The genus Liotipoma McLean & Kiel, 2007, was proposed for a remarkable small-shelled gastropod genus from coral reefs of the Indo-Pacific that resemble the family Liotiidae Gray, 1850 in having fine axial lamellae and a thickened terminal lip, but differ in having the solid calcareous operculum of the family Colloniidae Cossmann, 1916. The genus was originally assigned to the otherwise Cretaceous subfamily Petropomatinae Cox, 1960 of the family Colloniidae, because the inner side of the operculum is multispiral, conical and projecting, as in the Mesozoic genera assigned to Petropomatinae. Here the genus Liotipoma is assigned to a new colloniid subfamily Liotipomatinae n. subfam., because its axial lamellae are unknown in the Cretaceous genera of Petropomatinae. Four genera are now recognised; all species are known from shell grit samples collected by diving or dredging at coral reefs from recent MNHN expeditions to New Caledonia, the Loyalty Islands, Espiritu Santo (Vanuatu) and Wallis Island, and also from LACM material from Fiji, Papua New Guinea, and the Marshall Islands. The most speciose genus is Liotipoma, with eight known species, seven of which are new and described here the largest known species is L. magna n. sp. from Santo, Vanuatu. Also described are: Depressipoma n. gen. with two new species from the Marshall Islands; Rhombipoma n. gen., with one new species from Rowley Shoals, northwestern Australia; and Paraliotipoma n. gen., with one new species from Sea Horse Shoal, South China Sea. Although live-collected specimens are still unknown, sexual dimorphism in Liotipoma was reported for the type species when the genus was described. Here it is reported from four of the eight known species of that genus, expressed in expansion of the umbilical cavity as a brood chamber in the female shell, as previously reported in the families Liotiidae and Colloniidae. In two species the worn female shell shows an irregular degradation of the umbilical cavity, which is considered the effect of bearing a large egg mass and brood. For reasons unknown, female shells of most species of Liotipoma are much less frequent than male shells. Formal validation of Areneidae n. fam. is provided in an addendum to this paper.
Gastropoda, Colloniidae, Areneidae n. fam., Liotipomatinae n. subfam., sexual dimorphism, Indo-Pacific, coral reefs, new subfamily, new genera, new species.