Family PHASCOLOSOMATIDAE

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Introduction

After Edmonds (2000)
Members of the Phascolosomatidae are small to medium sized, with the trunk 10-60 mm in length. The body shape varies from bottle-, flask- and spindle-like, to fusiform, to sometimes subcylindricalor, if much contracted, almost rounded. Fewer than 30 finger-like tentacles lie in a near circle dorsal to the mouth and surround the nuchal organ. This latter character is difficult to determine if the introvert is retracted, however, the anterior region of the organ may be dissected. The longitudinal musculature of the trunk wall is grouped into bands which may anastomose; the bands are not always visible externally, but are always revealed on dissection. The introvert and trunk usually bear numerous, pigmented, conical to hemispherical papillae consisting of small plates or platelet; these are most numerous and largest on the anterior and posterior regions of the trunk. Four retractor muscles are present. The contractile vessel is single and lacks villi except in Antillesoma species. Phascolosomatids are distinguished from aspidosiphonids by the absence of a hard, horny or calcareous anal plate or shield. The type genus is Phascolosoma Leuckart, 1828.

In living specimens, the introvert is capable of considerable extension, but in fixed material it may be half to one and a half times the trunk length. The introvert is usually armed with numerous, closely packed rings of hooks, which often have a characteristic shape and internal marking. The hooks of some species are thought to assist in scraping algae from rocks. The identification of species depends on the shape and markings on the hooks and the size, shape and structure of body papillae. The spindle muscle is fastened posteriorly near the extremity of the trunk.

The family, according to Gibbs & Cutler (1987), comprises three genera: Phascolosoma, Apionsoma and Antillesoma. The first of these is a very large genus and the other two very small. Phascolosoma species are the most commonly collected intertidal sipunculans in Australia. They live in burrows in limestone and coral reefs, in encrusting masses of tubicolous polychaetes (such as Galeolaria species), in clumps of mussels, in rock crevices, under stones and in mangrove flats. Most appear to be detritus feeders. Phascolosomatids are common, especially in the warm shallow tropical and temperate waters of the world. The species that occur in Australian waters are also well known in the western Pacific and regions of the Indian Ocean. Edmonds (1980) recorded 11 species from Australian waters. Golfingia misakiana and G. trichocephala listed by Edmonds (1980) were transferred to Apionsoma by Gibbs & Cutler (1987).

The shape of members of this family when contracted is probably responsible for the common name "peanut worm", as they then resemble peanuts in size and shape, and are light brown in colour.

General References

Cutler, E.B. 1994. The Sipuncula, their Systematics, Biology, and Evolution. New York : Cornell University Press 480 pp.

Edmonds, S.J. 1980. A review of the systematics of Australian sipunculans (Sipuncula). Records of the South Australian Museum (Adelaide) 18: 1-74

Edmonds, S.J. 2000. Phylum Sipuncula. pp. 375-400 in Beesley, P.L., Ross, G.J.B. & Glasby, C.J. (eds). Polychaetes & Allies: The Southern Synthesis. Fauna of Australia Vol. 4A Polychaeta, Myzostomida, Pogonophora, Echiura, Sipuncula. Melbourne : CSIRO Publishing Vol. 4 Part A xii 1-465 pp.

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

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