Geothelphusa marginata, Naruse & Shokita, 2004

Naruse, Tohru & Shokita, Shigemitsu, 2004, A New Species Of The Freshwater Crab, Previously Assigned To Geothelphusa Miyazakii (Miyake & Chiu, 1965) (Crustacea: Decapoda: Potamidae), From Yaeyama Group, Southern Ryukyus, Japan, Raffles Bulletin of Zoology 52 (2), pp. 555-562 : 557-558

Geothelphusa marginata , new species

Geothelphusa miyazakii - Minei, 1973: 214, Fig. 8, 9G, H; 1981: 80, Pl. 2 (lower); Sakai, 1976: 562 (English text), 347 (Japanese text); Hirata et al., 1988: 25; Environment Agency, 1991: 228; Shy et al., 1994: 807; Okinawa Prefecture, 1996: 382; Shokita, 1996: 348; Segawa, 2000: 243; Kasai & Naruse, 2003: 283.

Geothelphusa sp. 2 - Yoshigou, 1999: 22, Pl. IIL.

Geothelphusa sp. 3 - Yoshigou, 1999: 22, Pl. 2N.

Material examined. – Refer to subspecies accounts (see later).

Comparative material. Geothelphusa miyazakii (Miyake & Minei) (all specimens collected in Taiwan): 1 male (holotype), CL 24.6 mm, ZLKU 10983 , Alilao Village, Shi-Men district , Taipei County, coll. Jui-Kuang Chiu, 28 Jan.1964; 1 female (paratype), CL 26.4 mm, ZLKU 10984 , data same as holotype ; 3 males CLs 20.0– 23.2 mm, 3 females, CLs 20.8–28.3 mm, ZLKU 10137 , Shenkeng, Taipei County , coll. Jui-Kuang Chiu, 3 Oct.1963; 1 male, CL 21.3 mm, 1 female, CL 26.7 mm , ZLKU 10985 , Shenkeng, Taipei County , coll. Jui-Kuang Chiu, 3 Oct.1963; 2 males, CLs 22.1, 23.3 mm, 1 female, CL 16.2 mm , ZLKU 13752 , Patoutzu, Keelung City, coll. Hsiang-Ping Yu, 22 Jun.1972; 2 males, CLs 15.6, 18.8 mm, 1 female, CL 27.0 mm, RUMF-ZC-76, Tinmu, Taipei City , coll. Jhy-Yun Shy, 2 Sep.2001; 1 male, CL 23.6 mm, 1 female, CL 22.3 mm, RUMF- ZC-77, Tinmu , Taipei City , coll. Jhy-Yun Shy, Kari Lee & Tohru Naruse, 18 Feb.2002; 1 male, CL 23.0 mm , NTOU F10094 , National Taiwan Ocean University , Keelung City, coll. Ping-Ho Ho, 1 Jul.1986; 1 male, CL 23.5 mm, 1 female, CL 22.5 mm , NTOU F10095 , Shuangshi, Shihfan, Shangsi , Taipei City, 1 Jun.1982; 1 female, CL 26.3 mm , NTOU F10096 , Wanli / Kingshan, Chishiangshan , Taipei City , 17 Jun.1984; 1 male, CL 11.9 mm, 1 female, CL 22.4 mm , NTOU F10116 , National Taiwan Ocean University , Keelung City, coll. Dar-Yi Wang, 1 Jan.1989; 1 male, CL 21.4 mm , NTOU F10091 , Rayping, Taipei County , coll. Jhy-Yun Shy, 8 May.1993; 3 males, CLs 12.8–19.4 mm 1 female, CL 20.9 mm , NTOU F10317 , Tinmu, Taipei City , coll. Jhy-Yun Shy, 4 Sep.2001; 2 males, CLs 14.3, 18.5 mm , NMNS 3999-001 , Luchiaokeng, Yanmingshan, Taipei City , coll. Yu-Hsi Wang, 25 Jul.1997; 3 males, CLs 10.3–26.6 mm, 2 females, CLs 13.0, 15.1 mm , NMNS 3999-002 , Luchiaokeng, Yanmingshan, Taipei City , coll. L.-S. Chen, 9 Jun.1997; 1 male, CL 10.5 mm , TMCD 2225 , Alilan stream, Taipei County , coll. Tsun-Hsien Wu, Dec.1986; 1 female, CL 20.0 mm , TMCD 2041 , Pingteng Li, Yangmingshan, Taipei City , coll. Chiu-Chu Lu, 20 Jul.1983; 1 male, CL 14.9 mm , TMCD 2043 , Nankung, Taipei City , coll. Yuang Wei, 5 Aug.1984; 1 male, CL 24.8 mm, 1 femlae, CL 21.9 mm , ZRC 1995.606 , Yangmingshan, Taipei City , coll. C.-J. Leu, 26 Jul.1983; 1 male, CL 25.3 mm, 1 female, CL 21.7 mm , ZRC 1998.213 , Keelung City, 1 Jul.1986. Geothelphusa nanshi Shy, Ng & Yu : male (holotype), CL 18.4 mm , NTOU F10198 , Nanshi, Tainan, Taiwan, coll. Jhy-Yun Shy & W. L. Tsay, 7 Aug.1992. Geothelphusa shokitai Shy & Ng : male (holotype), CL 20.5 mm, NSMT-Cr 15176, Uotsuri Island, Senkaku Group , coll. Masatsugu Yokota, 28 May.1991; 1 female (paratype), CL 29.7 mm, NSMT-Cr 15177, data same as holotype .

Diagnosis. – Carapace slightly convex longitudinally and transversely; anterolateral margin cristated, convex, faintly granulated, external orbital angle blunt, epibranchial tooth represented only by small granules. Eyes with relatively small cornea, subdistal part shorter to almost same height with base of peduncle in frontal view. Ambulatory legs relatively long, total length of second ambulatory legs more than two times as long as CL. Male telson bell-shaped, tip of telson reaching imaginary line joining posterior 2/3 of the coxae of chelipeds. G1 sinuous to straight, proximal half of subterminal segment and terminal segment directing inward, and distal half of subterminal segment directing outward; G1 slender, subterminal segment with a knob on proximal outer margin, with rounded lobe on proximal inner margin; synovial membrane variable in shape, distal margin forked, inner margin just swollen laterally or hooked proximally.

Description. – Carapace slightly convex longitudinally and transversely; orbital and frontal margins cristated, infraorbital margin faintly granulated, frontal margin slightly concave medially, anterolateral margin cristated, convex, faintly granulated, present on anterior 2/5 of carapace, external orbital angle blunt, epibranchial tooth represented only by small granules; postorbital and postfrontal cristae low, gradually raised backward, anterolateral region of carapace with several oblique ridges and small pits, posterolateral region with short carinae; H-shaped gastric groove distinct, two large pits on anterior outer part of H-shaped gastric groove, on either side of cervical groove, one large pit located halfway between Hshaped gastric groove and epibranchial tooth, inside of cervical groove, branchial groove represented by wide and shallow transverse hollow.

Eyes with relatively small cornea, subdistal part shorter to almost same height with base of peduncle in frontal view.

Mouth parts similar to those of Geothelphusa miyakoensis Shokita, Naruse & Fujii, 2002 , except for longer distal segment of mandibular palp and longer coxa of maxilla.

Male chelae asymmetric in size and shape, outer surface of manus of major chela smooth, lower margin rough.

Ambulatory legs relatively long, total length of second ambulatory legs more than two times as long as CL; propodus with elliptic cross-section and four longitudinal margins, only anterior dorsal margin lacking row of spines; propodus of first and second ambulatory legs lined by long setae along outer, inner margins, and along midline of ventral surface; dactylus with rectangular cross-section and four longitudinal margins, distal spine of outer dorsal margin of fourth ambulatory leg thin, sharp, locating about middle of dorsal surface.

Male telson bell-shaped, tip of telson reaching imaginary line joining posterior 2/3 of the coxae of chelipeds.

G1 sinuous to straight, proximal half of subterminal segment and terminal segment directing inward, and distal half of subterminal segment directing outward; G1 slender, subterminal segment with a knob on proximal outer margin, with rounded lobe on proximal inner margin; synovial membrane variable in shape, distal margin forked, inner margin just swollen laterally or hooked proximally.

Habitat. – Geothelphusa marginata is formed in shallow, narrow, slow-flowing streams and in small muddy swamps in forests. Crabs were collected under large stones and from burrows.

Distribution. – Ishigaki and Iriomote Islands, Yaeyama Group, Southern Ryukyus, Japan.

Etymology. – Geothelphusa marginata is named for the Latin “marginatum”, meaning “margined”, because of the distinctly convex anterolateral margins of carapace.

Remarks. – Miyake & Chiu (1965) originally described Geothelphusa miyazakii on the basis of specimens obtained from Alilao Village, Shimen District, Taipei County, Taiwan. Minei (1973) was the first to report on specimens from Ishigaki and Iriomote Islands, Southern Ryukyus, which he identified as G. miyazakii . Later, Shy et al. (1994) doubted whether the specimens from Taiwan and Southern Ryukyuan were conspecific. The present study has idetified a number of differences between G. marginata and G. miyazakii sensu stricto, viz., the proximal inner margin of the subterminal segment of G1 (roundly swollen in G. marginata vs. straight in G. miyazakii sensu stricto), the size of the knob on the proximal outer margin of G1 (small vs. large), and the size of the epibranchial tooth (rudiment vs. absent). In addition, there are significant differences between G. marginata and G. miyazaki i in the ratio of the total length of the second ambulatory leg to CL, and in the ratio of the length to width of the propodus of the second ambulatory legs (Tables 1, 2).

Shy et al. (1994) remarked that the terminal segment of the G1 of G. marginata is slender and more elongated than G. miyazakii sensu stricto. However, the ratio of the total length to width of G1 of G. miyazakii sensu stricto is in almost the same range as G. marginata , and the length to the width ratio of the terminal segment of G1 is wider than in G. marginata (Table 1).

The respective populations of G. marginata occurring on Ishigaki and Iriomote Islands differ slightly from one another in morphology and live colouration. We regard these differences as infraspecific in nature because each population does not show any differences in the shape of G1, which is reproductively and taxonomically most important character. As such, we regard two subspecies for the two islands. The subspecific accounts follow (see later).

Geothelphusa marginata also resembles G. nanshi Shy, Ng & Yu, 1994 . However, G. marginata can be distinguished from G. nanshi by the shape of G1 (sinuous in G. marginata vs. gently curved outward in G. nanshi ), the shape of the proximal inner margin of the subterminal segment of G1 (roundly swollen vs. straight), the shape of the external orbital angle (blunt vs. sharp), the form of the anterolateral margin (barely granulated vs. certainly granulated), the condition of the cervical groove (distinct vs. invisible), and the accessory of the propodus of the second ambulatory leg (three rows of spines vs. only two rows of spines on the inner margins).

Geothelphusa marginata is also close to G. shokitai Shy & Ng. However , G marginata is easily differentiated from G. shokitai by the shape of G1 (sinuous in G. marginata vs. almost straight in G. shokitai ), the shape of the dorsal surface of the carapace (convex vs. almost flat), the form of the anterolateral margin (very low granules vs. distinct granules), the shape of the external orbital angle (blunt vs. acute), and the shape and the relative position of the male telson (tip narrow, reaching imaginary line joining proximal 2/3 of the coxae of the chelipeds vs. tip obtuse, reaching imaginary line joining proximal 1/2 of the coxae of the chelipeds).