Biodiversity assessment in the Lower Mekong basin: First record of the genus Oncosclera (Porifera: Spongillina: Potamolepidae) from the Oriental Region

Taxonomic richness of Thai Spongillina numbers so far seven species (five genera, one family). The first record of the genus Oncosclera Volkmer-Ribeiro, 1970 belonging to the family Potamolepidae Brien, 1967 is here reported with the description of a new species from the Pong River (NE Thailand, Oriental Region) in the framework of a biodiversity assessment in the Lower Mekong Basin. An emended diagnosis of the genus is also provided. The new species, ascribed to the genus Oncosclera for diagnostic traits of the skeleton and the gemmular architecture, differs from all the other known species of the genus in its unique combination of diagnostic traits. O. asiatica sp. nov. is characterised by i) more or less alveolate skeleton, ii) conulose surface with a network of branched subdermal canals, iii) acanthoxeas as dominant megascleres and less frequent acanthostrongyles, iv) gemmular theca sublaminar of compact spongin with a scantly developed pneumatic layer of fibrous spongin, and v) gemmuloscleres as acanthostrongyles from elongated to ovoid with tubercles/spines particularly dense towards the tips. Despite the extremely disjunct distribution O. asiatica is morphologically similar to O. intermedia and O. jewelli from the Neotropical Region and O. gilsoni from Pacific Islands, from which the former diverges for megascleres and/or gemmuloscleres traits.