The Animal Kingdom Heterotrophic by ingestion Motile; behaviorally complex No cell walls Structure based on extracellular proteins, especially collagen. Characteristic cell junctions. Similarities in ribosomal RNA

Evolutionary Trends in Body Plan Symmetry: None (sponges) Radial (jellyfish, sea stars) Bilateral (arthropods, vertebrates, etc.) Cephalization: Evolution of a “head” with sensory and feeding organs. Body cavities: Evolution of a true coelom lined with peritoneum.

Sponges – Phylum Porifera Simple body plan. Choanocytes beat their flagella to create water flow. Amoeboid cells feed by endocytosis.

Phylum Cnidaria Only two cell layers – acoelomate. Gastrovascular cavity (blind gut): opening acts as mouth and anus. Radial symmetry. Polyp and medusa body forms.

Classes of Cnidaria Hydrozoa: Hydra and its relatives Scyphozoa: jellyfish Anthozoa: sea anemones and corals.

Phylum Ctenophora – comb jellies Like Cnidaria but with a complete gut (mouth and anus)

Protostomes vs. Deuterostomes blastopore becomes the mouth ventral nerve cord(s) worms, insects, etc. Deuterostomes blastopore becomes the anus dorsal nerve cord sea stars, vertebrates

2 main groups of protostomes Lophotrochozoans – soft body, hydrostatic skeleton Ecdysozoans – exoskeleton that molts

Platyhelminthes – the flatworms simplest lophotrochozoans acoelomate gastrovascular cavity (blind gut)

Phylum Brachiopoda Marine animals with a 2-part shell, similar to bivalve mollusks. But they are NOT mollusks – they have a lophophore (ring of tentacles around the mouth. Few living species; diverse in the Paleozoic

Annelida – segmented worms True coelom Segmented body Soft flexible body wall.

Mollusca – the mollusks coelomate bilaterally symmetrical body plan based on muscular structure called a “foot” “visceral mass” – internal organs “mantle” – covers the visceral mass; secretes shell

Familiar mollusk groups Bivalves: 2-part shell (clams, oysters) Gastropods: snails, conchs, whelks, etc. Cephalopods: octopus and squid (internal shell)

Ecdysozoans – animals with exoskeletons

Nematoda - roundworms pseudocoelomate not an exoskeleton as such, but a thick cuticle that is shed as the animal grows.

Arthropods Chelicerata – spiders, mites, lice, scorpions Crustacea – shrimp, lobsters, crabs Uniramia – Myriopoda: centipedes and millipedes Insecta: insects