Hadodiaptomus dumonti n. gen., n. sp., a new freshwater stygobitic calanoid (Crustacea: Copepoda: Calanoida) from Vietnam (South Asia) and a new member of the subfamily Speodiaptominae Borutzky, 1962

A new species of freshwater stygobitic calanoid, Hadodiaptomus dumonti n. gen., n. sp., from a cave in Vietnam (South Asia) is described. It is the ninth taxon from the order Calanoida described from freshwater subterranean (i.e. cave) environments. It is the fourth member of the subfamily Speodiaptominae Borutzky, 1962. It differs from stygobitic taxa in Europe and Mexico by numerous characters, especially in the armature of P1–P5, antenullas, mouth parts and genital segments in both sexes. Arthrodial membrane development from CII to CV is different from epigean as well as from subterranean taxa. These differences suffice to raise a new genus–Hadodiaptomus, characterised by two-segmented exopodites and endopodites of P1–P4 and reduced P5 endopodites in both sexes. Males are without widened segments 13–18 on right A1. Relations with other stygobitic taxa of the subfamily Speodiaptominae are discussed.