A Field Guide to the Snails of Lord Howe Island

8 genera of semislugs and no true slugs. However, there are three introduced slug species. The most obvious feature of most species is the shell . All shell features described below are are illustrated on the inside back cover. Shells are spirally coiled, with the coils referred to as whorls . Some species have determinant growth, and at maturity new whorls will no longer be added, but instead the shell may become thickened. Other species with indeterminant growth will continue to add new whorls even after maturity is reached. Semislugs, with their reduced shells, have a lower adult whorl count than snails. The direction of coiling of a shell can be dextral (right- handed or clockwise) or sinistral (left-handed or anti-clockwise). Whorls can be coiled tightly or loosely, and can expand rapidly or slowly. Shell shape can be discoidal, conical, trochoidal, turbinate, globose, pupiform, ear-shaped, or plate-like. If the shell is intermediate between shapes, the closest descriptor may be used, with the prefix ‘sub’ (e.g. subglobose for a shell that is more flattened than a truly globose shell). A combination of descriptors is often used (e.g. globosely turbinate; discoidal with a low, conical spire). When the shell is viewed from the side, the outer edge ( shell periphery ) can be rounded, angulate, or keeled, and the whorl profile can be rounded, flattened, shouldered, or sulcate (i.e. with a supraperipheral sulcus) above the periphery, and rounded or flattened below it. The spire or apex of a shell can be sunken, flat, low, moderately to strongly raised, elongate, or stepped. The sutures , which are the lines along which adjoining whorls meet, can be smooth (not impressed), weakly to strongly impressed, or channelled (forming a channel). The opening of the shell is called the aperture . The shape of the aperture can be lunate, ovate, subovate, rounded, teardrop-shaped, angulate, or some combination of these (e.g. ovately lunate). Some species have apertural teeth. The outer edge of the aperture, or lip , can be simple, thickened or reflected. The columella , which is the central axis of the shell, is primarily contained inside the shell and can only be seen at the inner edge of the aperture. It can be straight or twisting, simple or thickened, and can bear teeth. On the underside of the shell, the umbilicus can be closed, or narrowly, moderately or widely open. If the umbilicus is open, the opening can be straight-sided (like a cup) or can have inclined sides (like a bowl).