Nearly everyone is familiar with sea anemones.
These common inhabitants of our rockpools have a simple but effective body plan: a hollow, stubby, cylinder with a toothless mouth at the top. Sometimes, most of the body is hidden in crevices in the rock or sand. Surrounding the mouth are rings of tentacles covered in stinging cells, ranging from speckled white to brown and green; the waratah anemone has bright red ones.
Fortunately for children who love to touch and watch the animal withdraw its tentacles inside its body, the stinging cells of intertidal anemones are not harmful to us tough-skinned humans. They just feel sticky. However they are very effective at killing or immobilising small fish and crustaceans the anemones eat.
At the other end of the alphabet are close relatives, the zoanthids, usually found in deeper water and mostly colonial. Each animal resembles an elongated sea anemone and has one or two rings of short, smooth tentacles around its mouth. The animals in the colony grow close together, connected by stolons of flesh.
Snorkellers can sometimes come across a colony of the finger zoanthid. Individuals grow to about 8cm and feed at night, so they are usually seen bent over with tentacles retracted. The colony looks a bit like a muddle of grey-green mini sausages covering the bottom. Search the deep part of the Pot at Guerilla Bay when the water is calm and clear.
The Yellow Zoanthid is more spectacular. It is often seen by divers on coastal reefs on shaded rock surfaces or in dark overhangs growing on an encrusting sponge. In well-lit waters it cannot compete for space with algae. The body and tentacles are yellow. Orange lines radiate from the mouth to the tentacles and there is a small red dot at one end of the mouth.
The Nature Coast Marine Group has an extensive program to have fun learning about our marine environment. Visit www.ncmg.org.au or search for Nature Coast Marine Group on Facebook.