A Field Guide to the Snails of Lord Howe Island

84 Family Helicarionidae (Glass snails and semislugs) The Helicarionidae is a group of snails and semislugs with its greatest diversity in eastern Australia, where there are over 100 species. The family is also found on Pacific islands, throughout southeast Asia, parts of Africa, and Madagascar and the Mascarene Islands. Around half of the species are snails and half are semislugs, with reduced, ear-shaped shells into which they cannot fully retract their bodies. Evidence suggests that shell reduction has evolved independently multiple times in this group. Australian Helicarionids have shells of 5-38mm in diameter, with the Lord Howe Island species numbering among the largest known. Both snails and semislugs usually have thin, glossy shells with minimal sculpture, usually of fine incised grooves on both protoconch and teleoconch. Shell shape ranges from globose to discoidal to ear-shaped to plate-like, with a whorl profile ranging from rounded to keeled. The outer lip is thin and the umbilicus is closed or very narrowly open. Shells are usually transparent golden or amber, often with a greenish or reddish tinge and occasionally with a spiral band. Most species have pronounced mantle lobes (which lie over the body) and shell lappets (which lie over the shell), which are narrow and finger-shaped in some snails and greatly expanded in others. It is common for the shell lappets to completely cover the shell when the animal is resting, and in some semislug species, the shell lappets are partially fused, leaving only a small window through which the shell can be seen. Helicarionids have a pronounced caudal horn on the end of the tail and a tripartite sole. Nitor pudibundus , an eastern Australian snail belonging to the genus that gave rise to the Lord Howe Island helicarionid radiation.