Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Mollusca
Class Gastropoda
Clade Sorbeoconcha
Superfamily Cerithioidea
Common name: freshwater snails
Overview
Cerithioidea are aquatic snails that mostly occur in marine habitats, with a few groups found in brackish and freshwater. They have coiled, elongate shells that may be smooth or sculptured, sometimes strongly, and often patterned. The head possesses a pair of eyes near the base of a pair of non-invaginable, but retractable cephalic (head) tentacles. Respiration occurs via a single ctenidium (gill) and they typically have a horny operculum.
Distribution and diversity
Three freshwater Cerithioidea families occur in Australasia: Thiaridae, Pachychilidae and Melanopsidae. Thiards are distributed worldwide, occurring in temperate, subtropical and tropical regions and includes some widely dispersed tramp species. The Australian thiarid fauna comprises around nine described species in five genera that are found across northern and eastern Australia, including the large inland drainage basins, extending into South Australia. The 12 described genera of Pachychilidae have a Gondwanan distribution with representatives in South and Central America, Africa, Madagascar and Southeast Asia with one genus with two species in Australia from the Torres Strait Islands. The Melanopsidae mostly occur in Europe and Africa but one genus is found in New Zealand and New Caledonia.
Life cycle
Many Cerithioidea typically reproduce parthenogenetically though some also sexually. Populations reproducing sexually have separate sexes. Very high variability between populations can occur in species that reproduce by parthenogenesis. They may be viviparous or oviviparous. Young are typically retained in a brood pouch where they develop. Young are usually released as small snails.
Feeding
Cerithioidea are herbivorous, detritivorous or omnivorous grazers, feeding on algae and detritus by scraping their radula (teeth) along the substrate as well as scavenging from the carcases of dead animals.
Ecology
The ability of Cerithioidea, particularly many Thiaridae, to reproduce very rapidly through parthenogesis enables them to rapidly colonise new environments. Thiards are also often found in large numbers and are important components of the diets of fish, birds or mammals. In muddy habitats in coastal Queensland streams they are often the dominant molluscs. Thiards are of biological and economic importance as intermediate hosts for a variety of tremode parasites of fish, domesticate animals and humans (lung fluke). Some species of Thiaridae used in the aquarium trade have become invasive in certain parts of the world.
