RISSOINIDAE STIMPSON, 1865

FAMILY RISSOINIDAE STIMPSON, 1865 View in CoL

Treated as a subfamily of Rissoidae by Ponder (1985a), this group was previously treated either as a separate family (e.g. Laseron, 1956; Coan, 1964) or considered a junior synonym of the Rissoidae (e.g. Wenz, 1938 – 1944). In our analysis, it contains five species representing three genera. Rissoinids are characterized by two distinct autapomorphies: an anterior notch in the inner lip that forms a small channel without an embayment or excavation ( Fig. 3A View Figure 3 ), and a long curved opercular peg ( Fig. 3D View Figure 3 ). In particular, the opercular peg differs from that of the sister group Barleeidae in having a spiral inner end and the operculum is paucispiral and yellow, not concentric and red as in the latter group. Rissoinids and barleeiids differ by a number of additional characters which are described above. The Rissoinidae differ from the Zebinidae in having a strongly pegged, thick yellowish operculum and a differently formed anterior channel (as described above) or this latter structure is absent in Zebinidae . The posterior chamber of the stomach is very long ( Ponder, 1965, 1985a) (Supporting Information, Fig. S1C) and at least some rissoinids feed on forams ( Ponder, 1965).