bristleworm coloration

[kfisc]

Among the bristleworms in my tank (all of whom are perfectly innocent of any crimes against tridacnas!) is a fairly large specimen of the common orange/bristle-laden variety, roughly 5" or so long without stretching, just moving about at night. I notice the larger these folks get, the more striking their color- as if light is being reflected off a mucous covering, perhaps similar to what common earthworms display, reflecting rainbow colors in sunshine when wet. Is there a mucous covering that causes the "shimmering" color effect on bristleworms when in direct light? Also, the body coloration of the worms is fascinating/beautiful in its own right- any ideas about evolutionary benefits in color development? Is it related to the fact that poisonous creatures are often brightly colored? Thanks a lot-

[rshimek]

Hi,

The iridescence is caused by their cuticle. It is a thin proteinaceous layer on the outside of the body, and the various ways that light reflects/refracts off and through it cause the colors. There has been little work on the color of these animals, but some of them (such as the fireworms) obviously have aposematic or "warning" coloration. Others... ???

Ther are many marine biologists that consider some of the worms to be the most beautifully colored of all marine animals.