Download key terms lab 9

KEY TERMS FOR LAB EXERCISE 9:
Acoelomate. A solid-bodied animal lacking a cavity between the gut and outer
body wall.
Agnathan. A member of a jawless class of vertebrates represented today by the
lampreys and hagfishes.
Anterior. Referring to the head e nd of a bilaterally symmetrical animal.
bilateral symmetry. Characterizing a body form with a central longitudinal plane
that divides the body into two equal but opposite halves.
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.
Cephalization. An evolutionary trend toward the concentration of sensory
equipment on the anterior end of the body.
Chordate. A member of a diverse phylum of animals that possess a notochord; a
dorsal, hollow nerve cord; pharyngeal gill slits; and a postanal tail as an embryo.
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.
Closed circulatory system. Circulatory systems in which blood is confined to
vessels and is kept separate from the interstitial fluid.
Coelom. A body cavity completely lined with mesoderm.
Coelomate. An animal whose body cavity is completely lined by mesoderm, the
layers of which connect dorsally and ventrally to form mesenteries.
Determinate cleavage. A type of embryonic development in protostomes that
rigidly casts the developmental fate of each embryonic cell very early.
Deuterostomes. One of two distinct evolutionary lines of coelomates, consisting
of the echinoderms and chordates and characterized by radial, indeterminate
cleavage, enterocoelous formation of the coelom, and development of the anus
from the blastopore.
Dioecious. Organisms having only a single set of reproductive organs.
Diploblastic. Having two germ layers.
Dorsal. Pertaining to the back of a bilaterally symmetrical animal.
Echinoderms. Sessile or slow-moving animals that include sea stars, sea
urchins, brittle stars, crinoids, and basket stars.
Exoskeleton. A hard encasement on the surface of an animal, such as the shells
of mollusks or the cuticles of arthropods, that provides protection and points of
attachment for muscles.
Endoskeleton. Internal skeleton composed of calcium carbonate plates just
beneath the surface of the skin.
Hydrostatic skeleton. A skeletal system composed of fluid held under pressure
in a closed body compartment; the main skeleton of most cnidarians, flatworms,
nematodes, and annelids.
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.
Monoecious. Organisms contain both male and female reproductive organs
within the same individual.
Open circulatory system. An arrangement of internal transport in which blood
bathes the organs directly and there is no distinction between blood and
interstitial fluid.
Posterior. Pertaining to the rear, or tail, of a bilaterally symmetrical animal.
Protostome. A member of one of two distinct evolutionary lines of coelomates,
consisting of the annelids, mollusks, and arthropods, and characterized by spiral,
determinate cleavage, schizocoelous formation of the coelom, and development
of the mouth from the blastopore.
Pseudocoelom. A body cavity that is not completely lined by tissue derived from
mesoderm.
Pseudocoelomate. An animal whose body cavity is not completely lined by
mesoderm.
Radial cleavage. A type of embryonic development in deuterostomes in that 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.
Radula. A straplike rasping organ used by many mollusks during feeding.
Segmentation. Segmented animals have repeating units. This has led to
specialization of parts over evolutionary time because the different segments
could become specialized for different purposes.
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: the endoderm, mesoderm, and
ectoderm. Most eumetazoa are triploblastic.
Ventral. Pertaining to the underside, or bottom, of a bilaterally symmetrical
animal.
Water vascular system. A network of hydraulic canals unique to echinoderms
that branches into extensions called tube feet, which function in locomotion,
feeding, and gas exchange.