Marine Sponges - The Marine Diaries

So what exactly are marine sponges?

Named purely by their appearance, sponges are from the phylum Porifera. There are over 11,000 described species and 9000 living species. Around 150 of these live in freshwater and the rest are found in the ocean or brackish water. Genetic analysis has revealed they are the most primitive (still have very similar characteristics found at the beginning of their evolutionary history) animal group alive today, and are probably some of the first animals to ever appear on the earth.

How do we know this? A team of scientists led by Dr Gordon Love analysed fossils of sponges for traces of a steroid biomarker produced by a common class of sponges (the demosponges). The fossils containing this biomarker were dated to be at least 635 million years old! It’s believed that they dominated the oceans as the main reef builders 400 million years ago (a responsibility hard corals have taken over in present day). How can soft animals be reef builders you may ask. Well, they eventually fossilised into hard rock and were used to build castles in the middle ages.

All sponges are aquatic (found in water), completely sessile (non-motile/ do not move) and filter feeders. However the larvae of sponges are motile and free swimming in the plankton, until they settle on a substrate, turn themselves inside out and begin to grow. Most are marine and are found from the intertidal to abyssal zone (at depths of 3000- 6000m) which is in complete darkness).

Quick facts

Size range: ½ inch → 6 ft. tall (The Loggerhead Sponge being the largest!)

Shape: Round / flat / encrusting / vase-like

Colour: Often brightly coloured, given by the pigments in the surface cells!

Body plan:

• Their body is a network of pores, canals, and passageways

• They have no ‘mouth’

• They have no nervous system, so they are the only animals that don't react when disturbed

• Water is pumped into holes called ostia to filter out the nutrients

• Water exits through larger openings called oscula

• The large chamber is called the spongocoel

• They have to filter 1 ton of water to get 1 oz of food (the size of 2 tablespoons!)

• They control the flow of water by constricting the osculum at night and opening it in the day when food is more plentiful

• They also reverse the flow to clean out their canals after a storm