Phascolosomatidae, Stephen & Edmonds, 1972

Silva-Morales, Itzahí & Gómez-Vásquez, Julio D., 2021, First records and two new species of sipunculans (Sipuncula) from the Southern Mexican Pacific, European Journal of Taxonomy 740 (1), pp. 77-117 : 105

Family Phascolosomatidae

1. Introvert much longer than twice the trunk length; hooks, if present, with basal spinelets; nephridia usually bilobed ....................................................................................... Apionsoma ........2

– Introvert less than twice trunk length; hooks without basal spinelets; nephridia unilobed ............. ........................................................................................................................... Phascolosoma ........4

2. Body wall muscles divided into separate bands ................................................................................. ................................................................... Apionsoma (Edmonsius) pectinatum ( Keferstein, 1867)

– Body wall with continuous muscle layers ........................................ Apionsoma (Apionsoma) ........3

3. Papillae, hooks and tentacles absent ........... Apionsoma (Apionsoma) trichocephalus Sluiter, 1902

– Papillae, hooks and tentacles present, 7–8 basal spinelets ................................................................ .................................................. Apionsoma (Apionsoma) hespera ( Chamberlin, 1920) comb. nov.

4. Protuberance of the hook streak less than twice the width of the hook .............................................. ................................... Phascolosoma (Phascolosoma) puntarenae Grube & Örsted in Grube, 1858

– Hook without protuberance of the hook streak...............................................................................5

5. Hook triangle indistinct or absent; preanal papillae not distinct from dome-shaped trunk papillae ............................................................... Phascolosoma (Phascolosoma) agassizii Keferstein, 1866

– Hook triangle well-defined; preanal papillae distinct......................................................................6

6. Preanal papillae dome- to mammiform-shaped at the base of the introvert ....................................... ................................ Phascolosoma (Phascolosoma) scolops (Selenka & de Man in Selenka, 1883)

– Preanal papillae conical, posteriorly directed on the dorsal base of the introvert ......................... ..................................................................... Phascolosoma (Phascolosoma) perlucens Baird, 1868