A Field Guide to the Snails of Lord Howe Island

135 Pernastela gnoma Iredale, 1944 Dwarf Pinhead Snail Shell. Size: H = 0.8 mm, D = 1.2-1.3 mm. Colour: Golden brown. Shape: Trochoidal with a moderate spire; sutures impressed; whorls shouldered. Sculpture: Protoconch with spiral lirae; teleoconch with widely spaced radial ribs and distinct spiral microsculpture. Aperture: Ovately lunate. Umbilicus: Narrow. Animal. Not known. Key distinguishing features. Minute size, distinct radial ribs and microspirals on teleoconch, shouldered whorls. Habitat and occurrence. Common and widespread across the whole island. Living in litter. Remarks. Differs from P. charon and P. howensis in its much smaller size and shouldered whorls. Pernastela howensis Iredale, 1944 Lord Howe Pinhead Snail Shell. Size: H = 1.8-2.1 mm, D = 3-3.3 mm. Colour: Pale golden brown to cream. Shape: Trochoidal with a raised spire; whorls rounded above and flattened below an angulate periphery. Sculpture: Protoconch with spiral lirae; teleoconch with strong, sinuate, closely spaced radial ribs; microsculpture of spiral lirae. Aperture: Roundly lunate, flattened on upper side by reflected lip. Umbilicus: Moderately wide. Animal. Not known. Key distinguishing features. Very similar to P. charon, differing only in its more closely spaced ribs. Habitat and occurrence. Known only from the type material, three worn shells collected from the Mt Gower summit in 1912. Remarks. This species could be considered to be a synonym of P. charon , as the only discernible difference is in the spacing of the ribs. However, Pernastela charon has never been collected from Mt Gower, and it is possible that P. howensis is a rare or even extinct form endemic to the southern mountains. Dedicated leaf litter collecting may allow this elusive species to be rediscovered.