polychaete setae

A conspicuous characteristic of most polychaetes are the many setae found on each segment. Here’s a photo of a fireworm, which I promised in class. Their setae are extended further from the body when the worm is disturbed so that an agitated worm is covered along each side with bright white tufts of setae. These setae contain a toxin, and just a slight brush up against them causes them to pierce the skin, break off, and cause a most unpleasant burning sensation. Look, but don’t touch.

Setae are definitely worth a close up look if you get a chance to see them under a compound microscope. The setae are formed during development and throughout the life of the adult worm as they break off during use. As larval polychaetes grow, the setae can be easily seen on each new segment.