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Six hundred million years ago, during the evolution of animals, there were three primary habitats for animal life--the open sea, the surface of the sea floor, and the soft muddy substrate there. Some of the earliest animals burrowed in the soft sea floor mud. They were segmented worms, as shown by fossil worm tracks, dated to Edicacaran times (540-650). Descendants of these earliest worms can be found today living in the muddy substrate of the quiet bays--members of the Phylum Annelida, 'Annelid' means ring, or or segmented--a characterstic that separates these worms from other animal phyla. Inside the body shows repetition of organs and body parts, with the intestine and main blood vessels passing through segments. |
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