Desmanthus meandroides n. sp. is described from São Sebastião, SW Brazil and D. levii n. sp. from the Pacific coast of Panama. Assignment of the new species to the «sublithistid» genus Desmanthus Topsent, 1893 followed after critical comparison of species of Desmanthus with Lophacanthus rhabdophorus Hentschel, 1912. In addition to ectosomal erect styles and a basal mass of undifferentiated desmas I, the new species share the possession of subectosomal desmas II provided with prominent outward-facing rhabdomes with L. rhabdophorus. However, desmas II with a less prominent but nevertheless clearly developed rhabdome were also discovered in the type species of Desmanthus, D. incrustans (Topsent, 1889). The alleged difference between the two genera appeared thus to be a matter of grade and a clear discriminatory character was found lacking. Accordingly, it is proposed to consider Lophacanthus a synonym of Desmanthus. The genus Desmanthus now contains six species, together occurring in all tropical regions as well as in the cooler waters of the Mediterranean (one species) and in South East Atlantic (one species). The latter species, D. macphersoni Uriz, 1989, has peculiar ectosomal spicules and is suspected to belong to a separate undescribed genus. The higher taxa classification of Desmanthidae is controversial because of lack of similarity to other lithistid groups and the inclusion by some authors of a second genus with characters similar to those of Desmanthus, i.e. Lithobubaris Vacelet, 1969. Type material of L. tenens and a Caribbean specimen assigned to the same species by Van Soest & Stentoft 1988 were studied to determine the degree of similarity with Desmanthus. L. tenens sensu Van Soest & Stentoft, 1988 was distinguished from L. tenens at the species level and a new species L. leviorum n. sp. was erected. The ordinal relationships of the genera Desmanthus and Lithobubaris are considered and various alternative positions are discussed, including Vacelet’s (1969) proposal to assign Lithobubaris to the halichondrid family Bubaridae. A tentative assignment of Desmanthus and Lithobubaris to a single family Desmanthidae Topsent, 1893 in the «lithistid» group of Anoplia is preferred pending further new data.
Porifera, sublithistid, Desmanthus, Lophacanthus, Lithobubaris, new species.