Michaelimenes, Okuno, 2017

Michaelimenes View in CoL n. gen.

Type species. Periclimenes perlucidus Bruce, 1969 ; by present designation.

Etymology. The present new genus is named in honor of the late Dr. Michael Türkay (1948–2015) for his great contributions to the systematics of various groups of decapod crustaceans from all over the world, combined with part of Periclimenes . Gender:masculine.

Diagnosis. Small sized palaemonid shrimp with subcylindrical, slender body form. Carapace smooth, glabrous, antennal and fixed hepatic spines present, orbit feebly developed, inferior orbital angle produced, without reflected inner ventral flange, pterygostomial margin rounded, feebly produced. Rostrum well developed, horizontal, ventral margin straight, dorsally and ventrally dentate, lateral carina obsolete. Ophthalmic somite without interocular beak. Fourth thoracic sternite without acute median process. Abdomen smooth, third tergite non-carinate or posteriorly produced, pleura of fourth and fifth segments posteroventrally produced, rounded. Telson slightly longer than sixth abdominal somite, gradually tapering distally, with two pairs of dorsolateral spines, posterior margin with three pairs of spines. Eyes with well developed globular cornea. Antennule normally developed.Antenna with basicerite armed distolaterally with a single acute tooth, without dorsal angular process, scaphocerite well developed.Epistome without horn-like process. Mandible without palp, molar and incisor processes normal. Maxillula with bilobed palp, upper and lower laciniae well developed. Maxilla with normal palp, distal endite bifid, proximal endite feebly produced, scaphognathite broad. Maxillipeds with slender exopodal flagella. First maxilliped with caridean lobe large, epipod triangular. Second maxilliped with epipod oval, without podobranch. Third maxilliped with coxal plate large, subquadrate; arthrobranch small. First pereiopod slender, with dactylus normal, not subspatulate, fingers with cutting edges unarmed. Second pereiopods smooth, glabrous, equal or unequal in length and shape. Major second pereiopod with carpus short, slightly widended distally; palm elongate, subcylindrical, entire; fixed finger with proximal excavation on the cutting surface, for the reception of proximal part of dactylar cutting edge when both fingers closed, dactylus short, dorsally with developed flange, cutting edge dentate proximally. Minor second pereiopod with carpus short or elongate; palm subcylindrical, entire; fixed finger with proximal excavation similar to major pereiopod, dorsomesial flange of dactylus distinct or obsolete. Ambulatory pereiopods slender, meri unarmed, propodi armed with ventral spines, but without transverse rows of tufts of dense setae, dactyli with distoventral tooth on corpus small or lacking. Male first pleopod with endopod distally rounded, mesially with slender or angular process. Male second pleopod with endopod with appendix interna longer than appendix masculina.

Species included. Periclimenes latipollex Kemp, 1922 , Periclimenes perlucidus Bruce, 1969 (type species) and Periclimenes platydactylus Li, 2008 .

Common name. Yaiba-kakure-ebi zoku (new standard Japanese name).

Remarks. Michaelimenes is discriminated from other allied genera by the combination of having the fingers of the first pereiopod unarmed and non-subspatulate ( Fig. 1A View Figure 1 ), the second pereiopod with a smooth palm, a proximal excavation on the cutting surface of the fixed finger ( Fig. 1B, E View Figure 1 ) and a dorsal flange on the dactylus ( Fig. 1C, D View Figure 1 ), the straight and horizontal rostrum dorsally and ventrally dentate ( Fig. 3A View Figure 3 ), and the feebly developed orbit ( Fig. 3A View Figure 3 ). It is noteworthy that the proximal excavation on the second pereiopodal fixed finger assumes the reception to the dactylar proximal cutting edge when the fingers closed ( Fig. 1D View Figure 1 ), therefore, the dactylus and fixed finger slide against each other along both proximal cutting edges. In most of shrimps belonging to the genus Periclimenes and its related genera, the cutting edges coincide each other. Furthermore, the distal edge of the fixed finger fits in the oblique mesial surface ventrad to the dorsal flange of the dactylus and thus, the gape does not occur between the completely closed fingers. This unusual structure distinguishes Michaelimenes from the genus Periclimenes , as typified by its type species, P. amethysteus (Risso, 1826) (see Grippa and Udekem d’Acoz, 1996), and other congeneric species as generic rank except for P. latipollex and P. platydactylus .

Periclimenes latipollex View in CoL was originally described by Kemp (1922) on the basis of three specimens from the Mergui Archipelago, eastern Indian Ocean. It has been additionally recorded from the depths of 73–440 m at Somalia, Kenya, Philippines, Indonesia, New Caledonia and Japan ( Hayashi, 2005; Li and Bruce, 2006). Kemp (1922) mentioned that the positional relation between the dactylus and fixed finger of the second pereiopod in P. latipollex View in CoL resembles that of the blades of scissors, and Bruce (1991) illustrated this structure. Since this diagnostic character links P. latipollex View in CoL with M. perlucidus View in CoL , this species should also be considered as a member of Michaelimenes View in CoL .

Li (2008) originally described P. platydactylus View in CoL on the basis of the single ovigerous female holotype from a depth of 108–112 m at the Marquesas Islands in French Polynesia. At that time, P. platydactylus View in CoL was compared with the Periclimenes alcocki Kemp, 1922 View in CoL species group (now considered as the separate genus under the name of Bathymenes Kou, Li and Bruce, 2016 View in CoL ). The similarity between P. platydactylus View in CoL and P. perlucidus View in CoL was not alluded to the original description, although these two species share the flange on the dactylus and proximal excavation on the fixed fineger of the second pereiopod. Herein, I regard the two species as congeneric, and place P. platydactylus View in CoL into Michaelimenes View in CoL .

In general morphology, P.latipollex , P.perlucidus and P. platydactylus also share the straight and horizontal rostrum with both margins dentate, and the feebly