Reassessing the species status of Pseudodiaptomus malayalus Wellershaus, 1969 and P. binghami Sewell, 1912 (Calanoida: Pseudodiaptomidae) from India based on morphology and mitochondrial cytochrome oxidase I gene sequences

Pseudodiaptomus binghami Sewell, 1912 was first described from the Rangoon River (now Yangon River) estuary, Myanmar. Pseudodiaptomus malayalus Wellershaus, 1969 previously known as P. binghami malayalus, is a typical brackish-water calanoid copepod from Cochin Estuary, Kerala. Morphological examination of P. malayalus and P. binghami collected from Cochin Estuary and the Nambur canal in Andhra Pradesh revealed crucial differences between the two congeners. Female specimens of P. malayalus exhibited marked differences from those described by Wellershaus. They are (1) the number of terminal spines on P5, (2) ornamentation of GS, (3) ornamentation of Ur1-4, (4) length ratio of the Ur and CR segments and (5) length: width ratio of the CR setae. Furthermore, significant and discrete morphological differences were observed between the two Indian species in their P5 and urosome. But the male specimens of P. malayalus did not show any major differences from the original description. In addition, distance matrix data revealed 22% interspecific divergence values which in turn confirmed the status of P. malayalus and P. binghami as two distinct species.