Paracleistostoma meilanense, Liu, Han Lun & Huang, Jian Rong, 2016

Liu, Han Lun & Huang, Jian Rong, 2016, A new species of Paracleistostoma De Man, 1895 (Crustacea: Decapoda: Brachyura: Camptandriidae) from Haikou, Hainan Province, China, Zootaxa 4121 (3), pp. 346-350 : 346-349

Paracleistostoma meilanense , n. sp.

Material examined. Holotype: male (7.00 × 5.01 mm) ( SYSU), Haikou, Hainan, China, coll. H. L. Liu, July 2015. Paratype: male (6.82 × 4.98 mm) ( SYSU), same data as holotype.

Comparative material. Paracleistostoma depressum de Man, 1895: 1 male (8.20 × 5.96 mm) ( SYSU), Haikou, Hainan, China, coll. H. L. Liu, July 2015; Paracleistostoma tomentosa Yang & Sun, 1993: 1 male (8.68 × 6.63mm) ( SYSU), Haikou, Hainan, China, coll. H. L. Liu, July 2015.

Diagnosis. Carapace transversely hexagonal; mesobranchial, metabranchial regions covered with sparse pubescence ( Fig. 1 A). Front convex in median section, divided in 2 parts ( Fig. 1 A). Outer orbital angle triangular, protruding forward ( Fig. 1 A). Third maxilliped broad, completely covering buccal field ( Fig. 1 B). Ischium rectangular, length sub equal to breadth ( Fig. 1 C). Merus about 1.3 times as long as broad, with rounded, convex edges ( Fig. 1 C). Chelipeds slender, carpus longer than wide, inner margin of movable finger unarmed ( Figs.1 B, 3A). First male pleopod smooth without pubescence, distal portion recurved ( Fig. 2 A), inner margin convex, ovate. Tip of distal portion long, flexed as obtuse angle ( Fig. 2 A). Male pleon with somites 2–5 fused; sixth somite greater in breadth than length; terminal somite (telson) rounded quadrangle, longer than sixth ( Fig. 1 B).

Description. Carapace transversely hexagonal, surface slightly convex, mesobranchial, metabranchial regions covered with sparse pubescence. Regions demarcated. Gastrocardiac region with H-like groove. Front, as long as one fourth of greatest breadth of carapace, medially convex, divided into 2 parts. Dorsal obital margin ridged in median region, concave on both sides; outer orbital angle triangular, protruding forward. Anterolateral margin of carapace straight. Granular ridge extending obliquely downward, backward from median to posterior margin. Third maxilliped broad, completely covering buccal field. Ischium rectangular, with length sub equal to breadth, more than 2 times longer than merus measured along inner edge, covered with short dense setae from outer distal angle to inner proximal angle, inner margin. Merus about 1.3 times as long as broad, with rounded, convex edges. Exopod narrow with well-developed flagellum.

Chelipeds slender. Merus trigonal, with scattered long pubescence on dorsal margin, inner-ventral margin. Carpus longer than wide, inner surface with scattered pubescence near dorsal margin. Propodus smooth, longer than wide, inner margin of movable finger smooth with no tooth, immovable finger with sparse short pubescence in distal part of inner margin. Fingers narrow in basal portion, broadened in distal portion, gap present when closed. Ambulatory legs stout, especially third pair. First ambulatory legs smooth, second, third, fourth ambulatory legs covered with dense pubescence, covered with mud except dactylus. First male pleopod smooth without pubescence, distal portion recurved, slim; inner margin convex, ovate, outer margin slightly protuberant. Tip of distal portion long, flexed in an obtuse angle. Somites 2–5 of the male pleon fused; sixth somite wider than long; terminal somite as rounded quadrangle, longer than sixth.

Etymology. Paracleistostoma meilanense is named after the type locality, Meilan district, in Haikou city, Hainan Province, China.

Colour. Carapace dark green, pleon and ambulatory legs light yellow. ( Fig. 1 A)

Ecology. The new species inhabits mud burrows in the upper intertidal zone along with P. depressum and P. tomentosa . The depth of the burrows is no more than 20 cm. The crabs are active when tide falls and they often change their burrows. Brooding females have been observed in July.

Character P. meilanense n. sp. P. depressum P. tomentosa

Cheliped Slender ( Fig. 1 B, 3A) Stout ( Fig. 3 C) Slender ( Fig. 3 B) Remarks. P. meilanense n. sp. is very similar to P. depressum and P. tomentosa in general morphology, and as with most Paracleistostoma species, there are almost no differences in the carapace and ambulatory legs among the three species. The new species can nevertheless be distinguished from P. depressum and P. tomentosa by the shape of its cheliped and first male pleopod. The chelipeds of P. meilanense n. sp. are slender with no tooth on the movable finger, whereas that of P. depressum are stout with a blunt, stout tooth on the movable finger. The cheliped carpus of P. meilanense n. sp. is longer than wide, whereas that of P. depressum is a rhomboic with length sub equal to width. The sixth somite of the male pleon of the new species is shorter than the terminal somite, whereas it is opposite in P. depressum . In the new species somites 2–5 of the male pleon are fused; in P. depressum , only the somites 3–5 are fused. First male pleopod of P. meilanense n. sp. and P. depressum is superficially similar, but their tip is slightly different. The first male pleopod of P. meilanense n. sp. has a long tip flexed as an obtuse angle while P. depressum has flatter and smoother tip. Moreover, the first male pleopod of P. meilanense n. sp. is more convex than that of P. depressum on the ovate region of inner margin. Although P. meilanense n. sp. and P. tomentosa are similar in almost every aspect, their first male pleopod are different. The distal portion of the first male pleopod of P. meilanense n. sp. is slightly convex on the inner margin, whereas that of P. tomentosa is globular, or “beansprout” shape. This difference shows that P. meilanense n. sp. and P. tomentosa belong to two species.

Figures

FIGURE 1. Paracleistostoma meilanense n. sp. A, dorsal view of male holotype (7.00 × 5.01 mm) (SYSU). B, ventral view of male holotype (7.00 × 5.01 mm) (SYSU) showing anterior thoracic sternum, chelipeds, and pleon. C, left third maxilliped of male paratype (6.82 × 4.98 mm) (SYSU).

FIGURE 2. Left first male pleopods of three species of Paracleistostoma (ventral views). A, Paracleistostoma meilanense n. sp., male paratype (6.82 × 4.98 mm) (SYSU). B, Paracleistostoma depressum de Man, 1895, male (8.20 × 5.96 mm) (SYSU). C, Paracleistostoma tomentosa Yang & Sun, 1993, male (8.68 × 6.63 mm) (SYSU).

FIGURE 3. Chelipeds of three species of Paracleistostoma. A, Paracleistostoma meilanense n. sp. male holotype (7.00 × 5.01 mm) (SYSU). B, Paracleistostoma depressum de Man, 1895, male (8.20 × 5.96 mm) (SYSU). C, Paracleistostoma tomentosa Yang & Sun, 1993, male (8.33 × 6.64 mm) (SYSU).