Annelida phylum

Introduction to the Annelida

Segmented worms make up the Phylum Annelida. The phylum includes earthworms and their relatives, leeches, and a large number of mostly marine worms known as polychaetes. Various species of polychaete are known as lugworms, clam worms, bristleworms, fire worms, sea mice, and "EWWW! I stepped on that THING!"

Everybody's favorite, worms. . .

An Annelid Worm Biodiversity List  is available, with links to a large number of annelid-related resources of all sorts. It also includes subscription information on the ANNELIDA e-mailing list.Annelids can be told by their segmented bodies. Polychaetes (meaning "many bristles") have, predictably, many bristles on the body, while earthworms and leeches have fewer bristles. There are about 9000 species of annelid known today.Serious annelid connoisseurs should not miss the Biodiversity and Biological Collections Web Server . Those interested in vermiculture might prefer The Burrow , a remarkably designed Website with abundant information on earthworm farming. And not to forget the third main class of annelids, Mark Siddal's Hirudinea pages present original work on the evolution of leeches.

Annelids probably originated in the Precambrian. Indeed, a few Vendian fossils, such as Spriggina, were once assigned to the Annelida; however, this identification is now doubted. Definite annelids appeared in the Cambrian. Pictured above is Canadia, from the Middle Cambrian Burgess Shale of British Columbia.
Canadia and other Cambrian polychaetes had no jaws, but some later polychaetes developed hard jaws, which are sometimes mineralized with iron oxide. Such polychaete jaws are fairly common in the fossil record, and are known as scolecodonts.
Body fossils of polychaetes are rarer, being generally restricted to Lagerstatten - localities with unusually good preservation of fossils. Mazon Creek, near downtown Chicago, is one of these localities where polychaetes have been found. Fossil oligochaetes are much rarer, and there are almost no fossil hirudineans (leeches) known.