Biodiversity assessment of the Lower Mekong Basin: A new species of Corvospongilla (Porifera: Spongillina: Spongillidae) from Thailand

Only six species (four genera, one family) of freshwater sponges are known until now from Thailand. A first record of the genus Corvospongilla Annandale, 1911 with the description of a new species is here reported from the Pong River in the Lower Mekong Basin. The taxonomic status of Corvospongilla siamensis nov. sp. is discussed in comparison to the 18 species assigned to the genus. The new species is characterised by i) alveolate, paucispicular skeletal network with scanty spongin, thick ascending tracts towards the sponge surface to support conules; ii) skeleton of stout microspined strongyles, and extremely rare, abruptly pointed oxeas usually with a few tubercles, plus micropseudobirotules with smooth shaft; iii) gemmules belonging to a single gemmular morph, typically sessile; iv) gemmular cage notably stout, of tangentially arranged strongyles of variable length from tubercled to spiny; v) gemmular theca with abundant laminar compact spongin, lacking pneumatic layer, armed by short, tubercled to spiny strongyles tangentially embedded; vi) larvae armed by spiny oxeas. Corvospongilla siamensis nov. sp. differs from all the other known species of the genus in its unique combination of diagnostic traits, particularly a) acanthostrongyles (megascleres), b) gemmuloscleres, both in the cage and in the theca, as strongyles showing the tendency towards ring-shape and button-like shape, and c) larval spiny oxeas.