Pliopagurus, Komai, 2013

Komai, Tomoyuki, 2013, A New Genus and New Species of Paguridae (Crustacea: Decapoda: Anomura) from the Bohol Sea, the Philippines, Species Diversity 18 (1), pp. 23-32 : 23-24

Pliopagurus gen. nov.

Type species. Pliopagurus curvimanus sp. nov. by present designation.

Diagnosis. Gills biserial, 11 pairs. Shield with lateral projections moderately separated from rostrum. Ocular acicles triangular, without submarginal spine; separated basally by more than basal width of 1 acicle. Maxillule with external lobe of endopod well-developed, never recurved, internal lobe with 2 bristle-like setae. Maxilla with posterior lobe of scaphognathite moderately broad. First maxilliped with slender endopod. Third maxilliped with welldeveloped crista dentata and prominent accessory tooth on ischium; merus and merus unarmed on dorsodistal margin. Right cheliped markedly longer larger than left; chela suboperculiform, with dorsomesial margin delimited by row of small spines; angle of articulation of chela and carpus about 30°. Left cheliped with chela not particularly compressed dorsoventrally, fingers not particularly excavated ventrally; angle of articulation of chela and carpus about 45°. Ambulatory legs with dorsodistal spine on each carpus. Fourth pereopods with well-developed dactyli, without preungual process; propodal rasp consisting of single row of corneous scales. Third thoracic sternite with trace of median notch, unarmed; sixth thoracic sternite with subtrapezoidal anterior lobe; no capsulate setae on posterior sternites. Males with coxae of fifth pereopods symmetrical, each having very short, strongly tapering sexual tube; 3 (third to fifth) unpaired, unequally biramous left pleopods. Females with paired gonopores on coxae of third pereopods; pleon with paired first pleopods incompletely 2-segmented and modified as gonopods, and with 4 unpaired (second to fifth) left pleopods, second to fourth with both rami well-developed, fifth with endopod reduced. Pleon dextrally twisted. Uropods strongly asymmetrical; protopods not strongly produced posteriorly. Telson with faint or shallow lateral indentations; posterior lobes slightly asymmetrical, terminal margins strongly oblique, each with row of minute spinules; posterolateral margins without corneous or calcareous plate.

Remarks. In her initial revision of the “ Pylopagurus -Tomopagurus ” group, McLaughlin (1981a) subdivided Pylopagurus A. Milne-Edwards and Bouvier, 1891 into 11 genera [ Agaricochirus McLaughlin, 1981 , Anisopagurus McLaughlin, 1981 , Australeremus McLaughlin, 1981, Enallopaguropsis McLaughlin, 1981 , Enallopagurus McLaughlin, 1981 , Haigia McLaughlin, 1981 (renamed Haigiopagurus McLaughlin, 2005 because of homonymy; see McLaughlin 2005), Lophopagurus McLaughlin, 1981 , Manucomplanus McLaughlin, 1981 , Phimochirus McLaughlin, 1981 , Pylopagurus sensu stricto, and Rhodochirus McLaughlin, 1981 ] and rediagnosed Tomopagurus to include species in which female first pleopods might not develop. Lemaitre and McLaughlin (1996) subsequently described a new genus, Protoniopagurus Lemaitre and McLaughlin, 1996 , and added it to the “ Pylopagurus - Tomopagurus ” group. De Saint Laurent and McLaughlin (2000) reduced Australeremus to a subgenus of Lophopagurus , because they considered that Eupagurus kirkii Filhol, 1883 links morphological extremes in the two generic taxa. McLaughlin and Lemaitre (2001) rediagnosed Pylopagurus and further described and added one new genus, Pylopaguridium McLaughlin and Lemaitre, 2001 , to the “ Pylopagurus - Tomopagurus ” group. Prior to McLaughlin and Lemaitre (2001), the development of any form of male secondary sexual characters (e.g., the development of sexual tubes) had not been recognized in this group of genera, but McLaughlin and Lemaitre (2001) found that two species of Pylopagurus [ P. discoidalis (A. Milne-Edwards, 1880) and P. macgeorgei McLaughlin and Lemaitre, 2001 ] could have short sexual tube(s) on one or both gonopores of the coxae of the fifth pereopods in males. Lemaitre and McLaughlin (2003a) further noticed that species of Agaricochirus , Enallopaguropsis , and Enallopagurus could occasionally have vasa deferentia produced to form short, tubular papillae.

The present new species is linked to the 13 genera of the “ Pylopagurus - Tomopagurus ” group by the possession of 11 pairs of biserial gills and the presence of paired first female pleopods modified as gonopods. In the general morphology of the shield and chelipeds, Pliopagurus gen. nov. appears closest to Lophopagurus , but the structure of the left chela of the new genus is characteristic in the lack of a median elevation on the dorsal surface and in having a rounded dorsolateral or lateral surface. In all known species currently assigned to Lophopagurus , the left chela has a dorsomedian crest and/or a keeled and spinose lateral margin ( McLaughlin and Gunn 1994; de Saint Laurent and McLaughlin 2000). Furthermore, the smooth dorsal surface of the right chela and the presence of “very short” [following the protocol proposed by McLaughlin (2003)] but prominent, abruptly tapering sexual tubes on the coxae of the fifth pereopods in males distinguish the new genus from Lophopagurus . There are no species of Lophopagurus with sexual tubes or protrusions of the vasa deferentia. The dorsal surface of the right chela is usually armed with numerous spines or tubercles in species assigned to Lophopagurus .

Following the key of genera of the “ Pylopagurus - Tomopagurus ” group by Lemaitre and McLaughlin (2003a), the present new genus is placed close to Tomopagurus and Haigiopagurus (as Haigia ). Nevertheless, species of Tomopagurus all have a non-suboperculiform, strongly spinose or tuberculate right chela and a spinose or tuberculate left chela, with fingers ventrally forming a spoon-like excavation when closed ( McLaughlin 1981a; Lemaitre and McLaughlin 2003a). In contrast, in Pliopagurus gen. nov., the right chela is suboperculiform, the dorsal surfaces of both chelae are almost unarmed except for spines or tubercles on the dorsolateral and/or dorsomesial margins, and the fingers of the left chela are not distinctly excavated ventrally, thus not forming a spoon-like structure. As for Haigiopagurus , the lateral margin of the left chela is noticeably expanded into a keel that bears a row of strong spines ( McLaughlin and Lemaitre 2001). Finally, in Haigiopagurus , development of sexual tubes in males is not seen and both chelae have numerous tufts of short stiff setae ( McLaughlin and Lemaitre 2001).

Without examination of the female, the present new species might be easily misidentified as a species of Anapagrides de Saint Laurent-Dechancé, 1966 . In particular, superficial similarity between Pliopagurus curvimanus sp. nov. and A. aequalis Komai, 1999 is substantial in the general shape and armature of the right cheliped and the possession of very short sexual tubes on both coxae of the fifth pereopods in males, although the new species is readily distinguished from the latter by the lack of a dorsomedian crest on the palm of the left cheliped (cf. Komai 1999).

Other genera characterized by the combination of the possession of 11 pairs of biserial gills, the presence of paired first pleopods in females, and the development of male sexual tube(s) include Cycetopagurus McLaughlin, 2004 and Nematopagurus A. Milne-Edwards and Bouvier, 1892 . These two genera are primarily differentiated from Pliopagurus gen. nov. by the possession of a long right sexual tube with a filiform distal part and subequal chelipeds (cf. McLaughlin 2004 a, 2004b). Goreopagurus McLaughlin, 1988 was also originally diagnosed by the same combination of characters, but the subsequent discovery of G. poorei Lemaitre and McLaughlin, 2003 , which is characterized by 11 pairs of distally quadriserial gills and the lack of male sexual tubes, led Lemaitre and McLaughlin (2003b) to emend the diagnosis of the genus. Goreopagurus is easily distinguished from the present new genus by an unusual, sexually dimorphic expansion of the carpus of the right cheliped ( Lemaitre and McLaughlin 2003b).

Etymology. From the Greek prefix “ plio -”, derived from pleion (=more), and the generic name Pagurus , alluding to the discovery of one additional new genus closely related to the “ Pylopagurus - Tomopagurus ” group of McLaughlin (1981a).