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 smaller than H. gemma gemma (up to about 2.3 mm in length compared with 2.5 mm), is yellowish-white (not orange-brown) and the suture is strongly canaliculate (weakly to not canaliculate in H. gemma gemma).
The penis is simple in all Hemistomia species.
Hemistomia gemma suturalis Ponder, 1982
Class Gastropoda
Infraclass Caenogastropoda
Order Littorinida
Suborder Rissoidina
Superfamily Truncatelloidea
Family Tateidae
Genus Hemistomia Crosse, 1872
Original name: Hemistomia gemma suturalis 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: Southern tributary of Rocky Point stream, just above connection with main creek a little behind coastal cliff, 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.
Streams on eastern slopes of Smoking Tree Ridge, northern slopes of Mt Lidgebird and Big Slope on eastern side of Mt Gower, Lord Howe Island.
All the Hemistomia species are strongly clustered into distinct geographical locations on 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.
