from Wiktionary, Creative Commons Attribution/Share-Alike License
- proper n. A taxonomic subkingdom within the kingdom Animalia — the metazoa.
from the GNU version of the Collaborative International Dictionary of English
- n.pl. 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.
from The Century Dictionary and Cyclopedia
- 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.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. multicellular animals having cells differentiated into tissues and organs and usually a digestive cavity and nervous system
Sorry, no etymologies found.
You didn't answer this question, but said that molecular homology does indicate vertical descent (common ancestry from an actual cell) in Metazoa, “the group located above the Darwinian threshold.”
"Planula" theory, according to which the ancestral form of the Metazoa was a two-layered closed sac formed typically by delamination, less often by invagination.
The album, "Metazoa," was recorded with and produced by Billy Anderson (NEUROSIS, MELVINS, SLEEP, PRIMORDIAL), mixed by Anderson, and mastered by Justin Weis (HAMMERS OF MISFORTUNE, LUDICRA, SLOUGH FEG).
Current revision as of 06: 20, 8 February 2010 taxonomic Kingdom Animalia (also called Metazoa heterotrophs (i.e. they rely directly or indirectly on other organisms for their nourishment).
I then would run my ancestry lines from Chordata (3) down to Metazoa (2) and from Metazoa to the ground line (1).
Of course, above the level of the domains, Woese's thinking is (more or less) conventional evolution — the vertical descent of familiar monophyletic groups (the eukaryotes, the Metazoa, etc).
We can repeat the exercise if you like for Metazoa, Chordata, etc.
You then cited publications where Woese, Doolittle, and others, affirm their faith in the monophyly of Eukarya, Metazoa, chimps and humans, whatever.
Michael Sherman's Universal Genome in the Origin of Metazoa proposes an experimentally testable hypothesis and a model with two major predictions appearing in the linked abstract:
As to why sexual selection is important, then just consider the evolutionary history of the Metazoa and Metaphyta.