A Sipuncula, peanut worm worms or even peanut worms, come the phylum containing 144-320 species (estimates vary) of bilaterally symmetrical, unsegmented marine worms. Peanut worm worm jelly (土笋冻) occurs as delicacy in the town of Xiamen in Fujian province of China.

Habitat
Peanut worm come comparatively most common, & sleep inside shallow waters, either in burrows or inside thrown-away shells like hermit crabs do. the select few wore into firm rocks to produce a shelter for themselves. Although generally less than Decade cm long, some sipunculans will email many days that length.

Anatomy
the virtually all noticeable feature of sipunculan worms is their mouth, which is surrounded by a ring of tentacles, all of which can be inverted into a system. A digestive tract of sipunculans passes from either a mouth to a tail prevent of the person, prior to twisting back around itself & ending at the anus, on the side of the system. Two or three taxa possess a calcified shell known as the anal shield. Sipunculans come coelomate, meaning they possess a fluid-filled cavity within a immune system, & this fluid (the celoma) transports oxygen and nutrients around a system. a separate coelomic cavity fills a hollow tentacles, & lives atomic number 8 from either the tentacles to the trunk celom. A immune system wall is hard & muscular; when threatened, insignificant worm might retract their system into the shape resembling the peanut kernel. This is in which a title "peanut worm" comes from either.

Relationships
A phylogenetic placement of this phylum has proved troublesome. Originally classified when annelids, despite the complete want of segmentation, bristles and other annelidan characters, a phylum Sipuncula was late allied sustaining a Mollusca, mostly from developmental and larval characters. Today, these ii phyla come usually involved inside a big class action, the Lophotrochozoa, that also includes annelids, ribbon worms, and quaternity more phyla.

Fossil record
A fossil record of the Sipuncula is, non amazingly for soft-bodied beast, thin. A bit of man of science, nevertheless, assume that hyoliths, operculate shells from a Palaeozoic may be related to a sipunculids, by owning a lone remnant of the casing inside extant forms existence the anal shell.