V - Zoological Terms

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vacuole

(L. vacuus, empty, + Fr. ole, dim.). A membrane-bound, fluid-filled space in a cell.

valence

(L. valere, to have power). Degree of combining power of an element as expressed by the number of atoms of hydrogen (or its equivalent) that the element can hold (if negative) or displace in a reaction (if positive). The oxidation state of an element in a compound. The number of electrons gained, shared, or lost by an atom when forming a bond with one or more other atoms.

valve

(L. valva, leaf of a double door). One of the two shells of a typical bivalve mollusc or brachiopod.

variation

(L. varius, various). Differences among individuals of a group or species that cannot be ascribed to age, sex, or position in the life cycle.

vector

(L. a bearer, carrier, from vehere, vectum, to carry). Any agent that carries and transmits pathogenic microorganisms from one host to another host. Also, in molecular biology, an agent such as bacteriophage or plasmid that carries recombinant DNA.

veins

(vanz) (L. vena, a vein). Blood vessels that carry blood toward the heart; in insects, fine extensions of the tracheal system that support the wings.

velarium

(L. velum, veil, covering). Shelf-like extension of thesubumbrella edge in cubozoans (phylum Cnidaria).

veliger

(L. velum, veil, covering). Larval form of certain molluscs; develops from the trochophore and has the beginning of a foot, mantle, shell, and so on.

velum

(L. veil, covering). A membrane on the subumbrella surface of jellyfish of class Hydrozoa. Also, a ciliated swimming organ of the veliger larva.

ventral

(L. venter, belly). Situated on the lower or abdominal surface.

venule

(L. venula, dim. of vena, vein). Small vessel conducting blood from capillaries to vein; small vein of insect wing.

vermiform

(L. vermis, worm, + forma, shape). Adjective to describe any wormlike organism; an adult (nematogen) rhombozoan (phylum Mesozoa).

vestige

(L. vestigium, footprint). A rudimentary organ that may have been well developed in some ancestor or in the embryo.

vibrissa

, pl. vibrissae (L. nostrilhair). Stiff hairs that grow from the nostrils or other parts of the face of many mammals and that serve as tactile organs; "whiskers".

vicariance

(L. vicarius, a substitute). Geographical separation of populations, especially as imposed by discontinuities in the physical environment that fragmented populations that were formerly geographically continuous.

villus

, pl. villi (L. tuft of hair). A small fingerlike, vascular process on the wall of the small intestine. Also one of the branching, vascular processes on the embryonic portion of the placenta.

virus

(L. slimy liquid, poison). A submicroscopic noncellular particle composed of a nucleoprotein core and a protein shell; parasitic; will grow and reproduce in a host cell.

viscera

(L. pl. of viscus, internal organ). Internal organs in the body cavity.

visceral

Pertaining to viscera.

vitalism

(L. vita, life). The discredited viewpoint that natural processes are controlled by supernatural forces and cannot be explained through the laws of physics and chemistry alone, as opposed to mechanism.

vitamin

(L. vita, life, + amine, from former supposed chemical origin). An organic substance required in small amounts for normal metabolic function; must be supplied in the diet or by intestinal flora because the organism cannot synthesize it.

vitellaria

(L. vitellus, yolk of an egg). Structures in many flatworms that produce vitelline cells, that is, cells that provide eggshell material and nutrient for the embryo.

vitelline gland

See vitellaria

vitelline membrane

(L. vitellus, yolk of an egg). The noncellular membrane that encloses the egg cell.

viviparity

(L. vivus, alive, + parere, to bring forth). Reproduction in which eggs develop within the female body, with nutritional aid of maternal parent as in therian mammals, many reptiles, and some fishes; offspring are born as juveniles. Adj., viviparous

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