Giant Barrel SPonge (xestospongia muta)
Xestospongia muta, commonly known as the giant barrel sponge, a member of the Xestospongia genus, is one of the largest species of sponge found in the Caribbean. It grows at depths from 10 meters down to 120 metres (390 ft), and can reach a diameter of 1.8 metres (6 feet). It is brown-grey to reddish in colour, with a hard or stony texture. There is little scientific information about the species, although it has been monitored since 1997. Xestospongia muta has been called the "redwood of the reef" because of its lifespan of up to 2000 years as well as its size and color. Xestospongia muta is somewhat variable in form. Typically it is barrel-shaped, with a cone-shaped cavity at the apex known as the osculum. In some locations, perhaps because of prevailing currents, it may be oval, elongate or irregular in cross section. The surface is rough, rugged, and irregular, often with buttresses, and hard in texture. The sponge grows slowly to a very large size, and a large specimen might weigh 80 kilograms (180 lb). In shallow water the colour is dark brown, but at greater depths the sponge is paler; at its maximum depth of 120 metres (390 ft) it is white, sometimes suffused with pink.
structure
Xestospongia muta is a filter feeder. Water is continually being pumped through the interior of the sponge. Small pores in the body wall are connected to channels lined by cells with flagella, and the rhythmical beating of these draws water through the channels. Incoming particles such as bacteria, viruses, diatoms and minute particles of organic debris lodge in the increasingly narrow channels, and are phagocytosed by cells in the channel wall. The water leaves the sponge through the osculum.