Abstract
Utilizing the COI barcoding approach, cryptic diversity has previously been detected within the morphologically recognized Simulium (Gomphostilbia) trangense Jitklang, Kuvangkadilok, Baimai, Takaoka & Adler, 2008 and S. (G.) sheilae Takaoka & Davies, 1995, of the S. (G.) ceylonicum species-group. Here, an unknown black fly species belonging to the S. ceylonicum species-group from southern Thailand was discovered and described as a new species, S. (G.) sipoense sp. nov. In addition, S. (G.) trangense is herein fully redescribed based on specimens collected from its type locality. Based on an integrative taxonomic approach combining morphological and molecular data, the validity of the newly described S. sipoense sp. nov. and the redescribed S. trangense is confirmed. Comparative morphological characteristics and phylogenetic analysis, inferred from COI sequences, suggest that the new species is conspecific with the species redescribed as S. trangense, using specimens collected from Malaysia, and is morphologically and phylogenetically closely related to S. sheilae, particularly to the specimens from Indonesia. The redescribed S. trangense is genetically highly similar or even identical to the species that was apparently misidentified as S. sheilae from southern and western Thailand, and is morphologically very similar to the new species, from which it is clearly distinguished by the relative length of the female claw tooth, shape of the male ventral plate, and color of the larval body. A detailed information on the morphological characteristics separates the new species, and the redescribed S. trangense from all other known species of the same species-group in Thailand and neighboring countries is provided. Further studies are warranted to clarify the taxonomic status of several cryptic species recognized within the morphologically defined S. trangense and S. sheilae.