Chapter 32 - An Introduction to Animal Diversity

Animals

multicellular, heterotrophic eukaryotes that ingest food, have nervous and muscle tissue for movement and signal conduction, supported by collagen instead of cell walls, mostly reproduce sexually, diploid stage dominates

Hox genes

regulatory genes unique to animals that control expression of other genes influencing morphology

Last common ancestor of animals

flagellated protists (choanoflagellates)

Cleavage

succession of cell divisions in the zygote without growth between divisions

Blastula

hollow ball of cells formed by cleavage

Gastrulation

process where the blastula forms a gastrula with different embryonic tissue layers; evolutionary trait unique to animals

Larva

juvenile stage distinct in appearance from adult

Metamorphosis

transformation from larva to adult

Ectoderm

outer germ layer covering embryo, gives rise to nervous system and epidermis (skin)

Endoderm

innermost germ layer lining the developing digestive tube (archenteron), gives rise to digestive organs and lining

Mesoderm

intervening germ layer, gives rise to muscles, connective tissue, bone, cartilage, blood, and associated organs

Diploblastic animals

animals with two germ layers: ectoderm and endoderm (e.g., cnidarians)

Triploblastic animals

animals with three germ layers: ectoderm, mesoderm, endoderm; includes all bilaterians

Acoelomate

triploblastic animal that lacks a body cavity; three layers form a solid mass

Coelomate

animal with a true body cavity completely lined by mesoderm

Pseudocoelomate

animal with a body cavity derived from both mesoderm and endoderm; cavity partially lined

Advantages of fluid-filled body cavity

cushions and protects internal organs; acts as hydrostatic skeleton; allows organs to move and grow independently of body wall

Symmetry

categorization of animals based on body organization

Asymmetry

animals with no particular symmetry (e.g., sponges)

Radial symmetry

body arranged around a central axis, multiple planes of symmetry, usually sessile or drifting (e.g., starfish)

Bilateral symmetry

body with right and left sides, anterior and posterior, dorsal and ventral; enables cephalization (head formation) and directional movement

Cephalization

concentration of sensory organs at the anterior end, forming a head and brain

Protostome development

spiral and determinate cleavage; blastopore becomes mouth

Deuterostome development

radial and indeterminate cleavage; blastopore becomes anus; second opening forms mouth; includes echinoderms and chordates

Parazoa

sponges; lack true tissues

Eumetazoa

all animals with true tissues except sponges

Metazoa

all animals with tissues

Bilateria

animals with bilateral symmetry and three germ layers

Major bilaterian clades

Deuterostomia, Ecdysozoa, Lophotrochozoa

Deuterostomia

may include invertebrates or vertebrates; blastopore becomes anus; radial cleavage

Ecdysozoa

animals that molt a cuticle (ecdysis); includes arthropods and nematodes

Lophotrochozoa

includes ectoprocts, molluscs, and annelids

Fertilization

fusion of sperm and egg forming a diploid zygote

Development

series of events: fertilization > cleavage > blastula > gastrula > larva > metamorphosis > adult