Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Porifera, Class Demospongia
Order Haplosclerida, Suborder Spongillina

Common name: sponges

Overview

The phylum Porifera contains predominantly marine sponges; it is only in the suborder Spongillina within the order Haplosclerida that the freshwater species are found. Freshwater sponges show a high diversity of colours, sizes, body shapes and textures and are found worldwide. The key character that is thought to have enabled the diversification of sponges into inland waters is the presence of gremmules. Gremmules are internal buds which form through asexual reproduction and are resistant to harsh conditions, allowing the sponge to resist hostile environments in a resting phase and re-establish when conditions are more suitable. The oldest fossil evidence of freshwater sponges is from the Cretaceous.

Distribution and diversity

The freshwater sponges have colonised a wide range of environments and substrates at all latitudes. There are approximately 220 species of freshwater sponge from 45 genera in six families worldwide. Two families (Spongillidae and Metaniidae) consisting of 11 genera and 27 species are reported from Australia.

Life cycle

A generalised life cycle of a freshwater sponge can consist of five stages that can be repeated several times a year. A vegetative growth phase is followed by gemmulation (asexual reproduction) or sexual reproduction, cryptobiosis (resting phase), the hatching of gemmules, and finally regeneration. If sexual reproduction is occurring, parenchymella larvae are produced and disperse before developing into the mature sponge. Most Australian species are thought to reproduce by asexual reproduction.

Feeding

Sponges feed by filtering bacteria and organic particles out of the water. Water-conducting canals throughout their tissue allow the water to flow through chambers where food particles are caught by flagellated cells (choanocytes) which are similar in operation to a kitchen strainer.

Ecology

Freshwater sponges can be found in a surprising range of depths and have been known to survive huge variations in chemical and physical conditions. They are found encrusting onto surfaces beneath the water. Substrates can include everything from rocks to roots and branches to man-made structures.

Ephydatia fluviatilis
Image credit: Malcolm Storey, 2010, BioImages - the Virtual Fieldguide (UK)
used under a Creative Commons Attribution-NonCommerical-ShareAlike license

Spongilla lacustris, a cosmopolitan species of freshwater sponge
Image credit: Kirt L. Onthank
used under a Creative Commons Attribution-ShareAlike license