Published online by Cambridge University Press: 11 May 2009
The sipunculanPhascolion strombi (Montagu) is well known for its habit of sheltering in empty mollusc shells. In European waters, a variety of animals are to be found associated with this sipunculan in its shelter (see Kristensen, 1970), including the pyramidellid gastropodMenestho diaphana (Jeffreys) and the erycinacean bivalveMontacuta {Tellimya) phascolionis Dautzenberg & Fischer. Neither of these two species has been recorded as living in association withP. strombi in British waters but a recent examination ofP. strombi-inhabited shells in the vicinity of Plymouth has shown both to be present in the area.
Like all pyramidellids, M. diaphana is an ectoparasite although for many years after its description by Jeffreys (1848, as Odostomia) from Exmouth, Devon, its host animal(s) remained unknown. It was first discovered associated with P. strombi by Perez (1924, 1925) at Roscoff, Brittany, and subsequently described by Dautzenberg & Fischer (1925) under the name Odontostomia (Auristomia) perezi. The possibility ofO. perezi being synonymous with the speciesdiaphana, placed in the genus Menestho by Fretter & Graham (1962), was first suggested by Thorson (Thorson, in Robertson & Orr, 1961), a view supported by Ockelmann (Ockelmann, in Ankel & Christensen, 1963) and Kristensen (1970). Recently, Rodriguez-Babio & Thiriot-Quievreux (1974) demonstrated that the protoconchs of the' free-living' individuals (M.diaphana-type) are similar to those of individuals living withP. strombi (O.perezi-xype). In shell shape, specimens associated withP. strombi at Plymouth closely resemble the holotype ofO. diaphana, now in the collections of the Smithsonian Institution (V. Fretter, personal communication). Thus & Fischer named O. perezi without reference to it would appear that Dautzenberg O. diaphana material, or perhaps were impressed sufficiently by its regular association strombi as to regard it as a distinct species. In either case, it seems to have been now established that perezi is a synonym of diophana.