A Field Guide to the Snails of Lord Howe Island

26 Caenogastropoda The Caenogastropda is the largest and most diverse group of gastropods, demonstrating a huge diversity in body and shell form and being found in all major habitats. The majority of species are marine, but some species have invaded freshwater and terrestrial environments. Caenogastropods typically have a coiled shell, but exhibit a wide variety of shell shapes, ranging from limpet-like to depressed to globose to elongate. Some species have the shell reduced to an internal remnant and others have uncoiled shells. Shell size ranges from <1–400 mm, and both shell and body can be brightly coloured, patterned and ornamented. Most adults have an operculum. The head has a single pair of tentacles which bear eyes at their base. Caenogastropods have a pallial cavity containing a gill (or ctenidium) and associated sense organs. Terrestrial species have lost the gill and instead the pallial cavity acts as a lung. The majority of species have separate sexes (although a few are hermaphroditic). There are a wide variety of reproductive and developmental strategies, including direct development (where juvenile snails hatch from the egg) and indirect development (where there is a free-swimming larval stage). Bembicium flavescens , a marine caenogastrpood endemic to Lord Howe Island. Image C. Woods.