Plesiomenaeus, Bruce, 2009

Bruce, A. J., 2009, Plesiomenaeus poorei gen. nov., sp nov., (Crustacea: Decapoda: Pontoniinae) from Zanzibar, Memoirs of Museum Victoria 66 (1), pp. 25-34 : 25

Plesiomenaeus gen. nov.

Diagnosis Rostrum greatly reduced, compressed, uni-dentate, carapace without supraorbital, epigastric, hepatic or antennal spines, inferior orbital angle acute, first abdominal tergite without anteromedian lobe, pleura rounded, telson with two pairs of small dorsal spines, three pairs of posterior marginal spines, scaphocerite reduced, labrum normal, mandible without palp, maxillipeds with flagella slender, with four long, plumose terminal setae, maxilla with basal endite simple, third maxilliped with ischiomerus and basis fused, coxa without arthrobranch, fourth thoracic sternite without median process, first pereiopod chela with fingers subspatulate, cutting edges entire, dactyl with tridentate tip, medial and lateral teeth denticulate, fixed finger distally bidentate, second pereiopods well developed, unequal, similar, major dactyl fingers simple, without molar process and fossa, minor fingers non-shearing, ambulatory pereiopods robust, third propod most slender, fifth propod stoutest, dactyls simply biunguiculate, uropodal propod unarmed, exopod of uropod with distolateral tooth and spine.

Type species. Plesiomenaeus poorei sp. nov., by present selection and monotypy.

Etymology. From plesios (Greek) near, and part of the name Periclimenaeus , first used by Borradaile (1915), as the shrimp was initially identified as a strange Periclimenaeus . Gender masculine.

Systematic position. The genus Plesiomenaeus most closely resembles the genus Periclimenaeus Borradaile1915 , type species Periclimenaeus robustus Borradaile, 1915 (redescribed by Bruce, 2005). In this species a marked thickening of the posterior three fifths of the second pereiopod dactylar cutting edge is distinctly demarcated from the swollen base of the dactyl ( Bruce, 2005, fig. 2C). This thickened portion is less developed than in several other species of the genus where it forms the typical posteriorly and anteriorly demarcated molar tooth, with a large well delineated opposing socket on the fixed finger.In P.robustus , and other species of Periclimenaeus , the occlusal surface of this thickened portion is distinctly flattened. In Periclimenaeus , and many other pontoniine genera, the proximal occlusal end of the dactyl is normally swollen and quite distinct from the molar process which is developed on the intermediate portion of the cutting edge (see fig, 4J, Periclimeaeus gorgonidarum (Balss) , Wilson Island, Queensland, 6.0 m, coll. N.L. Bruce, 28 August 1980, AJB 3106, QM W28914). In contrast, in Plesiomenaeus there is no trace of a molar process in this position. The proximal dactyl is swollen and articulates in a deep longitudinal depression in the proximal fixed finger but this lacks a defined anterior margin and does not form a socket. In Plesiomenaeus the second pereiopod chelae are similar but differing in size, in contrast in Periclimenaeus they are of different morphology. Plesiomenaeus also lacks the anteromedian lobe on the dorsal margin of the first abdominal tergite conspicuous in P. robustus .