Family Theonellidae Lendenfeld, 1903

Abstract

Theonellidae Lendenfeld (Demospongiae, ‘lithistids’) contains five genera and about 50 nominal species (most poorly known) occurring both in shallow and deep waters worldwide. They are polymorphic, ranging from thin encrusting to massive irregular, cylindrical, erect- branching, cup-shaped or clavate, with or without axial cavity. Theonellidae are characterized by ectosomal phyllotriaenes and/or disco- triaenes, choanosomal tetraclones and microscleres as acanthorhabds to pseudospherasters and/or microxeas, and/or streptasters/ amphiasters. Genera are differentiated based on the type of ectosomal spicules and microscleres, as well as habitus. This family is basi- cally Recent, but it corresponds to the family Discodermiidae Schrammen of paleontologists, which has numerous genera known since the Cretaceous, and is here considered as a junior synonym of Theonellidae.