Although they are soft and boneless, ascidians are not invertebrates, but primitive chordates, the phylum to which all back-boned animals belong. Ascidians are filter feeders. Fresh seawater is drawn into the branchial basket through the inhalent siphon and filtered seawater and waste material is ejected through an exhalent siphon. The common name Sea Squirt , arises from their habit of squirting a jet of water, when you stand on or near them when they are uncovered at low tide. Most solitary ascidians are attached either along one side of their bodies or at the base, but their are some species which are attached by stalks, sometimes 2 or 3 times their body length.
Many ascidians form colonies.
In the intertidal zone, many of the fleshy, brightly coloured patches under rocks or in shaded crevices are ascidian colonies. Ascidians are an important food source for some nudibranchs. Species of Goniodoris , such as G. meracula , and Nembrotha , such as N. kubaryana , feed on specific ascidian species.