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(horny sponges), a group of invertebrates of the order Cornacuspongida. Horny sponges measure up to 1 m high. The skeleton consists of horny (spongin) fibers. There is no mineral skeleton proper, but often the fibers contain foreign inclusions, such as grains of sand, pieces of needles from other sponges, and the shells of protozoans. Horny sponges are distributed predominantly in shallows of the tropical and subtropical seas. There are about 40 genera, including Euspongia, Hippospongia, Verongia, and Hircinia. Five species are found in the seas of the USSR. Bath sponges, which are commercially valuable, belong to Keratosa.