Feather Starfish Red

These feathery animals are sometimes seen on some of our shores, generally near living reefs. They are also encountered by divers on our Southern reefs.

What are feather stars? Feather stars belong to Phylum Echinodermata. Although they may look similar to brittle stars, feather stars belong to a different Class Crinoidea. 'Crinoidea' means 'lily-like' in Greek. There are about 600 known living species of feather stars. Shallow-water crinoids are also called comatulids.

Features: Like other echinoderms, feather stars are symmetrical along five axes, have spiny skin and tube feet. Like brittle stars, feather stars have thin, long and highly flexible arms. But crinoids are much more spectacular than brittle stars, with an explosion of long feathery arms.

The arms arise from a cup-shaped structure at the centre called the calyx. The calyx contains the digestive system and is covered by a soft membrane called the tegmen that may be rounded into a mound or look like a drum skin over the calyx. Unlike sea stars and brittle stars, the feather star's mouth facing upwards. The mouth may be in the centre of the disk or off to one side. The anus is also on the upperside, in some species at the top of a cone or tube that brings it above the feeding current to prevent fouling of the feeding process. The side of the feather star that faces downwards has a claw-like appendage called the cirri that is used to grip the surface.

Sometimes confused with brittle stars which also have bristley arms. But brittle stars usually only have 5 or 6 arms. More on how to tell apart bristley animals and feathery animals.

An armful: Juvenile feather stars start with 5 arms but repeatedly grow back two arms in place of each arm branch that is shed. This branching happens near the calyx. Thus feather stars usually have arms in multiples of 5, most have at least 10 arms. Some can have 80-200 arms!

The arms are made up of large, well developed, jointed ossicles (plates made mostly of calcium carbonate). The ossicles are connected together like a bicycle chain. Along the length of the arms are rows of tiny finger-like structures called pinnules that give the animal its feathery look. Each pinnule is jointed and has a groove down the middle that joins to a groove running down the length of the arm. The grooves are lined by tube feet that produce mucus. Unlike in sea stars, the tube feet do not play a part in moving the animal but are used in collecting food and to breathe. The pinnules near the mouth protect the mouth from harm and keep the area clean.

What do they eat? Feather stars feed on tiny drifting organisms and particles, gathering these passively from the water by adjusting their arms to maximise the filter feeding area relative to the water flow. The arms may form a flat fan or may be curved into a parabola like a satellite dish. Some may hide in crevices and only stick out some part of their arms to gather food. The mucus covered arms have tiny tube feet that flick edible bits into the grooves of the pinnule and arm. These bits are then slowly transported along the groove to the mouth.

1-3 inches in size

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