Chiromantes magnus, Komai, Tomoyuki & Ng, Peter K. L., 2013

Komai, Tomoyuki & Ng, Peter K. L., 2013, A new species of sesarmid crab of the genus Chiromantes (Crustacea: Decapoda: Brachyura) from the Ogasawara Islands, Japan, Zootaxa 3681 (5), pp. 539-551 : 539-549

Chiromantes magnus n. sp.

( Figs. 1A , 2– 5 )

Sesarma dehaani .— Stimpson 1858: 106 (part); 1907: 134 (part).— Parisi 1918: 111 (part).— Asakura et al. 1993: 10. Holometopus dehaani .— Takeda & Miyake 1976: 113 (list).

Chiromantes dehaani .— Marumura & Kosaka 2003: 66 (part).— Takeda & Ueshima 2006: 93 (part).— Komatsu 2011: 277 (list).

Material examined. Holotype: male (47.2 × 52.2 mm), CBM-ZC 11452, Renju Valley, Chichi-jima I., Ogasawara Is., 23 September 2008, coll. H. Tachikawa.

Paratypes: 1 male (37.9 × 41.8 mm), CBM-ZC 11453, Kominato, Chichi-jima I., 10 December 2005, coll. T. Komai; 1 male (25.5 × 28.2 mm), CBM-ZC 11454, Kopepe Beach, Chichi-jima I., 11 December 2005, coll. T. Komai; 1 male (40.8 × 45.2 mm), RUMF-ZC 2160, same locality, 22 June 2010, coll. Y. Fujita; 1 ovigerous female (40.2 × 43.5 mm), RUMF-ZC 2362, same data; 1 male (44.0 × 49.8 mm), RUMF-ZC 2360, same locality, 27 June 2010, coll. Y. Fujita; 4 males (smallest 15.8 × 18.2 mm, largest 26.1 × 28.5 mm), 1 female (25.2 × 27.9 mm), CBM- ZC 11455, Chichi-jima I., August 2008, coll. K. Iwasaki and family; 1 male (44.4 × 50.1 mm), CBM-ZC 11456, 1 male (45.6 × 50.6 mm), ZRC 2013.0173, same data as holotype; 1 male (45.5 × 50.3 mm), CBM-ZC 11457, Okumura River, river mouth, 28 September 2008, coll. H. Tachikawa; 1 female, CBM-ZC 11600, Kiyose, Chichijima I., 14 July 2009, coll. T. Komai; 1 male (25.3 × 28.3 mm), RUMF-ZC 2361; same locality, 25 June 2010, coll. Y. Fujita.

Comparative material. Chiromantes dehaani . Lectotype, male (35.7 × 39.5 mm), RMNH. CRUST.D.157, Japan, 1823–1829, coll. von Siebold. Non-types: JAPAN – 1 male (35.0 × 38.5 mm), CBM-ZC 165, Obitsu River estuary, Kisarazu, Chiba Prefecture, July 1990, coll. T. Furota; 1 male (28.3 × 31.0 mm), CBM-ZC 169, Hanami River, Chiba, Chiba Prefecture, 5 October 1990, coll. Nakano; 1 male (25.4 × 28.3 mm), CBM-ZC 11406, Yahata Channel, Ichihara, Chiba Prefecture, 30 August 2012, coll. J. Takayama; 6 males (22.0 × 23.9 mm to 37.7 × 42.0 mm), 3 females (22.0 × 23.9 mm to 26.9 × 29.5 mm), CBM-ZC 11458, Kaneda, Kisarazu, May 2009, coll. T. Komai; 1 male (24.5 × 27.3 mm), ZRC 1968.4.22.12, 1968, coll. T. Sakai; 1 female (21.5 × 24.3 mm), ZRC 1970.8.27.1, Kamakura, Kanagawa Prefecture, Sagami Bay, 1968, coll. T. Sakai; 2 males (20.2 × 22.0 mm, 21.1 × 23.5 mm), CBM-ZC 7576, Tatara River, Fukuoka, Fukuoka Prefecture, March 2003, coll. Y. Matsuzawa; 1 ovigerous female (19.4 × 21.4 mm), ZRC 2002.226, river mouth, Izaku River, Satsuma Peninsula, Kagoshima Prefecture, 30 August 2000, coll. H. Suzuki; 2 males (larger 20.8 × 23.4 mm), 2 females (larger 22.0 × 25.2 mm), ZRC 2012.0057, Koutsuki River, Kagoshima City, 24 October 2011, coll. P. K. L. Ng et al.; 1 male (23.0 × 25.6 mm), 1 ovigerous female (23.9 × 27.4 mm), CBM-ZC 3129, Tomari, Kume I., Ryukyu Is., 12 June 1995, coll. T. Komai; 1 male (36.6 × 38.3 mm), ZRC 2011.1026, Zenda Forest Park, Kume I., Ryukyu Is., 15 November 2009, coll. T. Naruse et al.; 3 males (largest 35.5 × 38.4 mm), 1 female (23.7 × 26.6 mm), ZRC 2011.1027, Zenda Forest Park, Kume I., Ryukyu Is., 17 November 2006, coll. P. K. L. Ng et al.; 1 female (31.7 × 36.2 mm), CBM-ZC 9870, Ohtomi, Iriomote I., Yaeyama Is., 29 April 1998, coll. N. Shikatani; 1 male (32.4 × 35.4 mm), ZRC 2000.2263, Iriomote I., Ryukyu Is., 15 June 2000, coll. Y. Cai & N. K. Ng. TAIWAN – 1 male (25.7 × 28.3 mm), ZRC 2001.25, near Tashi, northern Taiwan, 2000, coll. K.-X. Lee; 1 male (23.9 × 26.2 mm), ZRC 2009.0871, Meilun stream, Hualien, 27 January 2002, coll. H.-C. Liu; 1 male, 1 female, ZRC 2000.1847, Hsinfeng mangroves, Hsinchu, 17 September 1999, coll. H.-C. Liu & C. D. Schubart; 1 male, ZRC 2002.414, Lion Museum, Peikuan, Toucheng town area, 21 June 2002, coll. H.- C. Liu. CHINA. 2 males, ZRC 2010.0326, purchased, aquarium trade, supposedly from Guangzhou, China, 2010, coll. P. K. L. Ng. HONG KONG. 2 males (27.6 × 29.6 mm, 26.8 × 30.0 mm), ZRC 2002.223, July 2000, coll. H. H. Tan; 2 males (21.5 × 24.7 mm, 19.5 × 22.5 mm), 1 female (21.2 × 24.8 mm), ZRC 1975.6.30.12-14, Tai Po, New Territories, 8 June 1975, coll. C. L. Soh.

Chiromantes neglectus : CHINA. 17 males (smallest 20.0 × 22.7 mm, largest 31.8 × 35.6 mm), 6 females (smallest 14.5 × 16.7 mm, largest 23.7 × 27.2 mm), ZRC 1998.310, 1 male (25.5 × 30.2 mm), 1 female (21.5 × 25 mm), CBM-ZC 11459, Qidong, Lusi, Shanghai, coll. Y. Y. Li, 1 May 1996; 1 male (28.0 × 31.7 mm), ZRC 1998.309, Qi Dong, Lusi, Shanghai, coll. Y. Y. Li et al., 1 May 1996; 1 male, ZRC 2010.0420, Chongming, west of Shiqiao River, 31º38.37’N 121º21.496’E, coll. B. Y. Au, 15 July 2010.

Description. Carapace ( Figs. 1A , 2 A) subquadrate, 1.1 times wider than long, maximum width across posterolateral angles; dorsal surface slightly convex longitudinally, nearly flat transversely, regions moderately well defined; anterior part slightly granular, with scattered tufts of short stiff setae (setae sometimes worn away in large specimens); gastric region slightly rugose with microscopic transverse striae; posterior part of branchial region with 6–9 obliquely transverse striae. Front slightly more than 0.5 times fronto-orbital width, deflexed nearly perpendicularly from postfrontal lobes ( Fig. 2 B), anterior margin with broad, shallow median concavity; lateral angles rounded. Postfrontal lobes distinct, divided by relatively broad, deep grooves, median lobes broader than laterals. Lateral margins slightly convergent posteriorly towards posterior carapace margin, gently arcuate in lateral view; external orbital angle acute, directed anteriorly, with 2 low, obtuse anterolateral lobes posterior to it. Supraorbital margin evenly concave; inner surface of orbit with dense stiff setae; infraorbital ridge slightly sinuous, setose, with obtusely triangular inner tooth. Epistome ( Fig. 2 B) trilobate, lined with beaded granules. Interantennular septum about 0.2 times width of front.

Eye ( Fig. 2 A) not extending beyond external orbital tooth; eyestalk slightly constricted at base of cornea. Basal segments of antennular, and antennal peduncles almost in contact, not separated by septum, antennal flagellum entering orbit ( Fig. 2 B).

Third maxilliped with ischium and merus subequal in length. Merus concave on outer surface, with mesial carina bearing dense row of setae extending onto lateral margin of ischium ( Fig. 2 B). Palp (carpus to dactylus) flattened, reaching proximal fifth of merus in situ. Exopod concealed beneath ischium and merus, slender, weakly widened subdistally, slightly reaching beyond midlength of merus, with moderately long flagellum.

Male chelipeds ( Figs. 1A , 4 A, B) subequal, large, robust. Merus trigonal in cross section; dorsal margin with prominent, weakly granular keel; outer surface coarsely granular, outer ventral margin delimited by single or double row of coarse granules; inner surface shallowly concave, upper one-third with covering of short stiff setae, and with prominent longitudinal row of stiff setae along lower one-third, inner ventral margin sinuous, distinctly ridged, with single or double row of spiniform granules or tubercles; ventral surface slightly concave, with subdistal row of granules. Carpus with inner angle not clearly delineated; dorsal surface coarsely granular, with granular submarginal carina emerging into inner marginal carina distally; inner surface convex, with scattered granules medially. Palm ( Fig. 4 B) somewhat compressed, higher than long; dorsal surface with low, coarse granules, without pectinated crest, inner carina prominent, extending onto mesial surface along proximal margin; outer surface covered with low granules of various sizes, granules adjacent to ventral margin proximal to fixed finger larger than others, forming prominent cluster; inner surface with prominent tubercles on upper one-third, remainder with scattered blunt granules; ventral margin rounded. Fingers slightly curved inward, with narrow hiatus when closed. Fixed finger flattened, triangular, basal height about half of height of palm; outer surface almost smooth; cutting edge with row of tiny to small, blunt or subacute teeth. Dactylus exceeding twice length of palm; dorsal surface with numerous minute granules (worn in large specimens), but without row of tubercles; cutting edge with row of tiny to small, blunt or subacute teeth.

Female chelipeds proportionally smaller than in males; palm with outer surface less granular, no crest extending from dorsal to mesial surfaces.

Ambulatory legs ( Fig. 1A ) relatively long, third leg longest, length of merus to propodus 1.4–1.7 times (mean 1.52, SD 0.0655, n = 16) carapace width; distal angle of merus of second ambulatory leg reaching level of external orbital angle when stretched anteriorly. Anterior surfaces of coxae each with mat of setae, those of second and third legs more prominent. Meri with extensor margins slightly convex, sharply carinate, each bearing triangular subterminal tooth; dorsal surfaces with some transverse striae (first to third) or with sparse granules (fourth); flexor surfaces flanked by margins with clusters of short, elongated, stiff setae (first and second legs), sparse row of long stiff setae (third leg) or only few short setae (fourth leg). Carpi with dense mats of short stiff setae, mixed with sparse long setae, on extensor surfaces; dorsal surfaces each with 2 ridges, upper ridge setose, lower ridge almost glabrous. Propodi each with setal mat, consisting of mixture of short and long stiff setae, on extensor and flexor surfaces (density of setae decreasing posteriorly, flexor surface of fourth leg with sparse setae); flexor distal margin of fourth leg with row of corneous spinules. Dactyli subconical, slightly curving, terminating in acute corneous claws, 0.7–0.8 times as long as propodi; extensor and flexor surfaces with mat of setae decreasing in density toward posterior.

Male thoracic sternites 1–3 ( Fig. 3 A, B) short, partially obscured by setae on third maxillipeds; sternites 1/2, 3, and 4 well separated, borders lined with stiff setae; sternite 4 wide, widened anteriorly, sterno-abdominal cavity just short of reaching suture between sternites 3/4. Sternites 5–7 almost glabrous except for a few tufts of very short setae.

Male abdomen ( Fig. 3 A, B) gradually narrowed towards somite 6; somite 3 widest; somite 6 ( Fig. 5A ) subtrapezoidal, about twice wider than long, distolateral margin gently convex. Telson ( Fig. 5A ) subequal in length to somite 6, approximately as long as wide.

Female abdomen with somite 6 about 3.2 times wider than long, distolateral angles reaching level of proximal one-third of telson ( Fig. 5B ). Telson ( Fig. 5B ) subsemicircular, 1.3 times as wide as long.

Vulva with ( Fig. 5 F) terminally subtruncated operculum.

First gonopod ( Fig. 5C ) almost straight in ventral view, faintly curving dorsally, cross section trigonal, ventral surface with distinct longitudinal ridge and with deep groove; terminal process ( Fig. 5 D, E) roundly truncate distally, curved laterally at 65° angle from vertical against shaft; base of terminal process covered with numerous stiff setae. Second gonopod short, without flagellum.

Size. Largest male 47.2 × 52.2 mm; largest female (ovigerous) 40.2 × 43.5 mm.

Color in life. ( Figs. 1A , 3 A). Carapace dorsal surface mottled with black-brown and yellowish-gray or brownish-gray with several pale-gray spots; anterolateral margin with alternating patches of gray and dark brown. Ischium of third maxilliped whitish. Coxa to ischium of chelipeds reddish-brown; merus and carpus grayish-brown or yellowish-gray; chela pale olive or yellowish-gray, darker on dorsal surface. Ambulatory legs usually grayishbrown, striae on meri and ridges on carpi dark brown. Thoracic sternum and abdomen light grayish-brown or light yellowish-gray, anterior thoracic sternites with tinge of reddish-brown.

Distribution and habitat. So far known only from Chichi-jima I., Ogasawara Is., and probably endemic to the area. Individuals occur in estuarine areas to middle parts of rivers or streams where tidal influence is completely absent, sometimes extending to adjacent marsh areas, and sometimes found in burrows under rocks ( Kobayashi & Satake 2009; T. Komai, personal observation). Chiromantes dehaani s. str. is normally found in burrows under rocks, sometimes dozens of metres from the nearest body of water. They can be found next to the seafront along coastal parks as well as along the rocky banks of streams and rivers, sometimes several kilometres from the sea. These streams invariably are connected to the sea and are under tidal influence (Kobayashi 2000; unpublished data). More ecological work will need to be done to see if C. magnus n. sp. actually habitat preferences different from those of C. dehaani s. str. as suggested by Kobayashi & Satake (2009), and/or if the differences are affected by the relatively small size of the Ogasawara Is.

Etymology. From the Latin magnus (“big”) in reference to the large adult size of the new species when compared to the allied C. dehaani .

Remarks. Ng & Liu (1999: 230) first pointed out that Chiromantes Gistel, 1848 , is polyphyletic. Ng et al. (2008) provisionally referred nine species to Chiromantes , but noted that C. dehaani must be transferred to a separate genus, together with C. boulengeri (Calman, 1920) , C. neglectus (De Man, 1887) , Pseudosesarma patshuni (Soh, 1978) , P. crassimanum (De Man, 1887) , P. johorensis (Tweedie, 1940) , P. moeschi (De Man, 1892) , Sesarmops sinense (H. Milne Edwards, 1853) , and Sesarmops intermedium (De Haan, 1835) . A molecular analysis using partial mitochondrial 16S rRNA by Naderloo & Schubart (2009) also supports the polyphyly of Chiromantes , although their molecular tree is not always consistent with the groupings recognized by Ng et al. (2008). The second author and C. Schubart are currently revising Chiromantes and allied genera and as such, the generic assignment of the present new species is provisional pending the results of this study. This revision will also give more detailed diagnoses and redescriptions of C. dehaani and C. neglectus , as well as discuss their taxonomy at length.

The type series of C. dehaani is preserved in RMNH ( Yamaguchi & Baba 1993). Examination of the lectotype ( Fig. 6 ) confirmed that the present comparative specimens from mainland Japan, Ryukyus, China, Hong Kong and Taiwan are identical with the type series. Chiromantes magnus n. sp. can easily be distinguished from C. dehaani by the proportionally longer ambulatory legs (cf. Figs. 1A , B, 6A). The combined length of the merus to propodus of the third ambulatory legs is 1.4–1.7 times (mean 1.52, SD 0.0655, n = 16) the carapace width of C. magnus n. sp. in contrast to 1.2–1.4 times (mean 1.36, SD 0.0712, n = 17) in C. dehaani . Ambulatory leg proportions have been reported to vary in some degree in freshwater sesarmids in Jamaica ( Schubart et al. 2010). However, this has not been documented in marine sesarmids in Asia, and we have not observed any significant variation in leg proportions in the present large series of Chiromantes specimens we have on hand. In C. magnus n. sp., the lateral margins of the carapace are slightly divergent posteriorly with the greatest width at the level of the posterolateral angles ( Figs. 1A , 2 A), whereas in C. dehaani the margins are subparallel and the greatest width of the carapace is across the midlength of the carapace ( Figs. 1 B, 6A). The operculum of the vulva is terminally subtruncate in C. magnus n. sp. ( Fig. 5 F) but is more rounded in C. dehaani ( Fig. 5 G). The new species attains a much larger adult size than in any known specimens of C. dehaani [maximum CW 52.2 mm (CBM-ZC 11452), 42.0 mm (CBM-ZC 11458) in C. dehaani ]. In live C. magnus n. sp., the carapace has a mottled pattern of black-brown and gray-brown or yellowish gray with scattered whitish spots; the carpus and the dorsal part of chela are light olive or yellowish gray; striae on the ambulatory meri are dark brown ( Fig. 1A )., There are no mottled patterns or whitish spots on the carapace of C. dehaani ; the carpus and the dorsal part of cheliped are dark, occasionally purplish to brown; and the striae on the ambulatory meri are not dark-coloured ( Fig. 1 B).

Sesarma hanseni Rathbun, 1897 , is clearly a junior subjective synonym of C. dehaani . The species was briefly described from one small (CW 16.5 mm) male supposedly from the West Indies ( Rathbun, 1897). Abele (1975), however, refigured the type and showed that the stated provenance was incorrect and that the specimen probably came from East Asia. The external features of the species as well as the male gonopod figured, particularly the structure of the terminal process ( Abele 1975: fig. 2B, C) leave no doubt that Sesarma hanseni Rathbun, 1897 , is conspecific with Chiromantes dehaani s. str.

Chiromantes neglectus has been regarded as a junior synonym of C. dehaani (see Tesch 1917), but Ng et al. (2001, 2008) remarked that this taxon is a valid species, although they did not elaborate. Since the present new species and C. dehaani are morphologically close, it is necessary to compare C. magnus n. sp. with C. neglectus . Topotypic specimens of C. neglectus from Shanghai, China, were examined. Chiromantes magnus n. sp. is easily distinguished from C. neglectus by many characters, most notable being the shape of the carapace and the proportionally longer ambulatory legs. In C. magnus n. sp., the anterolateral margins of the carapace are nearly straight and slightly diverging posteriorly ( Figs. 1A , 2 A) (nearly straight and almost parallel and slightly sinuous in C. neglectus , Fig. 6 B); the carapace is relatively less inflated with the dorsal surface less convex in C. magnus n. sp. ( Fig. 2 B); the median notch on the frontal margin is deeper in C. magnus n. sp. ( Figs. 1A , 2 A) than in C. neglectus ( Fig. 6 B); the grooves dividing the postfrontal ridges on the carapace are distinctly broader and deeper in C. magnus n. sp. ( Figs. 1A , 2 A) (cf. C. neglectus ; Fig. 6 B); the dorsal surface of the cheliped carpus is more strongly rugose and tuberculate in C. magnus n. sp.; the ambulatory legs are proportionately longer in C. magnus n. sp. ( Fig. 1A ) (cf. C. neglectus ; Fig. 6 B); the terminal process of the first gonopod of C. magnus n. sp. is slightly constricted at the base with the distal part broader ( Fig. 5C –E) (evenly cylindrical in C. neglectus ; Fig. 7 E, F); and the tip of the operculum of the first gonopod of C. magnus n. sp. is subtruncate ( Fig. 5 F) (rounded in C. neglectus like in C. dehaani ; Fig. 5 G). The colouration in life is also different in the two species, with the dorsal surface of the carapace more uniformly grey in C. neglectus .

There is no evidence that the true C. dehaani is present in the Ogasawara Is., and therefore all previous records of C. dehaani (see synonymy) from the Ogasawara Is. are here referred to C. magnus n. sp. Chiromantes magnus n. sp. is the sixth species of decapod crustaceans seemingly endemic to the islands., with C. dehaani its analogue on the Japanese mainland. The other five endemic species are Paratya boninensis Satake & Cai, 2005 (Caridea: Atyidae ) (Satake & Cai 2005); Palaemon ogasawaraensis Kato & Takeda, 1981 (Caridea: Palaemonidae ) ( Kato & Takeda 1981; Hayashi 2000); Panulirus brunneiflagellum Sekiguchi & George, 2005 (Achelata: Palinuridae ) ( Sekiguchi & George 2005); Pagurus insulae Asakura, 1991 (Anomura: Paguridae ) ( Asakura 1991; Komai 2003); and Eriocheir ogasawaraensis Komai, Yamasaki, Kobayashi, Yamamoto & Watanabe, 2006 (Brachyura: Varunidae ) ( Komai et al. 2006).

Figures

FIGURE 2. Chiromantes magnus n. sp., holotype, male (47.2 × 52.2 mm), CBM-ZC 11452. A, carapace and eyes, dorsal view; B, anterior part of carapace, anterior view.

FIGURE 3. Chiromantes magnus n. sp., holotype, male (47.2 × 52.2 mm), CBM-ZC 11452. A, entire animal in ventral view, showing coloration in life; B, carapace and abdomen, ventral view.

FIGURE 4. Chiromantes magnus n. sp., holotype, male (47.2 × 52.2 mm), CBM-ZC 11452. A, left cheliped, dorsal view; B, left chela, outer view.

FIGURE 5. A, C – E, Chiromantes magnus n. sp., paratype, male (45.5 × 50.3 mm), CBM-ZC 11457. B, F, C. magnus n. sp., paratype female (25.2 × 27.9 mm), CBM-ZC 11455. G, C. dehaani (H. Milne Edwards, 1853), female (24.1 × 27.0 mm), CBM- ZC 11458. A, male abdominal somite 6 and telson; B, female abdominal somite 6 and telson; C, left first gonopod; D, E, distal part of left first gonopod (denuded); F, G, left female gonopores. Scale bars: 5 mm for A – C; 1 mm for D – G.

FIGURE 1. A, Chiromantes magnus n. sp., holotype, male (47.2 × 52.2 mm), CBM-ZC 11452, entire animal in dorsal view. B, C. dehaani (H. Milne Edwards, 1853), male (37.7 x 42.0 mm), CBM-ZC 11458, entire animal in dorsal view. Showing coloration in life.

FIGURE 6. A, Chiromantes dehaani (H. Milne Edwards, 1835), lectotype, male (35.7 × 39.5 mm), RMNH. CRUS. D 157. B, C. neglectus (De Man, 1887), male (25.5 × 30.2 mm), CBM-ZC 11459 preserved in ethanol.

FIGURE 7. A – C, G Chiromantes dehaani (H. Milne Edwards, 1835), lectotype, male (35.7 × 39.5 mm), RMNH. CRUS. D 157. D – F, H, C. neglectus (De Man, 1887), male (31.8 × 35.6 mm), ZRC 1998.310. A, D, left male gonopods (denuded); B, C, E, F, distal part of left male gonopods (denuded); G, H, male abdominal somites 6 and telsons. Scale bars: 2 mm for A, D; 1 mm for B, C, E, F; 5 mm for G, H.