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Discover the fascinating characteristics and evolutionary trends of the diverse animal groups, from simple sponges to complex cephalopods. Learn about body plans, symmetry, and unique features like nematocysts and lophophores.
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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. • Digestive system: • Ingestion into individual cells (sponges) • Gastrovascular cavity (blind sac) (jellyfish) • Digestive tract with mouth & anus (most other groups) • 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. • Also review pores, osculum, and spicules
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 • Anthozoa: sea anemones and corals (lack medusa) • Hydrozoa: Hydra and Portuguese man-of-war (colonial) • Scyphozoa: jellyfish (medusa dominates life cycle)
Portuguese Man-of-WarColonial hydrozoan, with stinging structures called nematocysts
Phylum Ctenophora – comb jellies • Like Cnidaria but with a complete gut (mouth and anus)
Protostomes vs. Deuterostomes • Protostomes: • 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
Rotifers – small, structurally complex(complete digestive tract, ciliated structures)
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)
