The 54 putative species of the nominate sipunculan subgenus Phascolosoma (Phascolosoma) and the morphological characters used to differentiate them are critically reviewed. The monograph of Stephen & Edmonds (1972) is used as a starting place and all changes made in the intervening years are reiterated here. Available type material was studied and new collections of Hawaiian and Caribbean worms are used to analyze within-deme variation. Twenty chromosomes of gradually differing sizes are present. Four characters are broadly useful at the species level (number of hook rings, secondary tooth of hook, pigment on introvert, and pre-anal papillae). Eight characters can be used in a more restricted manner for subsets or special cases (hook size, a.ngle of hook-tip, internal clear areas, basal elaborations, nephridial length, trunk papillae shape, papillae platelets, and retractor origins). Six appear to be of no value to the taxonomist (hook presence, introvert length, number of longitudinal muscle bands, nephridiopore/anus relationship, rectal caecum, and contractile vessel). A key to, and a discussion of, the 16 remaining species (plus two reduced to subspecies) with newly designated synonyms are presented. A brief statement of the distribution of each species is given. An overall summary of the zoogeography and habitat shows the border area between the Indian and Pacific Oceans to be the most diverse with respect to Phascolosoma (81 % of known species). Nineteen percent (three species) live in the Caribbean. With a few exceptions this genus lives in warm, shallow waters and hard substrates.
From the introduction.
This work concludes our reexamination of the sipunculan genera (Cutler & Jurczak 1975; Cutler & Murina 1977; Cutler 1979, 1986; Cutler & Cutler 1982, 1983, 1985a, 1985b, 1986, 1987a, 1988, 1989; Cutler et al. 1983; Gibbs et al. 1983). The monograph of Stephen & Edmonds (1972) is the starting place for this work ( 40 species names). The five species erected and the nine species transferred into this genus since that time are also included (Table 1). The genus Phascolosoma was erected by Leuckart in 1828, placed in the family, Phascolosomatidae by Stephen & Edmonds (1972), and in the order Phascolosomatiformes by Cutler & Gibbs (1985). The general name Phascolosoma went through an unfortunate period when it was incorrectly used to replace Golfingia for seventy years (1880 to 1950). During this time the names Phymosoma and Physcosoma replaced Phascolosoma. In 1950 Fisher reestablished the correct usage of these names
