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The Learning Kingdom's Cool Fact of the Day for March 9, 1999
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What's the most primitive multicellular animal?
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In the animal kingdom, the most primitive multicellular forms are the
sponges, members of the phylum Porifera. These animals have been
around since just before the Cambrian Period, more than 500 million
years ago. Today there are about 5,000 known species of sponges.
All the cells of a sponge are nearly identical, and its body has no
distinct organs or separate tissues. It is a porous mesh of cells,
like a living filter, designed to trap tiny, floating life forms. It
does not move, but pulls water through itself, filtering out
microscopic life forms, which its cells engulf.
The simplest sponges can spontaneously reconstruct themselves after
being torn apart into individual cells. The cells move together and
build a body much like the old one, but with the individual cells in
different places.
More about sponges:
http://www.ucmp.berkeley.edu/porifera/porifera.html
Previous Cool Facts about very primitive life forms:
http://www.cool-fact.com/archive/1998/05/08.html
http://www.cool-fact.com/archive/1998/10/06.html
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