Carpet sea squirt

Description

A colony of Didemnum vexillum consists of a number of sac-shaped zooids connected by a common tunic.Each zooid is about 1 mm (0.04 in) long and has a buccal siphon through which water is drawn into the interior.The water then passes into a shared cavity from which it is pumped out through an atrial siphon.The surface of the colony is smooth,leathery,and often veined in appearance;the buccal siphons appear as numerous fine pores,and the atrial siphons as a smaller number of larger holes.The colony is firmly attached to a hard surface from which it can be difficult to detach D.vexillum has different forms in different locations.It can form a thin or thick encrusting mat,or form large or small lobes.The colour can be orange,pink,tan,creamy yellow or greyish-white and the tunic is sparsely strengthened by stellate spicules with nine to eleven rays.Where there is little water movement,the colonies may dangle in ropey masses from hard substrates,such as cables,docks,and the hulls of vessels.These stringy formations have led to it being colloquially referred to as "Sea Cheese" in Canada.In places with stronger currents,they cover the surface of rocks,boulders,pebbles,gravel,and oysterbeds in a thin,encrusting layer