Chapter 32: An Introduction To Animal Diversity

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anterior

Back 1

Pertaining to the front, or head, of a bilaterally symmetrical animal.

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archenteron

Back 2

The endoderm-lined cavity, formed during gastrulation, that develops into the digestive tract of an animal.

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arthropod

Back 3

A segmented ecdysozoan with a hard exoskeleton and jointed appendages. Familiar examples include insects, spiders, millipedes, and crabs.

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bilateral symmetry

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Body symmetry in which a central longitudinal plane divides the body into two equal but opposite halves.

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bilaterian

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Member of a clade of animals with bilateral symmetry and three germ layers.

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blastopore

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In a gastrula, the opening of the archenteronthat typically develops into the anus in deuterostomes and the mouth in protostomes.

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blastula

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A hollow ball of cells that marks the end of the cleavage stage during early embryonic development in animals.

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body cavity

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A fluid- or air-filled space between the digestive tract and the body wall.

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body plan

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In animals, a set of morphological and developmental traits that are integrated into a functional whole—the living animal.

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Cambrian explosion

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A relatively brief time in geologic history when large, hard-bodied forms of animals with most of the major body plans known today appeared in the fossil record. This burst of evolutionary change occurred about 535–525 million years ago.

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cell wall

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A protective layer external to the plasma membrane in the cells of plants, prokaryotes, fungi, and some protists. Polysaccharides such as cellulose (in plants and some protists), chitin (in fungi), and peptidoglycan (in bacteria) are an important structural component of cell walls.

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cephalization

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An evolutionary trend toward the concentration of sensory equipment at the anterior end of the body.

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chordate

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Member of the phylum Chordata, animals that at some point during their development have a notochord

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clade

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A group of species that includes an ancestral species and all its descendants

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cleavage

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(1) The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. (2) The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote to a ball of cells.

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coelom

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A body cavity lined by tissue derived only from mesoderm.

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coelomate

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An animal that possesses a true coelom (a body cavity lined by tissue completely derived from mesoderm).

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determinate cleavage

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A type of embryonic development in protostomes that rigidly casts the developmental fate of each embryonic cell very early.

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deuterostome development

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n animals, a developmental mode distinguished by the development of the anus from the blastopore

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diploblastic

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Having two germ layers.

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ecdysozoans

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Member of a group of animal phyla identified as a clade by molecular evidence. Many ecdysozoans are molting animals.

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ectoderm

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The outermost of the three primary germ layers in animal embryos

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endoderm

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The innermost of the three primary germ layers in animal embryos

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Eukarya

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The domain that includes all eukaryotic organisms.

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eumetazoan

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Member of a clade of animals with true tissues. All animals except sponges and a few other groups are eumetazoans.

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gastrula

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An embryonic stage in animal development encompassing the formation of three layers: ectoderm, mesoderm, and endoderm.

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gastrulation

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In animal development, a series of cell and tissue movements in which the blastula-stage embryo folds inward, producing a three-layered embryo, the gastrula.

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grade

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A group of organisms that share the same level of organizational complexity or share a key adaptation.

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heterotroph

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An organism that obtains organic food molecules by eating other organisms or substances derived from them.

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larva

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(plural, larvae) A free-living, sexually immature form in some animal life cycles that may differ from the adult animal in morphology, nutrition, and habitat.

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lophophore

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In some lophotrochozoan animals, including brachiopods, a crown of ciliated tentacles that surround the mouth and function in feeding.

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lophotrochozoan

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Member of a group of animal phyla identified as a clade by molecular evidence. Lophotrochozoans include organisms that have lophophores or trochophore larvae.

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mesoderm

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The middle primary germ layer in an animal embryo

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metamorphosis

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A developmental transformation that turns an animal larva into either an adult or an adult-like stage that is not yet sexually mature.

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molting

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A process in ecdysozoans in which the exoskeleton is shed at intervals, allowing growth by the production of a larger exoskeleton.

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protostome development

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In animals, a developmental mode distinguished by the development of the mouth from the blastopore

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pseudocoelomate

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An animal whose body cavity is lined by tissue derived from mesoderm and endoderm.

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radial cleavage

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A type of embryonic development in deuterostomes in which the planes of cell division that transform the zygote into a ball of cells are either parallel or perpendicular to the vertical axis of the embryo, thereby aligning tiers of cells one above the other.

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radial symmetry

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Symmetry in which the body is shaped like a pie or barrel (lacking a left side and a right side) and can be divided into mirror-imaged halves by any plane through its central axis.

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spiral cleavage

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A type of embryonic development in protostomes in which the planes of cell division that transform the zygote into a ball of cells are diagonal to the vertical axis of the embryo. As a result, the cells of each tier sit in the grooves between cells of adjacent tiers.

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triploblastic

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Possessing three germ layers: the endoderm, mesoderm, and ectoderm. Most eumetazoans are triploblastic.

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a

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without

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koilos

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a hollow (acoelomate: the condition of lacking a coelom)

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arch

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ancient, beginning (archenteron: the endoderm-lined cavity, formed during the gastrulation process, that develops into the digestive tract of an animal)

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bi

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two (Bilateria: the branch of eumetazoans possessing bilateral symmetry)

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blast

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bud, sprout

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pore

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a passage (blastopore: the opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes)

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cephal

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head (cephalization: an evolutionary trend toward the concentration of sensory equipment on the anterior end of the body)

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deutero

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second (deuterostome: one of two lines of coelomates characterized by radial, indeterminate cleavage, formation of the coelom from outpockets of mesoderm, and development of the anus from the blastopore)

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di

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two (diploblastic: having two germ layers)

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ecdys

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an escape (Ecdysozoa: one of two proposed clades within the protostomes

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ecto

Back 52

outside

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derm

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skin (ectoderm: the outermost of the three primary germ layers in animal embryos)

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endo

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within (endoderm: the innermost of the three primary germ layers in animal embryos)

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gastro

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stomach, belly (gastrulation: the formation of a gastrula from a blastula)

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in

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into

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gest

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carried (ingestion: a heterotrophic mode of nutrition in which other organisms or detritus are eaten whole or in pieces)

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lopho

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a crest, tuft

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trocho

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a wheel (Lophotrochozoa: one of two proposed clades within the protostomes that includes annelids and molluscs)

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meso

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middle (mesoderm: the middle primary germ layer of an early embryo)

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meta

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boundary, turning point

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morph

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form (metamorphosis: the resurgence of development in an animal larva that transforms it into a sexually mature adult)

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proto

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first

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stoma

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mouth (protostomes: a member of one of two distinct evolutionary lines of coelo-mates characterized by spiral, determinate cleavage, formation of the coelom as splits in solid masses of mesoderm, and development of the mouth from the blastopore)

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pseudo

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false (pseudocoelom: a body cavity that is not completely lined by mesoderm)

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radia

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a spoke, ray (radial symmetry: characterizing a body shaped like a pie or barrel, lacking a left and right side, but having a top and bottom)

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tri

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three (triploblastic: having three germ layers)