Marsh snails, black snails
Class Gastropoda: Subclass Prosobranchia: Order Monotocardia.
A world-wide distributed family of almost exclusively freshwater snails. The family includes some widely-dispersed tramp species, and is known from many temperate to tropical islands. Many, but not all, species reproduce by parthenogenesis, giving rise to very high variability between populations.
Thiarids are characterised by a medium to large, elongate, high-spired shell, often with nodules and a horny operculum.
The Australian fauna comprises at least en widespread species in seven genera. Distribution ranges from Eastern and Northern Australia including the large inland drainage basins, extending into South Australia. Often found in great numbers, and in coastal Queensland streams, where they are regularly the dominant molluscs, often in muddy habitats.
Smith, B.J. (1996) Identification keys to the Families and Genera of Bivalve and Gastropod Molluscs found in Australian Inland Waters . Cooperative Research Centre for Freshwater Ecology Identification Guide No. 6., Albury, NSW.