Minutomon shanweiense, Huang, Chao, Mao, Si Ying & Huang, Jian Rong, 2014

Huang, Chao, Mao, Si Ying & Huang, Jian Rong, 2014, Two new potamid crabs, Yuexipotamon arcophallus new genus, new species and Minutomon shanweiense new genus, new species, (Crustacea: Decapoda: Brachyura: Potamidae) from southern China, Zootaxa 3764 (4), pp. 455-466 : 461-465

Minutomon shanweiense , new species

Material examined. Holotype: male (13.4 × 10.8 mm) ( SYSU 001126), Shanwei, Guangdong, China, coll. J. W. Luo, March 2013. Paratypes: 1 female (allotype) (16.9 × 13.1 mm) ( SYSU 001127), Shanwei, Guangdong, China, shallow creek, under rock, coll. C. Huang, April 2013; 2 males (13.3 × 10.4 mm, 13.1 × 10.4 mm) ( SYSU 001128– 001129), same data as allotype, 2 males (10.0 × 8.1 mm, 10.3 × 8.3 mm) ( SYSU 001130–001131), 1 female (11.9 × 9.7 mm) ( SYSU 001132) Shanwei, Guangdong, China, coll. J. W. Luo, March 2013, 2 males (13.6 × 10.7 mm, 9.6 × 7.9 mm) ( ZRC 2013. 1806), same data as allotype, 2 females (14.3 × 11.3 mm, 14.4 × 11.5 mm) ( ZRC 2013. 1806), same data as allotype.

Diagnosis. As for genus.

Description. Carapace subquadrate; dorsal surface slightly convex transversely, longitudinally; surface with weak rugae on anterolateral regions ( Fig. 7 A). Front slightly deflexed, almost straight on dorsal view ( Fig. 7 A). Epigastric cristae low, separated by a narrow gap ( Fig. 7 A, C). Postorbital cristae blunt, not obvious, laterally expanded to join epigastric cristae and anterolateral margins ( Fig. 7 A, C). Branchial regions generally flat ( Fig. 7 A). Cervical groove shallow, inconspicuous ( Fig. 7 A). Mesogastric region generally flat ( Fig. 7 A). External orbital tooth bluntly triangular with convex margins; separated from anterolateral margin by a gap ( Fig. 7 A, C). Epibranchial tooth prominent, granular ( Fig. 7 A, C). Anterolateral margin cristate, lined with approximately 17 granules; terminal part bent inwards ( Fig. 7 A). Posterolateral margin slightly rugose, covered with short setae ( Fig. 7 A). Supraorbital and infraorbital margins cristate; lined with numerous inconspicuous granules ( Fig. 7 C). Suborbital, sub-hepatic and upper parts of pterygostomial region pitted ( Fig. 7 C). Third maxilliped with merus about 1.1 times as broad as long, ischium about 1.5 times as long as broad ( Fig. 7 C, 8D). Merus subquadrate, pitted; ischium slender, trapezoidal, with distinct median sulcus; exopod reaching to proximal third of merus, with long flagellum reaching almost entire width of merus; upper-inner margin of ischium auriculiform ( Fig. 7 C, 8D). Posterior margin of epistome broad, median triangular lobe large, bluntly triangular, lateral margins straight ( Fig. 7 C).

Chelipeds slightly unequal, surface pitted ( Fig. 7 A). Merus cross-section trigonal; margins crenulated ( Fig. 7 C). Carpus with blunt spine at inner-distal angle, spinule at base ( Fig. 7 A). Palm of larger chela about 1.3 times as long as high. Movable finger equal to fixed finger. Inner margin of fingers with rounded, blunt teeth; with small gap when closed.

Ambulatory legs slender with dense long setae on dactylus, propodus, carpus, comparatively sparse setae on merus ( Fig. 7 A). Last leg with propodus about 2 times as long as board, approximately same length as dactylus ( Fig. 7 A).

Thoracic sternum pitted ( Fig. 7 B). Sternites 1, 2 completely fused to form triangular structure; sternites 3, 4 fused with incomplete median suture ( Fig. 7 B, 9C). Anterior thoracic sternites relatively wide ( Fig. 7 B). Male sterno-abdominal cavity reaching to imaginary line joining median part of coxae of cheliped; median longitudinal groove between sternites 7, 8 deep ( Fig. 7 B).

Male abdomen triangular, somite 6 about 2.4 times as broad as long; lateral lines almost straight; telson about 1.4 times as broad as long, with straight to slightly convex lateral margins ( Fig. 7 B).

G1 slender, straight, knife-shaped, inner margin slightly concave, tip of terminal segment reaches well beyond suture between sternites 5, 6 in situ; terminal segment slightly rugose with folds present at the tip; inner distal angle very blunt, sloping downwards; outer distal angle large, bluntly triangular; subterminal segment about 2.1 times as long as terminal segment ( Fig. 7 D, 8B, C, 9A, B). G2 with subdistal segment about 2.1 times as long as distal segment ( Fig. 8 A).

Variation. The tip of the terminal segment of the G 1 may vary in sharpness and shape.

Etymology. The name is derived from the type locality, Shanwei City, Guangdong Province, China.

Colour. Generally dark brown to yellowish brown. ( Fig. 6 )

Ecology. Minutomon shanweiense , new genus, new species, can be found residing under rocks in fast flowing mountain streams. Collection can be difficult as this species is small and cryptic and hardly ever leaves the protection of the large rocks under which they hide, even at night. The river system has a number of benthic fishes like Rhinogobius zhoui Li & Zhong, 2009 , and R. duospilus Herre, 1935 (Gobiidae) that can easily prey on juveniles and small individuals of the crab. Minutomon shanweiense , new species, is sympatric with an unidentified species of Nanhaipotamon .

Figures

FIGURE 6. Minutomon shanweiense, new genus, new species, colours in life, male holotype (13.4 × 10.8 mm) (SYSU 001126).

FIGURE 7. Minutomon shanweiense, new genus, new species, male holotype (13.4 × 10.8 mm) (SYSU 001126). A, dorsal overall view; B, ventral view showing anterior thoracic sternum and abdomen; C, frontal view of carapace; D, ventral view showing sterno-abdominal cavity with right G 1 in situ (left G 1 removed).

FIGURE 8. Minutomon shanweiense, new genus, new species, male holotype (13.4 × 10.8 mm) (SYSU 001126). A, left G 2; B, left G 1 (ventral view); C, G 1 terminal segment (ventral view); D, left third maxilliped. (white bar = 1.0 mm)