Sollas, 1888
Definition: There is only a single family in the order, the Family Plakinidae (in which the family Oscarellidae is included (following Diaz and Van Soest, 1994). It includes thinly to thickly encrusting sponges. The skeleton is formed by a combination of calthropses, which may or may not have lophate rays (then dubbed lophotriaene), and/or reduced derivated (diods and triods). These are generally arranged uniformly in the body, and usually surrounding the aquiferous system in a very regular "aveolar" way. Specialized spiculation (candelabras, microrhabds, etc.) may be added to the basic spiculation. Loss of siliceous skeleton is found in one genus (Oscarella ), but has recently been registered also in local population of the spicule-bearing genus Corticium . In 1995 a new genus was erected for this material, Pseudocorticium Boury-Esnault and Muricy. Large choanocyte chambers mostly eurypyllous and the group has a unique amphiblastula-like larva. They occur mainly in warm waters.
Source: Diaz and Van Soest, 1994.