Parasesarma ungulatum (H. Milne Edwards, 1853 )

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 : 11-15

Parasesarma ungulatum (H. Milne Edwards, 1853)

( Figs. 8–10 )

Sesarma ungulata H. Milne Edwards, 1853: 184 .

Sesarma quadrata — A. Milne-Edwards 1873: 302.

Sesarma quadrata — Thallwitz 1892: 37. – De Man 1892: 328. – Lanchester 1900: 257. – Schenkel 1902: 549. Sesarma (Parasesarma) quadrata — Lanchester 1902: 550.

Sesarma (Parasesarma) quadrata var. affinis — De Man 1902: 533.

Sesarma (Parasesarma) plicatum — Rathbun 1907: 34. – Rathbun 1910: 309.

Types. Sesarma ungulata H. Milne Edwards, 1853: 184 , 1 dried lectotype male (12.1 x 8.4 mm) (MNHN BP 3694), Sulawesi.

Material examined. 2 males (21.4 x 15.2 mm, 15.2 x 11.3 mm), 1 female (15.3 x 12.7mm) ( ZRC 1998.336), salt marsh and mangrove patches, immediately downstream of Tai Tam Dam, south coast, Tai Tam, Hong Kong, coll. P. K. L. Ng, 6 June 1996. – 1 male (18.3 x 14.7 mm), 1 female (19.1 x 14.8 mm) ( ZRC 1998.334-335), Hainan Island, China, coll. Y. Z. Song, 25 July 1957. – 6 males (14.3 x 10.9 – 19.5 x 15.4 mm), 2 females (16.0 x 12.4 mm, 19.4 x 15.4 mm), 2 ovigerous females (18.6 x 15.1 mm, 14.7 x 11.3 mm) ( ZRC 1999.566), Chonburi mangroves, Gulf of Thailand, Thailand, coll. P. K. L. Ng, 29 September 1998. – 1 male (21.2 by 16.7 mm) ( ZRC 1967.11.9.3), 1 ovigerous female (17.6 x 13.6 mm) ( ZRC 1967.11.9.4), near Banghen, Thailand, coll. R. Serène, 11 January 1965. – 5 males (12.4 x 9.6 – 16.8 x 12.5 mm), 4 ovigerous females (13.2 x 10.2 – 17.9 x 13.9 mm) ( ZRC 1965.7.29.192-201), Kuantan, Pahang, Malaysia, September 1935. – 57 males (8.4 x 6.6 mm – 18.0 x 14.5 mm), 37 females (8.4 x 6.4 – 15.6x 12.2 mm), 14 ovigerous females (11.4 x 8.9 –15.2 x 11.5) ( ZRC 1973.12.2.389-488), Kuantan, Pahang, Malaysia, September 1935. – 1 male (17.3 x 13.9 mm), 6 females (10.1 x 7.8 – 17.2 x 13.4 mm), 2 ovigerous females (13.1 x 10.1mm, 13.5 x 10.6 mm) ( ZRC 2000.1646), Tanjung Aru, Sabah, Kota Kinabalu, Malaysia, coll. C. D. Schubart, 23 June 2000. – 7 males (7.3 x 5.4 – 13.8 x 10.7 mm), 1 female (14.2 x 11.0 mm) ( ZRC 2000.1659), Sabah, Kota Kinabalu, Malaysia, coll. P. K. L. Ng & C. D. Schubart, 22 June 2000. – 1 male (9.3 x 7.5 mm) ( ZRC 1965.7.29.204), Kuala Sedili, Johor, Malaysia, 25 Nov 1934. – 1 male (18 x 14.4 mm), 1 ovigerous female (14.7 x 11.7 mm) ( ZRC 2008.0904), Pulau Bukom, Singapore, 3 October 1934. – 1 male (9.9 x 7.7 mm); 4 males (8.1 x 6.2 mm – 17.5 x 14.2 mm), 1 female (11.4 x 8.8 mm), 1 ovigerous female (16.3 x 12.6 mm) ( MZB Cru 1515), mangrove, Ajkwa River, Papua, Indonesia, coll. D. L. Rahayu, 10 October 2002. – 6 males (12.8 x 10 – 17.3 x 13.8 mm), 2 females (12.5 x 9.7 mm, 16 x 12.4 mm) ( ZRC 2008.0815), Ajkwa River, Papua, Indonesia, coll. D. L. Rahayu, 21 June 2008. – 2 males (16.9 x 13.7, 16.8 x 12.8 mm) ( ZRC), Teluk Kombal, Lombok, Indonesia, 7 April 2008.

Diagnosis. Carapace 1.25 broader than long ( Figs. 8 A, 9A); mesogastric, cardiac regions well defined, intestinal region moderately defined; lateral carapace surface lined with strong 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 downwards, 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. 8 B, 9E), 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, across dorsal surface striated. Upper surface of palm with 2 transverse pectinated crests ( Fig. 9 D). Primary crest composed of 15–17 broad teeth. Secondary crest well developed, slightly shorter than primary, with 8–14 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, low ridge medially; without ventral ridge, moderately long. Dorsal surface of dactylus with 10–12 tubercles ( Fig. 9 D), small proximally, becoming larger distally; all tubercles distinct, subcircular, each tubercle with fine transverse lines, transverse ridge on tip. Several low tubercles on proximal third of inner edge of dorsal surface. Fingers with tips chitinous, crossing when closed; adult males with moderately wide gape left when fingers closed.

Walking legs robust, flattened, broad ( Figs. 8 A, 9A); second, third pairs sub-equal, longer than others, about 1.5 times carapace width. Merus of third leg 2 times as long as wide; anterior margin of merus with an 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 2.8 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 brush-like setae in proximal third.

Male abdomen relatively broad ( Figs. 9 B, 10E). Telson semicircular, evenly rounded, very slightly longer than somite 6; somite 6 almost 2.5 times 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 ( Fig. 10 A–D), straight; apical process very gently bent to form 60º angle, produced, corneous part short, wide, with truncate tip. Setae long, simple, originating at base of apical process. G2 very short. Female with chelipeds smaller than male, pectinated crests on palm replaced by 2 traverse rows of tubercles, 10–12 dactylar tubercles, indistinct.

Colour. Carapace dark brown with transverse band of light brown on subfrontal region, cheliped and ambulatory legs orange-red ( Fig. 8 ). The dark carapace with a light frontal band and more uniformly red chelae easily distinguishes fresh specimens of P. ungulatum from other members of the species-group.

Remarks. De Man (1888: 169) first considered this species to be conspecific with Parasesarma affinis (de Haan, 1837) and Sesarma quadrata Fabricus 1898 (now Parasesarma plicatum Latreille, 1803 ), and that synonymy has been accepted until now.

Henri Milne Edwards (1853), in describing this species, did not indicate how many specimens he had, only that his material was from an unspecified location in Celebes (= Sulawesi). There is one dried specimen in MNHN which agrees with the brief description and is labelled as a type of S. ungulata . This specimen is here designated the lectotype.

This common species is superficially similar to P. plicatum with regards to the number of dactylar tubercles and general carapace shape, but differs strikingly in the form of the G1. In P. ungulatum , the G1 is proportionately shorter, with the pectinated distal part straight, not recurved, and the tip truncate ( Fig. 10 A– D). The G 1 in P. plicatum is more slender than in P. ungulatum , the pectinated distal part curves outwards (hook-shaped) and the tip is rounded ( Fig. 4 A–D).

Although both P. plicatum and P. ungulatum have about the same number of dactylar granules, the form of these granules differ, being distinctly lower and less pronounced in P. ungulatum than in P. plicatum . As discussed earlier, P. plicatum is also more rugose with regards to the outer surfaces of the chelipeds and legs than P. ungulatum . The beige-coloured granules adjacent to the two oblique pectinated ridges on the male manus are also distinctively absent in P. ungulatum .

Geographical distribution. China, Hong Kong, Thailand, Malaysia, Singapore and Indonesia.

Figures

FIGURE 4. Parasesarma plicatum (Latreille, 1803). Male (( 18.5 x 14.4 mm) (ZRC 2001.0850), India, A – D, right G 1; E, abdomen. Scales = 1 mm.

FIGURE 8. Parasesarma ungulatum (H. Milne Edwards, 1853). Colour in life, male (17.3 x 13.8 mm) (ZRC 2008.0815), Papua. A, overall dorsal view; B, frontal view of carapace.

FIGURE 9. Parasesarma ungulatum (H. Milne Edwards, 1853). A – C, lectotype, male (12.1 x 8.4 mm) (MNHN BP 3692), Sulawesi; D, E, male (17.3 x 13.8 mm) (ZRC 2008.0815), Papua; D, dorsal surface of dactylus of left cheliped showing dactylar tubercles; E, left cheliped.

FIGURE 10. Parasesarma ungulatum (H. Milne Edwards, 1853). Male (17.3 x 13.8 mm) (ZRC 2008.0815), Papua. A – D, right G 1; E, abdomen. Scales = 1 mm