The smooth pupiform shell is similar to that of H. pusillior but the operculum is thicker with a curved calcareous patch (not linear as in H. pusillior) and with up to three fused pegs. This subspecies is slightly larger than H. gemma suturalis (up to about 2.5 mm in length compared with 2.3 mm), is orange-brown (not yellowish-white) and weakly canaliculate to simple suture (suture strongly canaliculate in H. gemma suturalis).
The penis is simple in all Hemistomia species.
Hemistomia gemma gemma Ponder, 1982
Class Gastropoda
Infraclass Caenogastropoda
Order Littorinida
Suborder Rissoidina
Superfamily Truncatelloidea
Family Tateidae
Genus Hemistomia Crosse, 1872
Original name: Hemistomia gemma gemma Ponder, 1982. In Ponder, W.F. (1982) Hydrobiidae of Lord Howe Island (Mollusca: Gastropoda: Prosobranchia). Australian Journal of Marine and Freshwater Research 33: 89-159.
Type locality: On south side of east - west ridge to Sugarloaf Point, at head of broad gully in wide seepage along cliff face, Lord Howe Island.
Found in streams, seepages and pools. It is assumed that like most tateids, the Lord Howe Island Tateidae feed on bacteria, microscopic algae, diatoms and possibly decaying vegetation.
Confined to the catchment of the eastern slopes of Mt Gower, Lord Howe Island.
Ponder, W. F. (1982). Hydrobiidae of Lord Howe Island (Mollusca: Gastropoda: Prosobranchia). Australian Journal of Marine and Freshwater Research 33: 89-159.
