The Sipuncula, sipunculid worms or peanut worms, are a phylum containing 144-320 species (estimates vary) of bilaterally symmetrical, unsegmented marine worms. Sipunculid worm jelly (土笋冻) is a delicacy in the town of Xiamen in Fujian province of China.
Habitat
Sipunculids are relatively common, and live in shallow waters, either in
burrows or in discarded
shells like
hermit crabs do. Some bore into solid rocks to make a shelter for themselves. Although typically less than 10
cm long, some sipunculans may reach several times that length.
Anatomy
The most reconisible part of sipunculan worms is their mouth, which is surrounded by a mass of
tentacles, all of which may be inverted into the body. The
digestive tract of sipunculans passes from the mouth to the posterior end of the body, before twisting back around itself and ending at the
anus, on the side of the body. A few taxa possess a calcified plate called the anal shield. Sipunculans have a
coelom. However, they do not have a vascular blood system. Instead, interstitial fluid transports
oxygen and
nutrients around the body. A separate cavity fills the hollow tentacles; it passes oxygen from the tentacles to the coelom. The body wall is strong and
muscular; when threatened, sipunculids can retract their body into a shape resembling a
peanut kernel. This is where the name "Australian peanut worm" comes from.
More on
[ Sipuncula ]
Ed Cutler's Sipuncula Research - Includes detailed classification of the 144 species in Phylum Sipuncula.
Introduction to the Sipuncula - Introduction to the peanut worms, from UCMP Berkeley.