Parasesarma dumacense ( Rathbun, 1914 )

Rahayu, Dwi Listyo & Ng, Peter K. L., 2010, Revision of the Parasesarma plicatum (Latreille, 1803) species-group (Crustacea: Decapoda: Brachyura: Sesarmidae), Zootaxa 2327, pp. 1-22 : 15-20

Parasesarma dumacense ( Rathbun, 1914)

( Figs. 11–14 )

Sesarma (Parasesarma) dumacense Rathbun, 1914: 80 . Parasesarma dumacense — Ng et al. 2008: 222.

Type. Sesarma (Parasesarma) dumacense Rathbun, 1914 , holotype female (17.6 x 13.2 mm) ( USNM 45922), Dumaca River, Luzon, Philippines.

Material examined. 4 males (18.7 x 15; 19.2 x 15.5; 20.9 x 16.8; 21.0 x 17.6 mm), 2 females (18.0 x 14.0 mm, 15.6 x 11.2 mm) ( ZRC 2008.0833), 5 males (19.0 x 17.3 mm; 18.7 x 16.8 mm; 16.3 x 15.0 mm; 13.3 x 11.7 mm; 11.3 x 10.1 mm), 4 ovigerous females (16.4 x 14.3 mm; 15.4 x 13.2 mm; 13.4 x 11.5 mm; 13.3 x 11.3 mm), 1 female (10.0 x 8.7 mm) ( TMCD), 5 males (19.3 x 17.4 mm; 17.4 x 15.8 mm; 14.6 x 13.3 mm; 13.4 x 11.8 mm; 12.4 x 10.9 mm), 2 females (14.8 x 13.0 mm; 14.7 x 12.4 mm), 3 ovigerous females (14.7 x 12.4 mm, 13.9 x 11.3 mm, 13.1 x 11.3 mm) ( ASIZ), Kawasan Fall, Matutinao, Cebu, Philippines, coll. H.-C. Liu et al., 25 November 2001.

Diagnosis. Carapace 1.25 times broader than long ( Figs. 11 A, 12A, B, 13A); mesogastric, cardiac regions well defined, intestinal region moderately defined; lateral carapace surface lined with oblique striae; carapace surface with sparsely scattered tufts of setae, lateral margins with short setae. Postfrontal margin with 4 distinct, similar lobes, separated by narrow grooves. Front deflexed downward, margin bilobed from dorsal view, each lobe broadly convex, separated by broad, shallow median concavity. External orbital tooth triangular, directed upward, fused with entire lateral carapace margin; greatest width of carapace just behind external orbital tooth. Eyes not extending beyond edge of external orbital tooth.

Chelipeds subequal ( Figs. 12 C, 13E), large, robust. Merus with posterior border carinate, minutely tuberculate, with subdistal spine; anterior border carinate ending in large subdistal spine; outer surface striated, inner surface with longitudinal row of setae, sparse setae near posterior border. Carpus with inner angle not produced, outer margin, striated across dorsal surface. Upper surface of palm with 2 transverse pectinated crests ( Fig. 13 D). Primary crest with 13 or 14 broad teeth. Secondary crest well developed, slightly shorter than primary, with 8–10, broader teeth. Outer surface of palm striated proximally, granular distally, naked; inner surface of palm with several tubercles. Fixed finger rounded, smooth to gently granular on outer surface, longitudinal ridge medially. Dorsal surface of dactylus with 8 tubercles, small proximally, becoming larger, lower distally; all tubercles distinct, subcircular, each tubercle with fine transverse lines, faint transverse ridge on tip. Several prominent tubercles on proximal third of inner edge of dorsal surface. Fingers with chitinous tips, crossing at tip when closed.

Walking legs flattened, relatively robust, broad ( Figs 12 A, B, 13A); second, third pairs sub-equal, longer than others, about 1.5 times carapace width. Merus of third leg 1.8 times as long as wide; anterior margin of merus with acute subdistal spine. Meri of legs 1–3 with transverse striae on upper surface, merus of leg 4 smooth. Carpus with 2 accessory carinae on outer surface. Propodi of legs 1–3 2.5 times as long as wide, short stiff brush-like setae along dorsal margin, ventral margins with short brush-like setae on distal third followed by several long chitinous setae. Dactylus almost same length as propodus, slightly recurved, terminating in acute calcareous tip, dorsal margin with several prominent long stiff setae, ventral margin with short brushlike setae in proximal third.

Male abdomen relatively broad ( Figs. 13 B, 14E). Telson semicircular, evenly rounded, very slightly longer than somite 6; somite 6 almost twice, half as long as wide, lateral margins slightly convex. Somites 3– 5 progressively more trapezoidal, lateral margins of somites 4, 5 straight, lateral margins of somite 3 slightly convex, somites 1, 2 very narrow longitudinally.

G1 stout ( Figs. 14 A–D), straight; apical process gently bent to form 45º angle, produced, corneous part short, wide, with rounded tip. Setae long, simple, originating at base of apical process. G2 very short.

Colour. The carapace of small specimens have distinct patches of light and dark colours ( Fig. 12 B), while larger ones have less distinct patterns ( Fig. 12 A). The chelae of adults are orange ( Fig. 12 C). The blotchy carapace pattern and uniformly orange chelae easily distinguish P. dumacense from other members of the species-group.

Remarks. Described on the basis of a single female from Dumaca River in Luzon, Philippines ( Fig. 11 ) and never reported again, Parasesarma dumacense is a poorly known species. Rathbun (1914) noted in the description that it was allied to P. plicatum but differed in the form of its lateral margins, of the external orbital tooth, of the frontal margin, more slender cheliped propodus, position of the oblique pectinated crest on the dorsal surface of the chela, and the structure of the ambulatory meri. The present specimens from Cebu in the central Philippines agree well with the original description of P. dumacense and is thus referred to this species. The colour pattern described by Rathbun (1914: 81) (“carapace is blotched, and the legs finely mottled, with dark on light ground”) agree well with that of the present specimens ( Fig. 12 A, B), although she did not indicate the colour of the chelae.

Comparisons with specimens of P. affine from Taiwan and Japan indicate that the two taxa are very close, but can nevertheless still be confidently separated by their differently shaped G1s, with that of P. dumacense relatively stouter and the distal pectinated part shorter and broader ( Fig. 14 A-D) than that of P. affine ( Fig. 7 A-D). The tubercles of the male dactylus of P. a f f i n e are also very different in form to those of P. dumacense , being relatively symmetrical, prominent and with a narrow, transversely subovate median flattened ridge marking its highest point. In P. dumacense , the dactylar tubercles are also relatively symmetrical but very low, almost flattened, with the highest point marked by a narrower flattened ridge.

Geographical distribution. Philippines.

Figures

FIGURE 7. Parasesarma affine (De Haan, 1837). Lectotype male (19.4 x 14.9 mm) (RMNH 129), Japan. A – D, right G 1; E, abdomen. A, B, scales = 1 mm; C, D, scales = 0.5 mm; E, scale = 5 mm.

FIGURE 11. Parasesarma dumacense (Rathbun, 1914). Female holotype (19.0 x 14.0 mm) (USNM 45922), Philippines. A, overall dorsal view; B, abdomen; C, frontal view of carapace

FIGURE 12. Parasesarma dumacense (Rathbun, 1914). Colour in life, male (18.7 x 15.0 mm) (ZRC 2008.0833), Philippines. A, B, overall dorsal view; C, left cheliped.

FIGURE 13. Parasesarma dumacense (Rathbun, 1914). Male (21 x 17.6 mm) (ZRC 2008.0833), Philippines, A, overall dorsal view; B, frontal view of carapace; C, ventral view showing anterior part of thoracic sternum, abdomen; D, dorsal surface of dactylus of left cheliped showing dactylar tubercles; E, left cheliped.

FIGURE 14. Parasesarma dumacense (Rathbun, 1914). Male (21.0 x 17.6 mm) (ZRC 2008.0833), Philippines. A – D, right G 1; E, abdomen. Scales = 1 mm.