Metazoa

Definitions

  • WordNet 3.6
    • n Metazoa multicellular animals having cells differentiated into tissues and organs and usually a digestive cavity and nervous system
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Webster's Revised Unabridged Dictionary
    • n. pl Metazoa (Zoöl) Those animals in which the protoplasmic mass, constituting the egg, is converted into a multitude of cells, which are metamorphosed into the tissues of the body. A central cavity is commonly developed, and the cells around it are at first arranged in two layers, -- the ectoderm and endoderm. The group comprises nearly all animals except the Protozoa.
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Century Dictionary and Cyclopedia
    • Metazoa All those animals which are above the Protozoa, and which in the course of their development undergo certain metamorphoses, consisting of the primary segmentation of a true egg or ovum, and the subsequent passage through an embryonic condition in which they possess at least two distinct germinal layers: animals exhibiting cellular differentiation. The Metazoa are distinguished from the Protozoa in that the substance of the body is differentiated into histogenic elements—that is to say, into cells. In all the Metazoa the ovum has the form of a nucleated cell, the first step in the process of development being the production of a blastoderm by the subdivision of that cell, the cells of the blastoderm giving rise in turn to two layers of cells, endoderm and ectoderm, between which, in most cases, a mesoderm appears, to be itself split in two layers; such a four-layered germ developing finally all the histological elements of the adult body. With the exception of certain parasites, and the extremely modified males of a few species, all these animals possess a permanent alimentary cavity lined by a special layer of endodermal cells. Sexual reproduction is the rule, and very generally the male element has the form of filiform spermatozoa. The lowest term in the series of the Metazoa is represented by the Porifera or sponges. Those of the Metazoa which possess a notochord, and in the adult state have the trunk divided into segments or myotomes, constitute the subkingdom Vertebrata; the rest are the several subkingdoms of invertebrates. Compare Protozoa. See Mesozoa, and cuts under gastrudation.
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Chambers's Twentieth Century Dictionary
    • n.pl Metazoa met-a-zō′a many-celled animals possessing cellular differentiation
    • Metazoa opp. to single-celled Protozoa
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Etymology

Webster's Revised Unabridged Dictionary
NL., fr. Gr. after + zo^,on an animal

Usage

In literature:

The gastrula stage was the palingenetic repetition of the ancestral form of all Metazoa, the Gastraea.
"Form and Function" by E. S. (Edward Stuart) Russell
How do protozoa differ from higher animals (metazoa) as regards (a) structure, (b) reproduction?
"Text Book of Biology, Part 1: Vertebrata" by H. G. Wells
The whole of the animal kingdom is divided into two great groups, which are called the Protozoa and the Metazoa.
"Darwin, and After Darwin (Vol. 1 and 3, of 3)" by George John Romanes
The parasites found in the bowel belong principally to two natural groups, Protozoa and Metazoa.
"Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 4" by Various
The phylum Porifera or Spongiae includes the simplest of the Metazoa or multicellular animals.
"Freshwater Sponges, Hydroids & Polyzoa" by Nelson Annandale
The Metazoa thus include Grades II., III., and IV.
"Stories of the Universe: Animal Life" by B. Lindsay
A considerable number of early developmental processes are common to the whole of the Metazoa.
"The Works of Francis Maitland Balfour, Volume 1" by Francis Maitland Balfour
The one-celled animals are called Protozoa, and the many-celled animals Metazoa.
"Elementary Zoology, Second Edition" by Vernon L. Kellogg
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