from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An organic cell or organized body that has independent movement within a living organism, especially a motile gamete such as a spermatozoon.
- n. An independent animallike organism produced asexually, as by budding or fission.
- n. One of the distinct individuals forming a colonial animal such as a bryozoan or hydrozoan.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An organic body or cell having locomotion, as a spermatic cell or spermatozoid.
- n. An animal in one of its inferior or early stages of development, as one of the intermediate forms in alternate generation.
- n. One of the individual animals in a composite group, as of Anthozoa, Hydroidea, and Bryozoa; — sometimes restricted to those individuals in which the mouth and digestive organs are not developed.
from the GNU version of the Collaborative International Dictionary of English
- adj. Pertaining to, or resembling, an animal.
- n. An organic body or cell having locomotion, as a spermatic cell or spermatozooid.
- n. An animal in one of its inferior stages of development, as one of the intermediate forms in alternate generation.
- n. One of the individual animals in a composite group, as of Anthozoa, Hydroidea, and Bryozoa; -- sometimes restricted to those individuals in which the mouth and digestive organs are not developed.
from The Century Dictionary and Cyclopedia
- Like an animal; of the nature of animals; having an animal character, form, aspect, or mode of existence, as an organism endowed with life and motion. See II.
- n. In biology, something like an animal; that which is of the nature of an animal, yet is not an animal in an ordinary sense, and is not the whole of an animal in a strict sense; one of the “persons” or recognizably distinct entities which compose a zoön; that product of any organism, whether of animal, vegetable, or equivocal character, which is capable of spontaneous movements, and hence may have an existence more or less apart from or independent of the parent organism.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. one of the distinct individuals forming a colonial animal such as a bryozoan or hydrozoan
Sorry, no etymologies found.
I'm not a biologist, but I do read that a zooid is a single cell that can move independently within a larger organism.
It is not easy to imagine two objects more widely different in appearance than a bristle or vibraculum, and an avicularium like the head of a bird; yet they are almost certainly homologous and have been developed from the same common source, namely a zooid with its cell.
It is interesting to see two such widely different organs developed from a common origin; and as the moveable lip of the cell serves as a protection to the zooid, there is no difficulty in believing that all the gradations, by which the lip became converted first into the lower mandible of an avicularium and then into an elongated bristle, likewise served as a protection in different ways and under different circumstances.
The vibracula may have been directly developed from the lips of the cells, without having passed through the avicularian stage; but it seems more probable that they have passed through this stage, as during the early stages of the transformation, the other parts of the cell with the included zooid could hardly have disappeared at once.
Mr. Busk, however, does not know of any gradations now existing between a zooid and an avicularium.
Such zooids are specialised to such an extent that they lack the structures associated with other functions and are therefore dependent for survival on the others to do what the particular zooid cannot do by itself.
1 Each such zooid in these pelagic colonial hydroids or hydrozoans has a high degree of specialization and, although structurally similar to other solitary animals, are all attached to each other and physiologically integrated rather than living independently.
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