| Term | Definition |
|---|
| acoelomate | A solid-bodied animal lacking a cavity between the gut and outer body wall |
| anterior | The head of a bilaterally symmetrical animal |
| archentron | The endoderm-lined cavity, formed during the gastrulation process, that develops into the digestive tract of an animal |
| bilateral symmetry | Characterizing a body form with a central longitudinal plane that divides the body into two equal but opposite halves |
| bilaterian | Member of the clade Bilateria, animals with bilateral symmetry |
| blastopore | The opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes |
| blastula | The hollow ball of cells marking the end stage of cleavage during early embryonic development |
| body cavity | A fluid-containing space between the digestive tract and the body wall |
| body plan | In animals, the set of morphological and developmental traits that define a grade |
| Cambrian explosion | A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively brief time in geologic history; recorded in the fossil record about 545–525 million years ago |
| cephalization | An evolutionary trend toward the concentration of sensory equipment on the anterior end of the body |
| cleavage | The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane; specifically, the succession of rapid cell divisions without growth during early embryonic development that converts the zygote into a ball of cells |
| coelom | A body cavity completely lined with mesoderm |
| coelomate | Animal that possesses a true coelom |
| determinate cleavage | A type of embryonic development in protostomes that rigidly casts the developmental fate of each embryonic cell very early |
| protostome development | In animals, a developmental mode distinguished by the development of the mouth from the blastopore; often also characterized by schizocoelous development of the body cavity and by spiral cleavage |
| diploblastic | Having two germ layers |
| dorsal | Pertaining to the back of a bilaterally symmetrical animal |
| ecdysozoan | Member of a group of animal phyla with protostome development that some systematists hypothesize form a clade, including many molting animals |
| ectoderm | The outermost of the three primary germ layers in animal embryos; gives rise to the outer covering and, in some phyla, the nervous system, inner ear, and lens of the eye |
| Ediacaran fauna | Earliest generally accepted animal fossils, dating from about 575 million years ago |
| endoderm | The innermost of the three primary germ layers in animal embryos; lines the archenteron and gives rise to the liver, pancreas, lungs, and the lining of the digestive tract |
| enterocoelous | Pattern of formation of the body cavity common in deuterostome development, in which the mesoderm buds from the wall of the archenteron and hollows, forming the body cavity |
| eumetazoan | Member of the clade Eumetazoa, animals with true tissues (all animals except sponges) |
| gastrula | The three-layered, cup-shaped embryonic stage |
| gastrulation | The formation of a gastrula from a blastula |
| germ layers | Three main layers of an animal |
| grade | Group of animal species that share the same level of organizational complexity |
| indeterminate cleavage | A type of embryonic development in deuterostomes, in which each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo |
| larva | A free-living, sexually immature form in some animal life cycles that may differ from the adult in morphology, nutrition, and habitat |
| lophopore | A horseshoe-shaped or circular fold of the body wall bearing ciliated tentacles that surround the mouth |
| lophotrochozoan | Member of a group of animal phyla with protostome development that some systematists hypothesize form a clade, characterized by lophophores or trochophore larvae |
| mesoderm | The middle primary germ layer of an early embryo that develops into the notochord, the lining of the coelom, muscles, skeleton, gonads, kidneys, and most of the circulatory system |
| metamorphosis | The resurgence of development in an animal larva that transforms it into a sexually mature adult |
| parazoan | Animal belonging to a grade of organization lacking true tissues (collections of specialized cells isolated from other tissues by membranes); a sponge (phylum Porifera) |
| posterior | Pertaining to the rear, or tail, of a bilaterally symmetrical animal |
| deuterostome development | In animals, a developmental mode distinguished by the development of the anus from the blastopore; often also characterized by enterocoelous development of the body cavity and by radial cleavage |
| pseudocoelomate | An animal whose body cavity is not completely lined by mesoderm |
| radial cleavage | 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 polar axis, thereby aligning tiers of cells one above the other |
| radial symmetry | Characterizing a body shaped like a pie or barrel, with many equal parts radiating outward like the spokes of a wheel; present in cnidarians and echinoderms |
| schizocoelous | Pattern of formation of the body cavity common in protostome development, in which initially solid masses of mesoderm split, forming the body cavity |
| spiral cleavage | A type of embryonic development in protostomes, in which the planes of cell division that transform the zygote into a ball of cells occur obliquely to the polar axis, resulting in cells of each tier sitting in the grooves between cells of adjacent tiers |
| triploblastic | Possessing three germ layers |
| trochophore larva | Distinctive larval stage observed in annelids and molluscs |
| ventral | Pertaining to the underside, or bottom, of a bilaterally symmetrical animal |
Combine with other sets
Share on Facebook
Share on MySpace