Colonial Pelagic Tunicate

Description:

A colony of P. atlanticum is cylindrical and can grow up to 60 cm (2 ft) long and 4–6 cm wide. The constituent zooids form a rigid tube, which may be pale pink, yellowish, or bluish. One end of the tube is narrower and is closed, while the other is open and has a strong diaphragm. The outer surface or test is gelatinised and dimpled with backward-pointing, blunt processes. The individual zooids are up to 8.5 mm (0.3 in) long and have a broad, rounded branchial sac with gill slits. Along the side of the branchial sac runs the endostyle, which produces mucus filters. Water is moved through the gill slits into the centre of the cylinder by cilia pulsating rhythmically. Plankton and other food particles are caught in mucus filters in the processes as the colony is propelled through the water. P. atlanticum is bioluminescent and can generate a brilliant blue-green light when stimulated

Habitat:

P. atlanticum is found in temperate waters in all the world's oceans, usually between 50°N and 50°S. It is most plentiful at depths below 250 m (800 ft).[4] Colonies are pelagic and move through the water column. They undergo a large diurnal migration, rising toward the surface in the evening and descending around dawn. Large colonies may rise through a vertical distance of 760 m (2,500 ft) daily, and even small colonies a few millimetres long can cover vertical distances of 90 m (300 ft).