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a family of sponges of the order Tetraxonida (four-rayed sponges). Clionids are capable of boring winding passages into a solid limestone substrate. They are usually found in the shallow waters of warm and temperate seas. There are about 20 species. In the USSR species have been found in the Sea of Japan and in the Black, White, and Barents seas. It is believed that the drilling mechanism of clionids consists in the secretion of carbon dioxide by certin superficial cells, as well as mechanical actions of the cells. Clionids are dangerous pests of oyster beds: they cause a fatal disease of oysters by settling on the shells and boring passages in them. One of the methods to control the disease is the immersion of affected oysters in fresh water for a short period of time.