Geosesarma lawrencei, Manuel-Santos, Marivene R. & Yeo, Darren C. J., 2007

Manuel-Santos, Marivene R. & Yeo, Darren C. J., 2007, A new species of Geosesarma from Palawan, Philippines (Crustacea: Decapoda: Brachyura: Sesarmidae), Zootaxa 1607, pp. 63-67 : 63-67

Geosesarma lawrencei , new species

( Figs. 1 , 2 )

Material examined. Holotype, male (10.3 x 9.7 mm) ( NMCR 27023), Sitio Kamantian, Barangay Samarinana [=Samareñana], Brooke’s Point, Palawan, Philippine Islands. 550 m asl, coll. L. Liao, Dec.2001. Paratypes: Male (9.5 by 8.6 mm) ( ZRC 2007.0121), female (9.9 by 9.5 mm) ( NMCR 28011), same data as holotype.

Diagnosis. Carapace squarish, very slightly broader than long, anterior dorsal carapace and anterolateral regions covered with groups of small sharp granules. Frontal margin strongly sinuous, bilobed, subequal to half carapace width. Postfrontal cristae distinctly separated by deep median groove, each crista bilobed with each lobe separated by shallow groove. External orbital angle acutely triangular, directed obliquely outwards, separated from first epibranchial tooth by broad, shallow but distinct V-shaped cleft. Lateral margin slightly convex posteriorly. Exopod of third maxilliped not reaching midlength of merus, with numerous long setae distally, with well-developed flagellum exceeding width of merus. Ambulatory legs relatively long, slender. Male abdomen triangular; lateral margins of fifth and sixth segments convex. G1 slender, almost straight; distal part short, less than 0.2 times length of proximal part, bent very slightly outwards, tip rounded; proximal part with upper inner margin gently convex, outer margin gently undulating.

Description of holotype. Carapace squarish, very slightly broader than long, dorsal surface covered with small sharp granules in groups of two or three; regions distinctly demarcated, with relatively deep grooves; median gastric groove deep, H-shaped; anterior grooves shallow; transverse groove separating cardiac and intestinal regions distinct ( Fig. 1 A). Frontal margin strongly deflexed, strongly sinuous, bilobed, subcristate ( Fig. 1 A–C). Postfrontal cristae distinct, sharp, separated by deep median groove, each crista bilobed, each lobe separated by shallow groove; surface of frontal region vertically concave ( Fig. 1 A, B). External orbital angle acutely triangular, directed obliquely outwards, separated from first epibranchial tooth by broad, shallow but distinct V-shaped cleft; first epibranchial tooth smaller than external orbital angle, triangular with very shallow posterior notch delineating it from lateral margin; second epibranchial tooth separated from the first epibranchial tooth by very shallow notch, third indistinct ( Fig. 1 A). Lateral margin slightly convex posteriorly; posterolateral regions with low oblique striae ( Fig. 1 A). Eyes large, reaching the tip of external orbital angle ( Fig. 1 A–C).

Merus of third maxilliped round, with median portion of lateral margin produced as slight, blunt angle, about two times greater than proximal margin width, with strong median oblique ridge; ischium with shallow median sulcus, outer ridge distinct; exopod slender, not reaching midlength of merus, with numerous long setae distally, with well-developed flagellum exceeding width of merus ( Fig. 1 B, C, 2C).

Chelipeds subequal; outer surface of palm spinulose, covered with low, scattered spinules especially on upper and lower margins; fingers subequal to length of palm, proximal part of upper margin of dactylus of left chela lined with 12 low, anteriorly-directed granules (10 granules on right chela of dactylus), cutting edge lined with numerous teeth and denticles, distal part of finger pectinated to form blade-like cutting edges; inner margin of carpus gently serrated, inner distal spine weak but distinct, with scattered low granules on dorsal surface; outer surface of merus slightly rugose, inner surface smooth, with serrated inner margin, without subdistal spine ( Fig. 1 A–C).

Ambulatory legs long, slender; third pair longest; merus broad, with low, truncated subdistal dorsal tooth, upper margin very gently serrated; propodus slender; dactylus shorter than propodus, straight, gently curved distally; segments lined with numerous short, stiff spiniform hairs. Abdomen triangular, lined with numerous short setae; seventh segment with rounded tip, longer than sixth, lateral margins of sixth and seventh segments convex ( Fig. 1 A, C).

G1 slender, almost straight; distal part bent very slightly outwards, pectinated, straight then gently tapering to a rounded tip, tube-like with distal opening on dorsal side, laterally flattened towards ventral side; proximal part with upper inner margin gently convex; outer margin gently undulating, distally with numerous setae ( Fig. 2 A, B). G2 very short, less than 0.3 times length of G1, lacking flagellum, expanded proximally, tapered distally, curved, with distal part directed outwards ( Fig. 2 D).

Paratypes. The paratype male is slightly smaller than the holotype but agrees with it in all major aspects. The paratype female is similar to the male holotype except for the external reproductive structures.

Etymology. The species is named after its collector, Dr. Lawrence Liao, whose interests extend far beyond his love and dedication for his work as a phycologist. He is also an avid field collector who has contributed a wealth of new discoveries to the fauna of the Philippines, including crabs.

Remarks. The slender G1 of Geosesarma lawrencei , new species, is similar to that of G. rathbunae from Panay Island, which is also the geographically closest Philippine congener. However, G. l a w re n c e i is easily distinguished from G. rathbunae by the following characters: frontal margin strongly sinuous, distinctly bilobed when viewed dorsally (versus frontal margin gently sinuous, weakly bilobed when viewed dorsally); frontal margin subequal in length to half carapace width resulting in eyes appearing closer together (versus frontal margin longer than half carapace width, eyes appearing further apart); postfrontal cristae distinctly separated by deep median groove, with each crista bilobed and each lobe being separated by shallow groove (versus postfrontal cristae weakly separated by shallow median groove, each crista with undulating margin, not appearing bilobed); cleft separating external orbital angle from first epibranchial tooth comparatively broad and shallow (versus cleft narrower and deeper); carapace lateral margins slightly convex posteriorly (versus lateral margins straight); ambulatory legs comparatively long and slender (versus ambulatory legs shorter and stouter); G1 almost straight with distal part bent very slightly outwards, with a rounded tip (versus G1 with distal part bent obliquely outwards at approximately 30 degrees to the long axis, with a sharp tip); G1 outer margin gently undulating (versus outer margin straight); pectinated distal part of G1 proportionally shorter, about 0.17 times of proximal part (versus pectinated distal part proportionally longer, about 0.36 times of proximal part); and G1 proximal part with upper inner margin gently convex (versus proximal part upper inner margin distinctly convex, appearing hump-like) ( Figs. 1 A–C, 2A, B; cf. Serène 1968: Figs 5, 6, Pl. 1 fig. 4).

Geosesarma lawrencei can be distinguished from G. protos by the squarish carapace (versus trapezoidal carapace); the well-developed flagellum on the exopod of the third maxilliped (versus third maxilliped lacking a flagellum on the exopod); and the slender G1 (versus stout G1) ( Figs. 1 A, 2A–C; cf. Ng & Takeda 1992: Figs. 1 A, B, G–J).

There is currently some doubt over Serène and Soh’s (1970) generic placement of Geosesarma vicentese due to its unusual morphology (Ng & Takeda 1992). In any case, G. vicentese is least likely among the Philippine species to be confused with G. lawrencei as the new species differs considerably from the former in the anterior portions of the carapace and anterolateral regions being covered with sharp granules (versus flattened granules); the postfrontal cristae being strongly separated by distinct deep grooves (versus postfrontal cristae weakly separated by gentle, shallow grooves); and the lateral margins of the fifth and sixth male abdominal segments being convex (versus concave) ( Figs. 1 A–C; cf. Rathbun 1914; Ng & Takeda 1992).

In addition to the known species of Geosesarma from the Philippines, two other congeners, G. sabanus Ng, 1995 a, and G. a u r a n t i u m Ng, 1995b, both from Sabah in northern Borneo, warrant comparison by virtue of the proximity of their type localities to Palawan. Both species, however, are clearly differentiated from G. lawrencei by the absence of a flagellum on the third maxilliped and by the stout and distally bent form of their G1 (versus flagellum present on third maxilliped and slender and almost straight G1) ( Fig. 2 A–C; cf. Ng 1995a: Figs. 1 B, E–G, 1995b: Figs. 1 G, 2).

Distribution. Palawan, Philippines.

Figures

FIGURE 1. Geosesarma lawrencei, new species. Holotype, male (10.3 by 9.7 mm) (NMCR 27023). A, dorsal view; B, frontal view; C, ventral view.

FIGURE 2. Geosesarma lawrencei, new species. Holotype, male (10.3 by 9.7 mm) (NMCR 27023). A, ventral view of left G 1; B, dorsal view of left G 1; C, left third maxilliped; D, left G 2. Scales: 1.0 mm in A – C; 0.5 mm in D.