A small order of sponges of the class Demospongiae, subclass Ceractinomorpha, with a skeleton of diactinal or monactinal siliceous megascleres or both. Some megascleres may be arranged in loose tracts, but most are distributed irregularly in the flesh. Spongin is present in small amounts; microscleres are absent. A skinlike dermis is present and is often reinforced with tangentially placed spicules.