Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Mollusca
Class Gastropoda
Clade Neritimorpha
Family Hydrocenidae

Common name: minute land snails

Overview

Hydrocenidae are poorly known, tiny terrestrial snails. They have ovate to globose, conical-spired shells and a semi-circular calcareous operculum that possesses a digit-like protrusion on the surface of attachment to the foot. True head tentacles are absent although a pair of broad lateral invaginable appendages may be present, and the pair of large eyes are positioned in papillae. The ctenidium (gill) is absent and the mantle cavity is highly vascularised and functions as a lung. Hydrocenidae are very small snails being less than 10mm in diameter with a shell height of less than 5mm with some species only having a shell height up to 2 mm and width up to 1 mm. Shells are typically dull-coloured and mottled that blend into their habitats well.

Distribution and diversity

Hydrocenidae are a small family of snails that occur from Europe and Africa through Asia to the Pacific region including Australia and New Zealand. In Australia there are only six described species in two genera (Georissa and Monterissa) recorded from New South Wales, Queensland, and Western Australia.

Life cycle

The mating behaviour of Hydrocenidae is poorly known but sexes are separate and fertilisation is internal. Development is direct with juvenile snails hatching from small oval pale or transparent gelatinous eggs that are laid by the female in clusters on the ground in leaf litter or attached to rocks.

Feeding

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

Ecology

In Australia and New Zealand, Hydrocenidae occur on tree trunks, in leaf litter, rotten logs and vine thickets in closed forests. Species are also often found in association with limestone outcrops. On Pacific Islands and in south-east Asia a number of species have been recorded from caves. Several species, such as the endemic Australian species Monterissa gowerensis, are considered threatened, largely due to habitat destruction.