Sponges

Code IA999999

Key terminates here

Family Spongillidae

Code IA019999

Sponges are sessile organisms with no bilateral symmetry, no clear anterior/posterior axis, limited differentiation of tissues into organs and no nervous system. Most are marine but they occur also in semi-permanent and permanent, running and still, fresh and brackish water. Sponges feed via choanocyte (collared) cells which line internal water-filled cavities. The internal canal system opens through numerous small incurrent pores and fewer but larger excurrent pores scattered over the body surface. The body is covered by a simple epithelium of flattened cells without a basement membrane.

Freshwater sponges vary in colour from pale cream to green. Growth is variable within species. Specimens from still water often consist of several irregular lobes. In running water the tendency is toward a mat-like structure. Sponge reproduction is by gemmules, and gemmule characters are much used in identification at genus and species level.

Geographical distribution is much affected by chemical characteristics of the water, with acidity or alkalinity a major factor in determining where a given species will occur. Climatic factors also have some influence. The sponges of western and inland Australian waters are relatively firm and in some cases almost stony-hard. Those of the less climatically harsh but generally acidic eastern drainages often are softer and more typically sponge-like to the touch.

All freshwater sponges are placed in class Desmospongia, family Spongillidae. This family is almost certainly paraphyletic (Racek, 1969). Twenty-six Australian species have been described (Hooper and Wiedenmayer, 1994), of which twelve are endemic. According to Racek (1969), it is likely most species occur naturally. Only Spongilla alba , which is restricted to tidal reaches of the Brisbane River, can be regarded as most probably introduced.

Racek (1969) gives a key to genera, and Hooper and Wiedenmayer (1994) catalogue the Australian species.

Identification

For the softer species, identification as a sponge, hence Spongillidae, can be based on the sponge-like, resilient feel. For stony species, it is sufficient to note the presence of numerous small incurrent pores and less numerous but larger excurrent pores. Internally, all species possess a skeleton of siliceous spicules and spongin fibres, and the internal cavities are lined with collared, flagellated cells (choanocytes). Spicules can be recovered by taking a small portion of sponge and dissolving the soft tissues in dilute KOH. Spicule shape is of importance in generic and species level identification.

References:

Hooper, J.N.A. and Wiedenmayer, F. (1994) Porifera. In: Wells, A. (ed.) Zoological Catalogue of Australia . Volume 12. AGPS Press, Canberra.

Racek, A.A. (1969) The freshwater sponges of Australia (Porifera: Spongillidae). Australian Journal of Marine and Freshwater Research 20 : 267-310.