Parasesarma affine (De Haan, 1837)

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 : 8-11

Parasesarma affine (De Haan, 1837)

( Figs. 5–7 )

Grapsus (Pachysoma) affinis De Haan, 1837: 66 , pl. 18, fig. 5.

Sesarma affinis — H. Milne Edwards 1853: 183. – Heller 1862: 68.

Sesarma quadrata var. affinis — Ortmann 1894: 724.

Sesarma (Parasesarma) plicatum — Sakai 1976: 656, pl. 226, fig. 1.

Parasesarma plicatum — Miyake 1983: 239.

Sesarma (Pachysoma) plicatum — Yamaguchi & Baba 1993: 481 (lectotype designated).

Sesarma (Parasesarma) plicata — Crosnier 1965: 65, figs. 83, 88, 93, 105. – Dai et al. 1986: 490, pl. 69 (2), fig. 275 (2). – Dai & Yang 1991: 537, pl. 69 (2), fig. 275 (2). – Shen 1932: 191, text fig. 119 –120, pl. 7, fig. 8. – Shen & Dai 1964: 135. – Sakai 1939: 683, pl. 110, fig. 2.

Parasesarma plicatum — Wang & Liu 1996: 117, figs. 150, 151. – Ng et al. 2001: 43.

Parasesarma affine — Ng et al. 2008: 222.

Types. Grapsus (Pachysoma) affinis De Haan, 1837 . Lectotype, male (19.4 x 14.9 mm) (RMNH 129a). Paralectotype (dry) 1 male (carapace width 24.5mm), 1 female (carapace width 24.0 mm) (RMNH 129b).

Material examined. 1 male (18.6 x 14.4 mm) ( ZRC 1967.11.9.1), 1 female (23.4 x 17.8 mm) ( ZRC 1967.11.9.2), Misaki, Sagami Bay, Japan, coll. T. Sakai, 1966. – 2 males (29.1 x 23.5 mm, 30.0 x 23.7 mm) ( ZRC 1995.417), Kandellia zone, on creek banks and base of tree trunks, Mai Po Marshes, New Territories, Hong Kong, China, coll. W. P. W. Kwok, 1993. – 1 male (28.2 x 22.4 mm) ( ZRC 1975.6.30.5), Shum Chun River, Mai Po Marshes, New Territories, Hong Kong, China, coll. C. L. Soh, 15 June 1975. – 4 males (25.1 x 19.9 mm, 26.5 x 21.4 mm, 26.1 x 20.4 mm, 25.5 x 20 mm) ( ZRC 1975.6.30.6-9), Shum Chun River, Mai Po Marshes, New Territories, Hong Kong, China, coll. C. L. Soh, 15 June 1975. – 3 males (11.9 x 8.1 mm, 16.8 x 12.7 mm, 13.1 x 10.0 mm) ( ZRC 1998.339), 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 (27.7 x 22.0 mm) ( ZRC 1998.1180), Qidong, Jiangsu Province, China, coll. N. K. Ng, 2 May 1996. – 2 males (24.6 x 19.0 mm, 26.4 x 21.6 mm), 1 female (15.6 x 12.6 mm), Miaoli, Chunan mangrove, Taiwan, coll. H.-C. Liu & C. D. Schubart, 17 September 1999.

Diagnosis. Carapace 1.35 times broader than long ( Figs. 5 A, 6A); mesogastric, cardiac regions well defined; lateral carapace surface lined with strong oblique striae; carapace surface with scattered tufts of setae, lateral margins with short setae. Postfrontal margin with 4 distinct lobes, separated by narrow grooves. External orbital tooth triangular, directed upward, fused with entire lateral carapace margin; greatest width of carapace at external orbital tooth.

Chelipeds subequal ( Figs. 5 B, 6C), large, robust. Merus with outer margin tuberculate, with subdistal spine; inner margin tuberculate ending in large subdistal spine; outer surface striated, inner surface with longitudinal row of setae, scatterd setae near upper margin. Carpus with inner angle not produced, outer margin, across dorsal surface striated. Upper surface of palm with 2 transverse pectinated crests ( Fig. 6 D). Primary crest with 17–23 teeth. Secondary crest well developed, shorter than primary, with 9–13 teeth. Outer surface of palm naked, striated proximally, granular distally, near upper margin of palm; inner surface of palm with several tubercles. Fixed finger rounded, granular on outer surface. Dorsal surface of dactylus with 8 or 9 tubercles ( Fig. 6 E), small proximally, progressively larger distally; all tubercles distinct, rounded, each tubercle with fine longitudinal lines, prominent transverse ridge on tip. Several low tubercles on proximal third of upper surface, proximal half of inner edge of dorsal surface with row of large tubercles. Cutting edges with large teeth.

Walking legs robust, flattened, broad ( Fig. 6 A); second, third pairs sub-equal, longer than others, about 1.5 times carapace width. Merus of third leg approximately twice as long as wide; upper margin of merus with acute subdistal spine. Carpus with 2 accessory carinae on outer surface. Propodi of legs 2–5 3 times as long as wide, short stiff brush-like setae along dorsal margin, ventral margins with few long, stiff setae. Dactylus almost same length as propodus, slightly recurved, terminating in acute corneous tip, dorsal margin with short, stiff setae.

Male abdomen relatively broad ( Figs. 6 B, 7E). Telson semicircular, evenly rounded, as long as somite 6; somite 6 more than twice 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 slender ( Fig. 7 A–D), apical process long, bent to form a 45º angle, produced, corneous part long, straight. Setae long, simple, originating at base of apical process. G2 very short.

Female chelipeds smaller than in male, second pectinated crests on palm replaced by transverse row of tubercles, dactylar tubercles indistinct.

Colour. The species has been well illustrated in various Japanese and Taiwanese colour publications (see Miyake 1983; Sakai 1976; Wang & Liu 1996). The chela is bright orange in adult specimens, with the fingers deep-red ( Fig. 5 ). The colours of the carapace and chelae are similar to those of P. plicatum , although the red on the fingers appear to be somewhat darker in the latter species ( Fig. 2 ).

Remarks. Parasesarma affinis is superficially very similar to P. plicatum externally, but they differ markedly in the number of dactylar tubercles and in the G1 structure (see Discussion for P. plicatum ) and it is rather surprising that their separate identities have been confused for so long.

The description and figures of P. plicatum provided by Crosnier (1965) are of Japanese material and agree very well with our material and the types, and we are confident they are conspecific.

The ecology of this species has been studied by Kwok & Lee (1995), who discussed the herbivorous behaviour of P. affine (as P. p l i c a t a).

Geographical distribution. Japan, Hong Kong, China, Taiwan.

Figures

FIGURE 2. Parasesarma plicatum (Latreille, 1803). Colour in life. A, male (19.0 x 15.2 mm) (ZRC 2000.1913), Phuket, Thailand; B, C, male (21.3 x 18.11 mm) (ZRC 2008.0816), Lombok Island, Indonesia. A, B, overall dorsal views; C, frontal view showing chelipeds.

FIGURE 5. Parasesarma affine (De Haan, 1837). Colour in life. A, carapace; B, frontal view (Specimen from Taiwan, not preserved; photographs by H. - T. Shih).

FIGURE 6. Parasesarma affine (De Haan, 1837). Lectotype male (19.4 x 14.9 mm) (RMNH 129), Japan. A, overall dorsal view; B, frontal view of carapace; C, ventral view showing anterior part of thoracic sternum, abdomen; D. left cheliped; E, dorsal surface of dactylus of left cheliped showing dactylar tubercles.

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.