Sipunculans

Peanut Worms

Photographs of sipunculans donated by Jeanne Smith.  Generally all that is seen of the animal is the introvert which may extend out of holes or crevices in the rocks.

Photographs of sipunculans donated by Collin Gayde.

These are small to moderately large worms that live in rocks or crevices.  They are harmless sediment or detritus feeders.  These odd worms are common on reefs and have shown up frequently in live rock imported over the last few years.  The major distinguishing characteristics are the lack of segmentation, and the way in which the introvert extends or retracts by unrolling from within itself or pulling back within itself respectively.

Peanut worms are frequently found in newly acquired live rock and are actually very common on reefs themselves. Nevertheless the aquarist will seldom see the whole animal. They live buried deep in the rocks in burrows that they erode by the use of chemicals and rasping regions on their body.

They are long, rather urn shaped worms that lack a head or segments. Really, they do look like smooth peanuts (in the shell) with a long tapered front end. The body, on some, can be about the size of a peanut, but most are a lot smaller. The long tapered end typically bears a cluster of small mop-like tentacles and the mouth is in between their bases. When the animal feeds, it contracts its body and the internal fluid pressure forces the long tapered end, called an " introvert" to expand. It unrolls from the inside out, rather like pushing out the finger of a glove that has been pushed into body of the glove. It will expand outward and then start to daub the bottom, collecting debris and particulate material which is eaten.

When the animal is startled or finished eating, it relaxes its body muscles and powerful retractor muscles contract introverting the introvert and retracting it.

What most hobbyists see is what appears to be a worm-like structure, often described as a miniature elephant's trunk extending outward from the rock touching the bottom. The outside of this structure, obviously the extroverting introvert, is often banded or mottled gray, green, brown, or black.

These animals will do well at reef normal conditions and may thrive, but generally their aquarium population will slowly dwindle as they suffer occasional mortality from hermit crabs, or fish. They are harmless and interesting, if transitory, inhabitants of our systems.

 

Interesting or Useful References:

Gibbs, P. E. and E. B. Cutler. 1987. A classification of the Phylum Sipuncula. Bulletin of the British Museum of Natural History (Zoology). 52:43-58.

Kohn, A. J. and M. E. Rice. 1971. Biology of Sipuncula and Echiura . Bioscience. 21:583-584.

Rice, M. E. 1993. Sipuncula. In : Harrison, F. W. and M. E. Rice. Eds. Onychophora, Chilopoda, and Lesser Protostomes. Wiley-Liss. New York. pp. 237-325.