A Field Guide to the Snails of Lord Howe Island

142 Family Valloniidae (Grass Snails) Introduced: Subfamily Valloniinae Vallonia excentrica Sterki, 1893 Shell. Size: H = 1.1 mm, D = 2.2-2.3 mm. Colour: White, shining. Shape: Discoidal with a low spire; whorls rounded; last whorl expanding; sutures impressed. Sculpture: Protoconch with fine spiral cords; teleoconch with fine, closely spaced, irregular radial ribs. Aperture: Circular; lip thickened and flared. Umbilicus: Widely open. Animal. Body white; optic tentacles short, club-like. Key distinguishing features. Minute size; white shell and body colouration; discoidal shape; flared last whorl and thickened lip; open umbilicus. Habitat and occurrence. Vallonina excentrica is a species with a Holarctic distribution which is now invasive worldwide. It has been introduced into southeastern Australia, including Lord Howe Island and Norfolk Island. On Lord Howe Island, where this species was first recorded in 1999, it is most common in the settlement area, but is also known from the North Bay area, the Intermediate Hill area, and the slopes of the southern mountains. It is found in leaf litter and under logs, in both disturbed and undisturbed habitats. Remarks. Similar in shape to some native charopids and punctids, but differs in its thickened and flared lip and in its white shell and body colouration with fine, irregular ribs. Vallonia excentrica 1 mm