A new species of Megadiaptomus Kiefer, 1936 (Copepoda: Calanoida: Diaptomidae) from the Western Ghats of India, with notes on the biogeography and conservation status of the species of the genus

Megadiaptomus montanus n. sp. is described based on plankton samples collected from temporary water bodies in the Western Ghats of Maharashtra state, India, a mega-diverse region and biodiversity hotspot in west-central India. This is the third species of Megadiaptomus Kiefer, 1936, the other two being M. hebes Kiefer, 1936 from Sri Lanka and southern India and M. pseudohebes Ranga Reddy, 1988 from south-eastern India. All three species are large-sized inhabitants of temporary waters having a rather restricted distribution on the Indian subcontinent, and are presently facing increasing anthropogenic pressures. By IUCN criteria they are assignable to the Critically Endangered category (CR B2). The new species can be easily distinguished from its congeners in that the males have a short, spinous process on the antepenultimate segment of the right antennule; the second exopodal segment of the right leg 5 (P5) has a proximal, quadrate accessory process; and the inner apical spiniform process of the left P5 is greatly transformed, a remarkable apomorphy for the family Diaptomidae Baird, 1850. The urosome has three somites in the female, and the coxal spines of the P5 are large and asymmetrical. The salient characters and their different states in the three species of Megadiaptomus, in contrast to those of the other Indian species of Diaptomidae, are briefly discussed. Notes on the biogeography, ecology, and conservation status of the species of Megadiaptomus are also given.