Heteropolyonyx, new genus (type species: H. biforma new species), is established on the basis of the presence of transverse ridges on the cervical regions of the carapace and the telson being divided into five plates, characters quite different from its related genera Polyonyx Stimpson, 1858, and Eulenaios Ng and Nakasone, 1993. The male/female pair of H. biforma was found in a tube of an unidentified polychaete of the genus Chaetopterus. Polyonyx utinomii Miyake, 1943, is redescribed from the holotype specimen and recently obtained material from Japan and the Maldives. This species is readily distinguishable from the other Indo-West Pacific species of Polyonyx by the carapace and chelipeds covered with numerous transverse and oblique striae on the dorsal surface and the meri of the chelipeds having a very large, broadly rounded lobe on the dorsoflexor margin. The present record of P. utinomii from the Maldives is the first report outside Japan and greatly extends its geographical distribution westwards into the Indian Ocean.