Ch 32 Ap Bio

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acoelomates

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An animal that lacks a coelom. Acoelomates, which include the flatworm, fluke, tapeworm, and ribbon worm, exhibit bilateral symmetry and possess one internal space, the digestive cavity.

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anterior

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of or near the head end or toward the front plane of the body

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archenteron

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The central cavity of the gastrula, which ultimately becomes the intestinal or digestive cavity.

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bilateral symmetry

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Symmetrical arrangement, as of an organism or a body part, along a central axis, so that the body is divided into equivalent right and left halves by only one plane.

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bilateria

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Group of animals with bilateral symmetry

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blastopore

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The opening into the archenteron formed by the invagination of the blastula to form a gastrula.

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blastula

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An early embryonic form produced by cleavage of a fertilized ovum and consisting of a spherical layer of cells surrounding a fluid-filled cavity

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Cambrian explosion

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Seemingly rapid appearance of most major groups of complex animals around 530 million years ago, as evidenced by the fossil record.

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cephalization

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An evolutionary trend in the animal kingdom toward centralization of neural and sensory organs in the head or anterior region of the body.

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cleavage

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The series of mitotic cell divisions that produces a blastula from a fertilized ovum. It is the basis of the multicellularity of complex organisms

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coelomates

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Group of animals (metazoans above the lower worms) with a usually epithelium-lined body cavity that forms a large space when well developed between the digestive tract and the body wall

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determinate cleavage

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cleavage of an egg in which each division irreversibly separates portions of the zygote with specific potencies for further development

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deuterostomes

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Broad classification of organisms distinguished by their embryonic development; namely the first opening (the blastopore) becomes the anus

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diploblastic

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Derived from two embryonic germ layers, the ectoderm and the endoderm. Lacks true mesoderm.

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dorsal

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belonging to or on or near the back or upper surface of an animal or organ or part;

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ectoderm

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The outermost of the three primary germ layers of an embryo, from which the epidermis, nervous tissue, and, in vertebrates, sense organs develop.

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Ediacaran period

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a late Precambrian period of geological time, before the Cambrian Period to 635 million years ago. Simple, soft bodied fossils of multicellular organisms

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endoderm

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The innermost of the three primary germ layers of an animal embryo, developing into the gastrointestinal tract, the lungs, and associated structures. Also called hypoblast.

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enterocoelous

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The coelom formed from a pocketlike outgrowth of the wall of the archenteron (digestive tract), especially in echinoderms and chordates.

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eumetazoa

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A subdivision of the animal kingdom that includes all multicellular animal organisms having cells that are differentiated and form tissues and organs.

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gastrulation

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the process in which a gastrula develops from a blastula by the inward migration of cells

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germ layers

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Any of three cellular layers, the ectoderm, endoderm, or mesoderm, into which most animal embryos differentiate and from which the organs and tissues of the body develop through further differentiation.

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indeterminate cleavage

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cleavage in which all the early divisions produce blastomeres with the potencies of the entire zygote

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ingestion

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To take into the body by the mouth for digestion, absorption, or endocytosis

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larva

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The newly hatched, earliest stage of any of various animals that undergo metamorphosis, differing markedly in form and appearance from the adult.

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mesoderm

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The middle embryonic germ layer, lying between the ectoderm and the endoderm, from which connective tissue, muscle, bone, and the urogenital and circulatory systems develop.

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metamorphosis

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A change in the form and often habits of an animal during normal development after the embryonic stage.

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parazoa

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multicellular organisms having less-specialized cells than in the Metazoa; comprises the single phylum Porifera

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posterior

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at or near the hind end in quadrupeds or toward the spine in primates

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protostomes

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broad classification of organisms that tend to share certain embryological traits; among these the formation of the "mouth first" (hence the name) during gastrulation, before the future anus. (The site of gastrulation initiation, the blastopore, becomes the mouth.)

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pseudocoelomates

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Group of animals haning an internal body cavity of some primitive invertebrates, similar to a coelom but lacking a mesodermal lining.

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radial cleavage

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Characteristic of deuterostomes where cell division changes it from a four-cell embryo to an eight-cell embryo, the cells divide such that each cell in the top four cell plane is directly over one other cell in the bottom plane.

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radial symmetry

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Organism stape resembling a pie, where several cutting planes produce roughly identical pieces.

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radiata

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The radially symmetric animals of the Eumetazoa subregnum

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schizocoelous

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A coelom which arises by a splitting of the mesoblast of the embryo.

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spiral cleavage

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Characteristic of protostomes where cell division changes it from a four-cell embryo to an eight-cell embryo, the cells divide such that each cell in the top four cell plane is at an angle to the opposite cell in the bottom plane.

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triploblastic

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Having three germ layers. Used of the vertebrate embryo.

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ventral

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toward or on or near the belly (front of a primate or lower surface of a lower animal)