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| Referring to the head end of a bilaterally symmetrical animal. |
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| The endoderm-lined cavity, formed during the gastrulation process, that develops into the digestive tract of an animal. |
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| Characterizing a body form with a central longitudinal plane that divides the body into two equal but opposite halves. |
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| The opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes. |
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| The hollow ball of cells marking the end stage of cleavage during early embryonic development. |
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| A fluid-containing space between the digestive tract and the body wall. |
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| 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. |
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| An evolutionary trend toward the concentration of sensory equipment on the anterior end of the body. |
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| 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. |
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| A body cavity completely lined with mesoderm. |
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| In animals, a developmental mode distinguished by the development of the mouth from the blastpore; often also characterized by schizocoelous development of the body cavity and by spiral cleavage. |
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| Pertaining to the back of a bilaterally symmetrical animal. |
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| Member of a group of animal phyla with protostome development that some systematists hypothesize form a clade, including many molting animals. |
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| 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. |
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| 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. |
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| The three-layered, cup-shaped embryonic stage. |
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| The formation of a gastrula from a blastula. |
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| Three main layers that form the various tissues and organs of an animal body. |
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| A heterotrophic mode of nutrition in which other organisms or detritus are eaten whole or in pieces. |
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| (plural, larvae) A free-living, sexually immature form in some animal life cycles that may differ from the adult in morphology, nutrition, and habitat. |
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| A horseshoe-shaped or circular fold of the body wall bearing ciliated tentacles that surround the mouth. |
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| 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. |
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| The resurgence of development in an animal larva that transforms it into a sexually mature adult. |
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| Animal belonging to a grade of organization lacking true tissues (collections of specialized cells isolated from other tissues by membranes); a sponge (phylum Porifera). |
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| Pertaining to the rear, or tail, of a bilaterally symmetrical animal. |
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| 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. |
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| An animal whose body cavity is not completely lined by mesoderm. |
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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 polar axis, thereby aligning tiers of cells one above the other. |
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| 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. |
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Definition
| 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. |
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Definition
| Possessing three germ layers: the endoderm, mesoderm, and ectoderm. Most eumetazoans are triploblastic. |
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| Distinctive larval stage observed in annelids and molluscs. |
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| Pertaining to the underside, or bottom, of a bilaterally symmetrical animal. |
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