First records of the genera Mariaplax Rahayu & Ng, 2014 and Hexapinus Manning & Holthuis, 1981 from India, with descriptions of three new species (Crustacea, Decapoda, Brachyura, Hexapodidae)

Three new brachyuran crab species of Hexapodidae are described from the Arabian Sea and Bay of Bengal, based on material collected by FORV Sagar Sampada between 2015 and 2019, with the genera Mariaplax Rahayu & Ng, 2014, and Hexapinus Manning & Holthuis, 1981, reported from Indian waters for the first time. Mariaplax kochazhi sp. nov ., and M. albucus sp. nov . were collected from the Arabian Sea at a depth 30 m while Hexapinus clivus sp. nov . was collected from the Bay of Bengal. Mariaplax kochazhi sp. nov . is most similar to M. granulifera (Campbell & Stephensen, 1970) from Australia but can be distinguished by its proportionately wider carapace with the surfaces possessing larger granules, the pterygostomial region smooth with 5–7 striae, a rectangular ischium and more granulated merus of the third maxilliped, a subpentagonal male pleon telson, and a strongly curved S-shaped male first gonopod with a rounded distal tip. Mariaplax albucus sp. nov . is similar to M. sundaica Rahayu & Widyastuti, 2018, from Java, but can easily be differentiated by a carapace that is as long as wide, a pterygostomial region that has 6 oblique striae, a relatively shorter and stouter P4 merus (4.0 times wider than long) and the distinctive structure of the vulva. In the latter species, the vulval operculum cover differs markedly from M. kochazhi , which is simple, rounded, and lacks a cover. Hexapinus clivus sp. nov . is morphologically close to the widely distributed H. simplex Rahayu & Ng, 2014, from the West Pacific, but it can easily be differentiated by the weaker granulation on the carapace surface; possession of a relatively shorter and stouter P4 merus (2.5 times as long as wide); a proportionately wider male thoracic sternum, with the fused sternites 1 and 2 being subtriangular and the lateral margins gently sloping; and the semilunate vulva elevated and protruded, and positioned adjacent to the suture between sternites 5 and 6.