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CHAPTER 30: ANIMALS: PART I
30.1 Evolutionary Trends Among Animals
Animals are extremely diverse, but in general they are heterotrophic, typically have
the power of movement or locomotion by means of muscle fibers, are
multicellular, have a life cycle in which the adult is typically diploid, and undergo
sexual reproduction and produce an embryo that goes through development stages.
All but one of the 30 animal phyla is invertebrates. Only one phylum contains
vertebrates.
Anatomical Data
Refer to Figure 30.2.
Type of Symmetry
Animals can be asymmetrical, radially symmetrical, or bilaterally
symmetrical.
Embryonic Development
Sponges have the cellular level of organization. True tissues appear in
the other animals as they undergo embryological development. Some
animals have two germ layers (ectoderm and endoderm), while some
have three (ectoderm, endoderm, and mesoderm). Animals with three
germ layers are either protostomes or deuterostomes.
30.2 Introducing the Invertebrates
Sponges
Sponges are aquatic. They are multicellular but lack organized tissues. They
are filter
feeders. Sponges can reproduce both asexually and sexually.
Cnidarians
Cnidarians are multicellular, tubular, or bell-shaped animals that reside
mainly in shallow coastal waters. They are radially symmetrical and have true
tissues.
Cnidarian Diversity
Examples of cnidarians include sea anemone, coral, hydrozoans, and
jellyfish.
Hydra
Hydra is a freshwater cnidarian. It has a sac body plan. It has two
tissue layers:
ectoderm and endoderm.
30.3 The Trochozoa
The trochozoa are bilaterally symmetrical at least in some stage of their
development. As embryos, they have three germ layers, and as adults, they have
the organ level of organization. Trochozoans are protostomes and include the
trochophores, which either have a trochophore larva today or an ancestor with one
in the past.