Molecular phylogeny and taxonomic position of Macrobrachiumlanchesteri (De Man, 1911), with descriptions of two new species from Thailand (Decapoda, Caridea, Palaemonidae)

(De Man, 1911), a translucent freshwater prawn has a wide distribution range throughout mainland Southeast Asia. A high morphological variation and genetic divergence between different geographical populations in Thailand have peculiarly extended the uncertainty of species boundaries and blended confusingly with several species. To clarify these circumstances, broad sample examinations of the morphological variation, including topotype specimens, and phylogenetic reconstruction based on the concatenated mitochondrial dataset (16s rRNA and COI genes) were performed. Broad morphological examination of has shown congruency with phylogenetic analyses by revealing prominent lineages of sensu stricto and two new sibling lineages with interspecific variation between 6.48-8.76% for COI and 3.06-4.23% for 16S. Descriptions of two new species, named herein as Chaowvieng & Siriwut, and Chaowvieng & Siriwut, are provided. Morphological investigation of rostral form suggested plasticity in populations showing the morphological trait associated with their habitat preferences. Furthermore, phylogenetic positions of the three taxa affirmed the hidden diversity of Thai freshwater fauna correlated with the river network in the Mekong and Chao Phraya basins, Thailand. The genetic data and distribution records obtained in this study may also assist future river conservation plans as well as the sustainable management of freshwater prawn diversity.