Peanut Worms — Phylum Sipunculida

Sipunculids (siphunculus = "little tube") are commonly known as peanut worms because of their resemblance to shelled peanuts. Only three species are found in the Canadian Arctic: Golfingia margaritacea, G. hudsoniana, and Phascolion strombus. Peanut worms use specialized muscles to burrow into the sand and mud, but they also inhabit rock crevices or empty shells. Most sipunculids are less than 10 cm long, but a few reach lengths up to 72 cm!

Peanut worms resemble annelids, but show no evidence of segmentation. Their body is sausage-shaped and is divided into two regions: a retractable structure, called the introvert, and the trunk. The front end of the introvert bears the mouth, which is surrounded by a ring of feeding tentacles. These tentacles are covered with mucous and can be used to either feed on organic detritus located on the substrate or to consume plankton via filter feeding.

Sipunculids are capable of regenerating lost parts of their tentacles, introvert, trunk, or internal digestive system. Some species are able to "clone" themselves by breaking into a large front portion and a smaller back portion, each capable of regrowing their missing parts, and resulting in two separate organisms. To reproduce, sipunculids release their sex cells into the surrounding water to produce free-swimming juveniles.