Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Mollusca
Class Gastropoda
Clade Neritimorpha
Family Helicinidae

Common names: land snails, helicinids

Overview

Helicinidae are small to medium-sized terrestrial snails. They have various shell shapes ranging from globose, flattened or conical into which the animal can completely withdraw and a calcareous operculum that unlike that of many other neritopsines, lacks a peg on its inner surface, although sometimes a ridge is present. Some taxa not found in Australia lack an operculum and possess protective ornamentation around the shell aperture in the form of several equally lamellae and or teeth. The ctenidium (gill) is absent and the mantle cavity is highly vascularised and functions as a lung. The head bears a pair of eyes positioned near the base of the pair of invaginable (often short) head tentacles. They typically have brightly coloured, glossy shells with most species showing considerable variation in their colour patterns.

Distribution and diversity

Helicinidae are a tropical and subtropical family of over 500 described species. They are restricted to the Caribbean and some Indo-Pacific and Pacific islands, as well as the margins of the Asian and Australian continents. The family is absent from Europe, Africa, most of Asia, New Zealand, Norfolk and Lord Howe Islands and most of Australia where only 7 species from a single genus (Pleuropoma) have been described.

Life cycle

The mating behaviour of Helicinidae is poorly known but sexes are separate and fertilisation is internal. Females lay eggs in small clusters and development is direct with young hatching as juvenile snails.

Feeding

Helicinidae are herbivorous/detritivous grazers, feeding on detritus, algal spores, moss and lichens by scraping their radula (teeth) along the substrate.

Ecology

Helicinidae are found mainly in tropical rainforest on moist forest floors and the trunks of trees with some species strongly associated with limestone geologies although some species also occur in drier habitats. Australian species are found mainly in tropical rainforest habitats of north-eastern Australia, where some are arboreal in vine thickets and others are associated with leaf litter or limestone outcrops. Helicinids often contribute a significant percentage of the diversity and abundance of the molluscan fauna in tropical forest environments.