Two new species of Nitocrella (Copepoda, Harpacticoida) from a spring in Loei Province, northeastern Thailand

Two new species of the genus <i>Nitocrella</i> are described from a karstic spring in Loei Province, northeast Thailand. They are the first representatives of the genus <i>Nitocrella</i> Chappuis, 1924, described from Thailand. <i>Nitocrellagrandicaudis</i> <b>sp. nov</b>. and <i>N.thailandensis</i> <b>sp. nov</b>. show the peculiar shapes of the inner element of the male P1 basis, the basis of the mandible, and the proximal endite of the maxilla, differing from their congeners. While <i>N.grandicaudis</i> <b>sp. nov.</b> belongs to the <i>chappuisi</i> group according to the absence of a proximal inner seta on the third exopodal segment of the fourth swimming leg, <i>N.thailandensis</i> <b>sp. nov.</b> belongs to the <i>vasconica</i> group because the seta is present on the segment. Despite the low degree of differentiation in morphological characters, the shape of the female caudal ramus and the proximal seta of the male fifth segment of the antennule suggest that <i>N.grandicaudis</i> <b>sp. nov.</b> differs significantly from the other new species in its mating behavior. A detailed description and illustrations of two new species are provided, as well as a discussion on the divergence of both new species. Some comments on the basic understanding of the reproductive behavior of Harpacticoida are included.