Calcarea

(or Calcispongiae), an order of marine invertebrate sponges. The skeleton of these sponges is formed from three-rayed, four-rayed, or uniaxial calcareous spicules. The structure of the canal system varies; all three types are encountered (ascon, sycon, and leucon). The Calcarea are small (usually no more than 7 cm high) individual or colonial animals. The body often has a tubular or barrel-like shape. The sponges live mainly in shallow waters. There are approximately 100 species in the order. There are more than ten species in the Soviet seas; the most common genera are Leucosolenia, Sycon, and Leucandra.