July 2012

Unusual creature washes up on a beach.

I was hoping you can help identify this creature. I photographed it on the beach just south of the border (Kingscliff), it was about 4 inches long and felt rubbery like a sea sponge. Posting the picture to Facebook caused some odd reactions!

Answer

Sea anemone (Sphenopus marsupialis). Photographed by Kylie Ann Burchell.

The creature shown in the photograph is a type of free living solitary zoanthid, most likely the species Sphenopus marsupialis. Zoanthids are simular to small sea anemones; however, the one in this photo has retracted its tentacles inside the body. The smaller end, where you can see a crease, is the ‘mouth’ that opens to reveal the tentacles.

S. marsupialis have been recorded from marine habitats across the world. Like many other zoanthids, the outer skin has sand grains embedded into it giving it a thick rubbery-like appearance. It is believed that this sand helps the zoanthis anchor on sandy or muddy bottoms. Unlike other zoanthids which are colonial or encrusting, S. marsupialis has the ability to move around, although this is very slow. Zoanthids feed both by photosynthesis (aided by zooxanthellae), and by filtering plankton and organic matter from the water.

You don’t usually see these washed up on beaches. During heavy storms or rough weather, they sometimes dislodge from the sediment. Once pushed into the water currents, they are at the mercy of the waves.

Queensland Museum's Find out about... is proudly supported by the Thyne Reid Foundation and the Tim Fairfax Family Foundation.