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Chapter 32: An Overview of Animal Diversity

Term Definition

Animal multicellular, heterotrophic eukaryotes with tissuesthat develop from embryonic layers

Tissues groups of cells that have a common structure,function, or both; collections of specialized cellsisolated from other tisues by membranous layers

Cleavage rapid cell division undergone by the zygote after asperm fertilizes an egg

Blastula multicellular, hollow; formed from the cleavage

Gastrulation undergone by the blastula; forms a gastrulawithdifferent layers of embryonic tissues

Larva sexually immature and morphologically distinctfrom the adult; eventually undergoes

metamorphosisJuvenile resembles an adult, but is not yet sexually mature

Hox genes that regulate the development of body form;can produce a wide diversity of animalmorphology

Choanoflagellates may have resemblance to common ancestors ofliving animals; protists that are the closest livingrelatives of animals

Neoproterozoic Era (1 billion542 million years ago)

Ediacaran biota included in the early members of the animal fossilrecord; dates from 565 to 550 million years ago

Paleozoic Era (542251 million years ago)Cambrian explosion (535 to 525 million years ago) marks the earliest

fossil reappearance of many major groups of livinganimals

Several hypotheses regarding the cause of theCambrian explosion and decline of Ediacaranbiota:

- New predator-prey relationships- A rise in atmospheric oxygen-

The evolution of the Hox gene complex

Mesozoic Era (25165.5 million years ago) coral reefsemerged; ancestors of plesiosaurs were reptilesthat returned to the water; dinosaurs were thedominant terrestrial vertebrates; the first mammalsemerged; flowering plants and insects diversified

Cenozoic Era (65.5 million years ago to the present) beginningfollowed mass extinctions of both terrestrial andmarine animals which included the large, nonflyingdinosaurs and the marine reptiles; mammals

increased in size and exploited vacated ecologicalniches; global climate cooled

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Body plan a set of morphological and developmental traits

Radial symmetry no front and back, or left and right

Bilateral symmetry two-sided symmetry; often move actively andhave a central nervous system

Dorsal top

Ventral bottomAnterior head

Posterior tail

Cephalization development of a head

Sessile planktonic; drifiting or weakly swimming

Ectoderm germ layer covering the embryos surface

Endoderm innermost germ layer and lines the developingdigestive tube (archenteron)

Diploblastic have ectoderm and endoderm; include cnidariansand comb jellies

Triploblastic have an intervening mesodermlayer; include allbilaterans

Body cavity possessed by most triploblastic animals

Coelom a true body cavity; derived from mesoderm

Coelomates animals that possess a true coelom

Pseudocoelom a body cavity derived from mesoderm andendoderm

Pseudocoelomates triploblastic animals that possess apseudocoelom; belong to the same grade ascoelomates

Acoelomates triploblastic animals that lack a body cavity

Grade a group whose members share key biologicalfeatures; not necessarily a clade. An acestor andall of its descendants

Protostome development cleavage is spiraland determinate; splitting ofsolid masses of mesoderm forms the coelom

Deuterostome development Cleavage is radial and indeterminateeach cellin the early stages of cleavage retains thecapacity to develop into a complete embryo;makes possible identical twins, and embryonicstem cells; mesoderm buds from the wall of thearchenteron to form the coelom

Blastopore forms during gastrulation and connects thearchenteron to the exterior of the gastrula;becomes the mouthin protosome development;becomes the anusin deuterosome development

Eumetazoa a clade of animals with true tissues

Bilaterians most animal phyla belonging to the clade Bilateria;the morphology-based tree divides bilaterians intodeuterostomes and potostomes; molecular studiesindicate bilaterian clades Deuterostomia,Ecdysozoa, and Lophotrochozoa

Deuterostomia chordates and some other phylaEcdysozoans shed their exoskeleton through a process called

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