Instead they arrange themselves in star shaped colonies, on rocks or seaweed on the shore and in the shallows, in a communal gelatinous casing which can cover an area up to 15 cm across. This casing is called a 'tunic' or 'test' which encrusts the substrate. At the centre of each star is a shared exhalent opening through which water is expelled. The colonies very greatly in colour and may be green, violet, brown or yellow with the individuals having a contrasting colour to the test.
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