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-War
Colonial 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)
Ecdysozoans – animals with exoskeletons
or tough cuticle