A new species of Elpidium Müller, 1880 (Crustacea, Ostracoda) from Hispaniola, with an updated key to the species of the genus, and its molecular phylogenetic positioning within the Cytheroidea

The ostracod genus <i>Elpidium</i>, a specialist of phytotelma habitats, has received increased attention during the past decade, with a proliferation of described species, rising from seven to nineteen. These recent studies emphasize the high diversity and endemicity of the genus, and its wide distribution in the Neotropics. Yet many regions are still to be inspected for the presence of <i>Elpidium</i>. In this work, a new species collected from Hispaniola is described, for which only undetermined previous records existed, despite several species being known from the neighboring islands of Cuba, Jamaica, and Puerto Rico. <i>Elpidiumalarconi</i> <b>sp. nov.</b> belongs to the group with a basal expansion on the hemipenis distal lobe, which contains six other species (<i>E.chacoense</i>, <i>E.cordiforme</i>, <i>E.higutiae</i>, <i>E.maricaoense</i>, <i>E.merendonense</i> and <i>E.picinguabaense</i>) and can be distinguished from them by the different shape of the basal expansion (appearing long and digitiform) and by a thin, pointed and L-shaped lower ramus. An updated key is constructed to allow identification of the 20 species of <i>Elpidium</i> described to date, based on shell morphology and soft parts anatomy. The first sequence of the molecular marker 18S for a described species of <i>Elpidium</i> is also presented, and shows its close affinities to members of the genera <i>Gomphodella</i>, <i>Metacypris</i>, and <i>Cytheridella</i>, all in the same clade, separated from the branch where <i>Limnocythere</i> is positioned in the phylogenetic tree. These molecular results, together with strong morphological differences, support the promotion of the subfamily Timiriaseviinae to the family rank, independent from the Limnocytheridae, to which it formerly belonged.