Biology: Animal Diversity: Invertebrates

CH 24: ANIMAL DIVERSITY I: INVERTEBRATES
What are the key features of animals?
Animals characteristics:

 Eukaryotes
 Multicellular
 Lack a cell wall
 Heterotrophic
 Sexual reproduction
 Mobile
 Rapid external stimuli response


Which anatomical features mark branch points on the animal evolutionary tree?

 Lack of tissues in sponges sets them apart from other animals (early history)
o In sponges, independent cells have specialized functions (not forming tissues)
 Animals with tissues exhibit radial or bilateral symmetry
o Radial (cnidarians: sea jellies, corals, anemones & ctenophores: come jellies)
 Sessile: fixed in one spot
 2 embryonic germ layers (tissue layers)
 Endoderm: produce inner germ layer lining the gut
 Ectoderm: produce outer layer covering outside the body
 bisected into 2 equal halves (lacking well defined head) (don’t matter
how bisected)
o Bilateral:(remaining phyla with anterior head and posterior tail)
 Motile: move under their own power
 bisected into mirror images
 evolution accompanies by cephalization: concentration of sensory organs
and brain in a well-defined head)
 3 embryonic germ layers
 Endoderm:
o produce inner germ layer lining the gut
o differentiates to form tissues lining respiratory surfaces,
the gut, hollow organs
 Ectoderm:
o produce outer layer covering outside the body
o Forms nerve tissue and tissues on outer surface of body
 Mesoderm:
o lies between the endoderm and ectoderm