Philippe in Patagonia - page 2
Talking about sponges can lead to confusion. Are they plants or animals? And how do they differ from the sponges used in our own bathtub?
Sponges are aquatic animals living mainly in the sea. The larvae attach themselves to a substrate, where they will stay all their life. Sponges are simple animals, composed of two cell layers. They don't have mouths and lack digestive and nervous systems. They have a unique way of feeding: some cells using whip-like flagella, draw water through tiny pores in the sponges outer membrane. All the usable food is filtered from the water as it passes through the sponge, before it leaves the body through larger openings.
The skeleton is situated between the two cell layers that cover the inner and outer sides of the sponge. This skeleton is obviously very important for its owner's strength, but also for scientists to discover evolutionary relations between sponges. As a matter of fact, they can be classified according the skeletal structure in calcareous sponges (Calcarea; with calcareous spicules), glass sponges (Hexactinellida; with siliceous spicules), and common sponges (Demospongiae; with siliceous spicules and spongin).
Sponges are useful animals
Although the coralline sponges (Sclerosponges) belong to the common sponges, they have one distinct treat: their massive basal skeleton. This makes them interesting to many researchers, since skeletons can build up a record of earlier climatic changes (see http://www.vub.ac.be/calmar/general.htm (*)).
Other common sponges are better known in bathing places: their spongin fibres can hold as much as 40 % of their own weight in water. Before the production of synthetic sponges, these sea sponges were bred at the coast, buy cutting a sponge into pieces and hanging it in the water. Every piece grew into a complete new bath sponge! Bath sponges are still bred in places, for they are much better than their imitations.
Sponges are especially coveted by pharmaceutical industries in the last decades. Researchers are interested in the abundant bioactive compounds produced by sponges that can be used as new medicines.
Among all marine animals, the invertebrates are those that contain most chemical substances that might be useful to humans. And among all invertebrates, the sponges are the champions in this field! New substances with antibiotic or fungicidal properties are often found in sponges harvested all over the world. There are 10,000 known different species of sponges, but new species are discovered frequently.
(*): This website is only available in english and will open in a new window.
