Class Polychaeta

1. Metamerically segmented.
2. Bilateral symmetry.
3. Chitinous setae called parapodia.
4. Schizocoelic.
5. Closed circulatory system.
6. Complete digestive system.
7. Respiration through skin, gills or parapodia.
8. Nephridia for excretion.
9. Hermaphroditic, asexual reproduction in some by budding.

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   Description:
   Polychaetes, or marine worms, live under rocks, in coral crevices, in abandoned shells or burrow into the mud or sand. Some build their own sheltering tubes made from bottom debris. A significant part of marine food chains, they are eaten by fish, crustaceans and many others. Polychaetes differ from other annelids in having a well differentiated head with specialized sense organs and no clitellum. They have many setae, usually arranged in bundles on the parapodia. The head bears eyes, antennae, and sensory palps. The sense organs in polychaetes are more highly developed than in oligochaetes. In contrast to clitellates, polychaetes have no permanent sex organs, possess no permanent ducts for their sex cells and usually have separate sexes. Some polychaetes are free moving pelagic forms, some are active burrowers and crawlers, and some are sedentary, living in tubes or burrows. Most sedentary dwellers are particle feeders, using ciliary or mucoid methods of obtaining food. Their principal food source is plankton and detritus.

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   Some Interesting Facts:
   
   • The polychaetes are the largest and most primitive class of annelids, with more than 5300 described species, most of them marine.
   • Although the majority are from 5 to 10 cm long, some are less than a millimeter, and others may be as long as 3 meters.
   • Some are brightly colored in reds and greens; others are dull or iridescent.

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   Lab Directions: Specimens available are:
   • Nereis: the clamworm, slide of parapodium and preserved
   • Arenicola: the lugworm, preserved specimens
   • Aphrodite: the sea mouse, preserved specimens
   
   As always make a small sketch of the whole specimens. For your detailed sketch, make representative drawings of the parapodia in at least two of the species. How do these parapodia differ? How are they similar? Can you tell where the species live based on the kind(s) of parapodia?

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   Some Pertinent Books Found in Lamson Library:
   1. Hess, Helen C. 1993. The American Naturalist. v141. New York, NY: Expanded Academic Index. li>Lindsay, Sara M. and Sarah A. Woodwin, 1992. The Biological Bulletin. v183. New York, NY: Expanded academic Index.
   2. Thistle, David, Brigitte Hilbig and James E. Eckman. 1993. Deep-Sea Research. Part I, Oceanographic Research Papers. v40.

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      (James P. DelPrete, Fall 1994; Edited by Betty Miller, Spring 1995)