Family Squamapicidae Zhang and von Rintelen fam. nov.

LSID urn:lsid:zoobank.org:act: 376F3C07-B91D-4855-9337- 283099B0D1E2.

Type genus: Squamapex Zhang and von Rintelen gen. nov..

Diagnosis: Shell minute, number of whorls around three; twostage protoconch, first half of protoconch whorl with weak sparse veins, the remainder of the protoconch whorl strongly ornamented, covered with many lines of regularly distributed large, square-scale-shaped pits, teleoconch without complex microsculpture; operculum kidney-shaped, inner opercular region hourglass-shaped, with two different projections on the upper and lower part of the inner opercular region; central teeth of radula trident-head-shaped, with three sharp triangle cusps and a pair of long basal denticles.

Taxonomic remarks: Squamapicidae are a monotypic family of Truncatelloidea, containing the monotypic genus Squamapex gen. nov. with the single species Squamapex taiji gen. et sp. nov .. Characters of the radula and head–foot, support that Squamapicidae belongs to Truncatelloidea. However, this family is distinct from any other known family within Truncatelloidea due to its highly sculptured protoconch with many rows of scaleshaped depressed pits and operculum with two projections on the hourglass-shaped inner opercular region. The species of Kobeltocochlea Lindholm, 1909 of the family Lithoglyphidae Tryon, 1866, endemic to Lake Baikal, have a strongly reticulate embryonic shell and smooth teleoconch. However, Squamapex taiji gen. et sp. nov. can be easily differentiated from the species of Kobeltocochlea based on the shell morphology, operculum and radular structure.

Distribution: This family currently is only known from one ancient freshwater lake: Fuxian Lake, in Yunnan, China.