Taxonomy of Melophlus Thiele, 1899 and Stellettinopsis Carter, 1879, with description of two new species from Brazil (Demospongiae: Astrophorina)

In the present study, the demosponge genus Melophlus Thiele, 1899 is revised and the type specimens of all its species are re-examined. The diagnosis of the genus is amended, based on the presence in the type species, M. sarasinorum Thiele, 1899 , of a well-developed ectosome of acanthomicrorhabds and a dense feltwork of large oxeas, together with oxyasters and microxeas as microscleres; triaenes are absent. Melophlus ruber Lehnert & van Soest, 1998 and Melophlus hajdui Moraes, 2011 are here transferred to Stellettinopsis Carter, 1879 due to their superficial crust of large acanthomicrorhabds, bouquets of oxeas in the ectosome, and rare triaenes previously overlooked. Additionally, we describe two new species of Stellettinopsis from Brazil and compare them to all valid species of the genus. Stellettinopsis capixaba sp. nov. is distinguished from its congeners especially by the presence of rare orthotriaenes with curved cladi and of three categories of spined euasters (oxyasters 1 and 2 and strongylasters); Stellettinopsis baiana sp. nov. is characterized mainly by the common orthodichotriaenes, spined oxyasters, and spined strongylasters. Stellettinopsis species have been often assigned to the genus Melophlus due to their similar spicule complement and rarity of triaenes. We suggest that skeletal architecture and the shape of microscleres are more useful than megascleres to separate genera with rare triaenes such as Stellettinopsis and Stryphnus from other astrophorids. Morphological data suggest that both Stellettinopsis and Melophlus should be re-allocated to the family Ancorinidae, but more comprehensive integrative studies are still needed to resolve the classification of Astrophorina.