Integrative Description and Redescription of Black Fly (Diptera: Simuliidae) Species in the Simulium (Gomphostilbia) ceylonicum Species-Group from Thailand

Utilizing the <i>COI</i> barcoding approach, cryptic diversity has previously been detected within the morphologically recognized <i>Simulium</i> (<i>Gomphostilbia</i>) <i>trangense</i> Jitklang, Kuvangkadilok, Baimai, Takaoka & Adler, 2008 and <i>S.</i> (<i>G</i>.) <i>sheilae</i> Takaoka & Davies, 1995, of the <i>S.</i> (<i>G.</i>) <i>ceylonicum</i> species-group. Here, an unknown black fly species belonging to the <i>S. ceylonicum</i> species-group from southern Thailand was discovered and described as a new species, <i>S.</i> (<i>G.</i>) <i>sipoense</i> sp. nov. In addition, <i>S.</i> (<i>G.</i>) <i>trangense</i> 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 <i>S. sipoense</i> sp. nov. and the redescribed <i>S. trangense</i> is confirmed. Comparative morphological characteristics and phylogenetic analysis, inferred from <i>COI</i> sequences, suggest that the new species is conspecific with the species redescribed as <i>S. trangense</i>, using specimens collected from Malaysia, and is morphologically and phylogenetically closely related to <i>S. sheilae</i>, particularly to the specimens from Indonesia. The redescribed <i>S. trangense</i> is genetically highly similar or even identical to the species that was apparently misidentified as <i>S. sheilae</i> 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 <i>S. trangense</i> 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 <i>S. trangense</i> and <i>S. sheilae</i>.