By Jean Anselmi
There are animals that are so different from us, we struggle to consider them animals. But this month’s feature animal has been around 550 million years, has thousands of species, comes in a huge variety of shapes and sizes, and copes with a wide diversity of environments.
I suppose the pictures gave it away, but would you have guessed the animals were sponges?
Sponges are members of the phylum Porifera, and although they are very simple organisms, they belong in one of the most diverse phyla on earth. There are nine thousand identified species of sponges, varying from microscopic to the size of your car, with a wide array of shapes and colours.
Sponges don’t have a proper mouth or digestive system (or any proper organs). They also don’t have a nervous system or muscles and most generally attach to one place and stay there (although studies have suggested some species can crawl slowly).
Mid writing this article, I asked my sister “Do you have any interesting sponge facts?” She said “They don’t have bones and must be related to jelly.” Only one of these is relatively true, because although they do not have bones like ours, sponges do have a skeletal structure.
Using much more scientific methods than my sister, Aristotle classified sponges as plants, which seems a reasonable conclusion. However, sponges are animals because, among other reasons, they lack cell walls, are multicellular, reproduce using sperm cells, and have a skeletal structure.
Although they are found in virtually all aquatic habitats, most sponges are marine species, suggesting there are probably many species still to be discovered. The fantastic Jawbone Marine Sanctuary located off the coast of Williamstown in the traditional Sea Country of the Bunurong People is home to several species, photographed and classified by the Jawbone Marine Sanctuary Care Group (JMSCG). (It might be important to state that none of the knowledgeable people of the JMSCG were consulted in this very unscientific column.)
Some sponges contain toxic substances to discourage predators. These sponges are particularly attractive to specific species of crabs that wear sponges as camouflage and to take advantage of the sponge’s toxic deterrent. The crabs cut a section of a sponge, holding it on their head with specialised hind legs, where the sponge continues to live and grow. Recently, a new species of crab was found in Western Australia with dense, shaggy hair and wearing a sponge hat. Very fashion forward.
With all these varieties, there is one shape you can’t find. At the risk of body shaming, sorry SpongeBob SquarePants, but square is not a realistic portrayal.
https://www.parks.vic.gov.au/places-to-see/parks/jawbone-marine-sanctuary
