Term
|
Definition
| An integrated group of cells with a common structure, function, or both. |
|
|
Term
|
Definition
| The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote to a ball of cells. |
|
|
Term
|
Definition
| A hollow ball of cells that marks the end of the cleavage stage during early embryonic development in animals. |
|
|
Term
|
Definition
| An embryonic stage in animal development encompassing the formation of three layers: ectoderm, mesoderm, and endoderm. |
|
|
Term
|
Definition
| 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. |
|
|
Term
|
Definition
| A free-living, sexually immature form in some animal life cycles that may differ from the adult animal in morphology, nutrition, and habitat. |
|
|
Term
|
Definition
| A developmental transformation that turns an animal larva into either an adult or an adult-like stage that is not yet sexually mature. |
|
|
Term
|
Definition
| An early group of soft-bodied, multicellular eukaryotes known from fossils that range in age from 565 million to 550 million years old. |
|
|
Term
|
Definition
| A relatively brief time in geologic history when many present-day phyla of animals first appeared in the fossil record. This burst of evolutionary change occured about 535 - 525 million years ago and saw the emergence of the first large, hard-bodied animals. |
|
|
Term
|
Definition
| 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-image halves by any plane through its central axis. |
|
|
Term
|
Definition
| Body symmetry in which a central longitudinal plane divides into two equal but opposite halves. |
|
|
Term
|
Definition
| Pertaining to the top of an animal with radial or bilateral symmetry. |
|
|
Term
|
Definition
| Pertaining to the underside, or bottom, of an animal with radial or bilateral symmetry. |
|
|
Term
|
Definition
Pertaining to the front, or head, of a bilaterally symmetrical animal. |
|
|
Term
|
Definition
| Pertaining to the rear, or tail end, of a bilaterally symmetrical animal. |
|
|
Term
|
Definition
| An evolutionary trend toward the concentration of sensory equipment at the anterior end of the body. |
|
|
Term
|
Definition
| 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. |
|
|
Term
|
Definition
| 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 in species that have these structures. |
|
|
Term
|
Definition
|
|
Term
|
Definition
| The middle primary germ layer in a triploblastic animal embryo: develops into the notochord, the lining of the coelem, muscles, skeleton, gonads, kidneys, and most of the circulatory system in species that have these structures. |
|
|
Term
|
Definition
| Possessing three germ layers: the endoderm, mesoderm, and ectoderm. Most eumetazoans are triploblastic. |
|
|
Term
|
Definition
| An air-filled or fluid-filled space between the digestive tract and the body wall. |
|
|
Term
|
Definition
| A body cavity lined by tissue derived only from mesoderm. |
|
|
Term
|
Definition
| An animal that possesses a true coelem (a body cavity lined by tissue completely derived from mesoderm). |
|
|
Term
|
Definition
| An animal whose body cavity is lined by tissue derived from mesoderm and endoderm. |
|
|
Term
|
Definition
| A solid-bodied animal lacking a cavity between the gut and outer body wall. |
|
|
Term
|
Definition
| In animals, a developmental mode distinguished by the development of the mouth from the blastopore; often also characterized by spiral cleavage and by the body cavity forming when solid masses of mesoderm split. |
|
|
Term
|
Definition
| In animals, a developmental mode distinguished by the development of the anus from the blastopore; often also characterized by radial cleavage and by the body cavity forming as outpockets of mesodermal tissue. |
|
|
Term
|
Definition
| 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. |
|
|
Term
|
Definition
| A type of embryonic development in protostomes tht rigidly casts the developmental fate of each embryonic cell very early. |
|
|
Term
|
Definition
| 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. |
|
|
Term
|
Definition
| 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. |
|
|
Term
|
Definition
| The endoderm-lined cavity, formed during gastrulation, that develops into the digestive tract of an animal. |
|
|
Term
|
Definition
| In a gastrula, the opening of the archenteron that typically develops into the anus in deuterostomes and the mouth in protostomes. |
|
|
Term
|
Definition
| A clade of animals with true tissue. All animals except sponges and a few other groups are eumetazoans. |
|
|
Term
|
Definition
| A clade of animals with bilateral symmetry and three germ layers. |
|
|
Term
|
Definition
| A group of animal phyla identified as a clade by molecular evidence. Many ecdysozoans are molting animals. |
|
|
Term
|
Definition
| Members of a group of animal phyla identified as a clade by molecular evidence. Lophotrochozoans include organisms that have lophophores or trochophore larvae. |
|
|
Term
|
Definition
| In some lophotrochozoan animals, including brachiopods, a crown of ciliated tentacles that surround the mouth and function in feeding. |
|
|
Term
|
Definition
| Distinctive larval stage observed in some lophotrochozoan animals, including some annelids molluscs. |
|
|
