Pseudopetalophthalmus japonicus, New Genus, New Species (Mysidacea: Petalophthalmidae)

Abstract

A new genus, Pseudopetalophthalmus, is established for P. japonicus, new species, collected from Japanese waters. Pseudopetalophthalmus is closely related to the genus Petalophthalmus, but distinguished from it by the rostrum lacking an acute process, the antennal scale armed with a single spine at the distal end of the naked part of the outer margin, the mandibular palp with the third segment 0.25 as long as the second segment and bearing 7 spines, the maxilla with a short exopod and an expanded distal lobe, and the telson with a truncate apex with spines arranged in definite series of 9 groups. The generic diagnosis of Petalophthalmus is amended to include Petalophthalmus australis. The genus Petalophthalmus was established by Willemoes-Suhm in 1875 for male specimens of P. armiger, collected in the tropical mid-Atlantic during the Challenger Expedition. The genus is easily recognizable by the powerful, long, prehensile mandibular palp, and the leaflike form of the eye, without visual elements (Tattersall, 1968). Later, Illig (1906) described a second species of the genus, P. oculatus, with well-developed eyes. With the establishment of P. caribbeanus by 0. S. Tattersall (1968), the initial diagnosis of the genus was completed. Finally, Panampunnayil (1982) revised the definition of Petalophthalmus for the reception of his new species, P. australis, based on: (1) the broad antennal scale with straight naked outer margin; (2) the shorter terminal segment of the mandibular palp, with only seven spines; (3) the considerably expanded lobe of the third segment of the maxilla; and (4) the telson with a small number of lateral spines, and the truncate apex with spines arranged in a definite series. The most recent species, P. macrops, was described by Tchindonova and Vereschchaka in 1991. A comparison of the five known species of Petalophthalmus with the material in the present work permits us to reestablish the diagnosis of the genus previous to the description of P. australis, and to establish a new genus and new species, Pseudopetalophthalmusjaponicus. The type specimens are deposited in the National Science Museum, Tokyo (NSMT), Japan.