Diversity of sessile rotifers (Gnesiotrocha, Monogononta, Rotifera) in Thale Noi Lake, Thailand PHURIPONG MEKSUWAN (Thailand), PORNSILP PHOLPUNTHIN (Thailand) & HENDRIK SEGERS (Belgium)

In response to a clear gap in knowledge on the biodiversity of sessile Gnesiotrocha rotifers at both global as well as regional Southeast Asian scales, we performed a study of free-living colonial and epiphytic rotifers attached to fifteen aquatic plant species in Thale Noi Lake, the first Ramsar site in Thailand. We identified 44 different taxa of sessile rotifers, including thirty-nine fixosessile species and three planktonic colonial species. This corresponds with about 40 % of the global sessile rotifer diversity, and is the highest alpha-diversity of the group ever recorded from a single lake. The record further includes a new genus, Lacinularoides n. gen., containing a single species L. coloniensis (Colledge, 1918) n. comb., which is redescribed, and several possibly new species, one of which, Ptygura thalenoiensis n. spec. is formally described here. Ptygura noodti (Koste, 1972) n. comb. is relocated from Floscularia, based on observations of living specimens of this species, formerly known only from preserved, contracted specimens from the Amazon region. In addition, ten of the species recorded are added to the fauna of the Oriental region, twenty-seven are new to Thailand.