A solitary sea squirt with a tough leathery tunic covered in short spines, orange to reddish, its two siphons frequently ringed in a paler shade. It grows singly on rock and dead coral, up to about 10 cm (4 in) tall, and is stiff enough to keep its shape out of water.
The tunic is the feature that names the whole subphylum: it is built largely of cellulose, which no other animal produces, and it functions as armour, anchor and skeleton at once. The spines add grit to that defence, and the result is an animal almost nothing eats. Water is drawn through a pharyngeal basket pierced by thousands of slits, and everything edible in it is trapped on a moving sheet of mucus - a filtering method so effective that a colony of sea squirts can clear a measurable fraction of the water passing over a reef.
- tough leathery body covered in short spines
- orange to reddish, siphons often ringed paler
- grows singly, firmly attached to rock
- height up to 10 cm
