmetry One opening - both mouth and anus Nerve net Two cell layers – ectoderm and mesoderm Polyp and medusa Hydra, jelly fish, sea anemone

Cnidarians

Cnidarian Anatomy

Tentacles

Phylum Platyhelminthes - Flatworms Flat bodies with bilateral symmetry Nerve ladder with brain 3 cell layers – ectoderm, mesoderm and endoderm Mostly parasitic One opening Planaria, flukes, tapeworms

Tapeworm

Planarian

Phylum Rotifera Very small Pseudocoelom Crown of cilia for feeding

Phylum Nematoda - Roundworms Bilateral symmetry Tough outer covering - cuticle Digestive cavity Can be parasites First to have body cavity – pseudocoelom Ex. Roundworms, pinworms, heartworms

Nematodes

Phylum Annelida – Segmented Worms Ringlike segmented bodies Bilateral symmetry Tubelike digestive tract Organ systems Setae on segments Dorsal vein Ventral nervous system True Coelom Ex. Earthworms, leeches

Annelids

Annelids

Phylum Mollusca – Soft bodied invertebrates Soft bodies with shells Move with muscular foot Have a mantle that secretes the shell Bilateral symmetry True Coelom 6. 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 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