Saturday, March 24, 2007

Annelids: The segmented worms

The bristle worm’s hollow bristles are reported to be venomous. Stings may result in intense skin swelling, with a burning sensation or numbness. The bristles can penetrate thin gloves, so these worms should be handled carefully or, more appropriately, not at all.

Annelids have bodies that are segmented. Within the body of the segmented worm are rather elaborate and well developed systems of organs. There is a circulatory system with five "aortic arches" which act as a heart to keep the blood moving in the worm. There is a digestive tract that begins with a prostomium with a mouth, a muscular pharynx, an esophagus, a crop for storage of food, a gizzard for breaking food down (much as a stomach acts in humans) and a small intestine where the nutrients are absorbed into the blood for delivery to cells. There is a small brain on the dorsal side of the pharynx that connects to the ventral nerve cord that runs the length of the worm. Worms are hermaphroditic (have the organs that produce eggs and others which produce sperm). Earthworms have a clitellum that slips off of the worm and becomes a brood chamber for developing young.
1.) What are a few common members of this group?
2.) What do leaches commonly eat?