Parasesarma gecko n. sp.

(Figs. 4–6, 19B, 20A, 21B, 22A, 23A, 24B, 25E)

Sesarma leptosoma, De Man 1889: 436, pl. 10, fig. 11.—Ortmann 1894: 725. Not Parasesarma leptosoma (Hilgendorf, 1869) .

Parasesarma aff. leptosoma, Nakasone 1977: 10, 11.—Nishidaira 1980: 66.

Sesarma (Parasesarma) leptosoma, McLay & Ryan 1990: 115, table 2. Not Parasesarma leptosoma (Hilgendorf, 1869) .

Parasesarma leptosoma, Takeda & Nunomura 1976: 86 .— Davie 2002: 223.—Shokita et al. 2002: 78. —Shokita et al. 2003: 102.—Rahayu & Ng 2009: 35.— Koller et al. 2010: 359.— Naruse 2010: 51.— Maenosono & Naruse 2015: 13, figs. 2E, 6, 11E, F.— Maenosono & Saeki 2016: 8, table 1. Not Parasesarma leptosoma (Hilgendorf, 1869) .

Material examined. HOLOTYPE: male (16.2× 14.6 mm) (RUMF-ZC-4710), Japan: Okinawa Island: Awase (on Kandelia obovata Sheue, Liu & Yong), 18 July 2016, J.- J. Li . PARATYPES: 1 male (14.5× 12.3 mm) (ZRC 2008.0501), Guam: near Pago Bay, August 2001, H.- C. Liu. —1 male (14.4× 12.6 mm), 1 female (12.5×11.0 mm) (ZRC 2008.1252), Japan: Miyako Island: Shimajiri, 20 March 2001, P.K.L. Ng. —1 male (15.9× 13.7 mm), 1 female (15.3×13.0 mm) (ASIZ 73381) Japan: Yaeyama Islands: Iriomote Island, 17 September 2004, H.- C. Liu. — 3 males (13.0× 11.3 mm, 12.5×11.0 mm, 10.4×9.0 mm), 1 female (10.1× 8.5 mm), 1 ovigerous female (11.9×10.3) (NMNS-7779-001), Japan: Okinawa Island: Awase, 18 July 2016, J.- J. Li. — 5 males (17.0× 15.1 mm, 16.9× 15.1 mm, 15.9× 14.3 mm, 15.5× 13.7 mm, 13.4×12.0 mm), 1 ovigerous female (11.8×9.9) (NMNS-7779-003), Japan: Okinawa Island: Awase, 19 July 2016, J.- J. Li. — 2 males (16.6× 14.4 mm, 15.6× 14.1 mm) (NMNS-7779-004), Japan: Okinawa Islands: Yagaji Island, 20 July 2016, J.- J. Li. — 1 female (11.7×9.7) (RUMF-ZC-2898), Japan: Okinawa Island: Nago: Oura River, 13 April 2010, T. Naruse. — 2 males (13.4× 11.4 mm, 10.6× 8.9 mm) (RUMF- ZC-2899), Japan: Okinawa Island: Nago: Oura River, 4 June 2010, T. Naruse. — 1 male (14.8× 12.5 mm) (RUMF- ZC-2900), Japan: Okinawa Islands: Yagaji Island: Gabu, 9 June 2010, T. Naruse. —1 male (12.3×10.0 mm), 1 female (10.8× 8.3 mm) (RUMF-ZC-2901), Japan: Okinawa Island: Kin: Okukubi River, 8 February 2014, T. Naruse. — 1 male (15.9× 13.9 mm) (RUMF-ZC-2902), Japan: Miyako Island: Kawamitsu, 18 February 2014, T. Naruse. — 1 male (16.9×14.5) (RUMF-ZC-2903), Japan: Okinawa Islands: Yagaji Island: Gabu, 9 March 2010, Naruse. —2 males (17.4×14.7, 15.5×13.0 mm), 1 female (16.5× 14.3 mm) (RUMF-ZC-2930), Japan: Yaeyama Islands: Iriomote Island: Utara River, 4 May 2014, Naruse. — 3 males (1.7× 12.4 mm, 13.4×12.0 mm, 10.9× 9.5 mm), 1 ovigerous female (15.6× 13.8 mm) (RUMF-ZC-4711), Japan: Okinawa Island: Awase, 17 July 2016, J.- J. Li. —1 ovigerous female (20.2×17.5) (NMNS-7779-002) (leg variation), Japan : Okinawa Island: Awase, 18 July 2016, J.- J. Li. Other material : 5 males (19.1× 16.6 mm, 14.9× 13.3 mm, 13.7× 11.5 mm, 12.9×11.0 mm, 12.4× 10.4 mm), 4 ovigerous females (18.1× 15.4 mm, 16.8× 14.8 mm, 16.5× 14.2 mm, 16.2× 14.1 mm) (NMNS-7779-006), Guam, September 2008, H.-C. Liu. —1 male (13.3× 11.5 mm) (ZRC 2017.196), Vanuatu: West Baldwin Cove, Nasouli River mouth intertidal, hard bottom, Expédition SANTO 2006, station VM4, intertidal area near mangroves, 15°34.9'S 167°01.8'E, 11 September 2006, P.K.L. Ng et al ..— 1 adult female (13.2× 11.5 mm) , 2 juvenile females (8.9× 7.6 mm, 8.6× 7.2 mm) (ZRC 2017.197), Vanuatu: Belmoul lagoon channel, intertidal, sand and muddy sand, Expédition SANTO 2006, station VM9, intertidal area near mangroves, 15°35.8'S 167°06.2'E, 13 September 2006, P.K.L. Ng et al.

Diagnosis. Carapace (Figs. 4A, E, G, I, 5A, 22A) squarish in general outline, 1.2 times broader than long; regions well defined, separated by shallow grooves; postfrontal region distinct, separated into 4 lobes by deep grooves; front deflexed downwards (Figs. 4C), margin slightly concave in dorsal view; lateral margin straight, subparallel along most of length before curving to join almost straight posterior carapace margin; cornea extending or just reaching tip of external orbital tooth (Figs. 4A, E, G, I, 5A, 22A). Ischium of third maxilliped with shallow median sulcus, merus with distinct submedian ridge; exopod slender, tip reaching half-length of outer margin of merus, flagellum long. Male cheliped palm with 2 (sometimes 3) transverse pectinate crests (11–13 and 3–10 corneous teeth, respectively) (Figs. 5B, C, 6A–C) on upper surface; upper surface of dactylus with 10–15 (mostly 11) symmetrical, obliquely elongate dactylar tubercles, proximal 1–5 tubercles steep, sharp, other tubercles large but becoming lower distally, distalmost tubercle indistinct (Figs. 5C, 6D–F, 19B). Ambulatory legs relatively stout for this species-complex, P3 and P4 about 1.7 times carapace width; P3 and P4 coxae without dense setae; P3 merus 2.5 times as long as broad; P3 propodus 4.8 times as long as broad; P3 dactylus 0.4 times length of propodus (Fig. 20A). G1 relatively slender (Figs. 5D–G, 21B), slightly bent; apical process corneous, elongated, slightly bent at angle of 45°, long, stout, ending in rounded tip (Figs. 5D–G, 21B). G2 short, less than quarter length of G1 (Fig. 21B).

Morphological variation. Several male specimens have asymmetrical chelipeds (Figs. 4I, J), probably due to regeneration of lost limbs. The dactylar tubercles of the male chela ranges from 10 to 15 (average 11) (Figs. 6D–F). The corneous teeth of the proximal transverse pectinate crest on the male cheliped palm varies from 3 to 10 (Figs. 6A–C).

Colour in life. Carapace dark brown, mottled with darker and lighter blotches; chelipeds brownish orange, but more yellowish in large males; ambulatory legs brown (Figs. 22A, 23A, 24B, 25E).

Remarks. Parasesarma gecko n. sp. most closely resembles P. macaco n. sp. in having yellowish chela in life and the relatively slender G1, but it can be distinguished from the latter by the number of dactylar tubercles on the male chela (10–15 in P. gecko n. sp. versus 6–8 in P. macaco n. sp.). The other differentiating characters are summarized in Table 1.

The sizes of ovigerous females of P. gecko n. sp. show substantial disparity (the smallest carapace width is 11.8 mm and the largest is 20.2 mm), but no other obvious morphological variation detected between small and large specimens. The cheliped asymmetry in P. gecko n. sp. is common in males (Figs. 4I, J). Other than the asymmetry, the dactylar tubercles and the proximal pectinate crest on the palm vary substantially from 10–15 and 3–10, respectively. Such wide range of variation has not been observed in other species of this complex. We also found a female with malformed ambulatory legs (Figs. 4G, H). The variations might result from the tendency of P. gecko n. sp. to automise its chelipeds and ambulatory legs more readily compared to other species we have observed (see “Ecology”). There are several records from Japan referred to P. leptosoma . Nakasone (1977) first recorded “ P. aff. leptosoma ” from Gesaji River, Okinawa Island, and noted that the crabs often climb on the mangrove aerial roots and leaves. Nishidaira (1980: 66) also recorded P. aff. leptosoma from Ishigaki and Iriomote Islands. Shokita (2002) first formally recorded P. leptosoma from Oura River, Okinawa Island, and later from Sakagawa River, Okinawa Island (Shokita 2003). Recently, Maenosono & Naruse (2015) reported P. leptosoma from the Ryukyu Islands, and concluded that the “ P. aff. leptosoma ” (listed by Nakasone (1977) and Nishidaira (1980) and P. leptosoma represent the same species. Our study has shown that only P. gecko n. sp. occurs in the Ryukyu Islands, and consequently, the previous records of P. leptosoma from the area are all referred to this new species.

De Man (1889), Ortmann (1894) and McLay & Ryan (1990) reported Sesarma leptosoma from Fiji Island. De Man (1889) ’s illustrations (pl. 10 Fig. 11) show the shape of frontal border of the carapace in the dorsal view is distinctly concave, but this feature is not observed in the true P. leptosoma from Africa. The morphology of this Fijian material instead matches that of P. gecko n. sp. which is known for certain from Japan, Guam and Vanuatu. Davie (2002) recorded material from Queensland, Australia, and on the basis of geography, his record is probably P. gecko n. sp. Takeda & Nunomura (1976) listed P. leptosoma from New Caledonia based on two females, and although no figure was provided, this record falls inside the range of P. gecko n. sp., and as such, their record is also referred to this species.

Etymology. The specific epithet alludes to the new species’ quick movements on vertical surfaces and its tendency to autotomise its appendages when handled, as also observed in the eponymous lizard. The name is used here as a noun in apposition.

Distribution. Japan: Okinawa Island, Miyako Island, Ishigaki Island, Iriomote Island (Nakasone 1977; Nishidaira 1980; Shokita 2002, 2003; Koller et al. 2010; Naruse 2010; Maenosono & Naruse 2015; Maenosono & Saeki 2016); Guam (Rahayu & Ng 2009), Queensland, Australia (Davie 2002); Fiji (De Man 1889; Ortmann 1894; McLay & Ryan 1990), New Caledonia (Takeda & Nunomura 1976) and Vanuatu (present study).

Ecology. In Okinawa Island, Parasesarma gecko n. sp. is common on the mangrove trees Kandelia obovata Sheue, Liu & Yong, Pandanus odoratissimus Linn., as well as on rocks and man-made vertical structures (e.g. cement and pillars) (Fig. 25E) near estuarine waters (Maenosono & Naruse 2015; Maenosono & Saeki 2016). It was found together with Metopograpsus latifrons (White, 1847) (Grapsidae) in the same habitat (Okinawa Island, Japan) (present paper). The new species is active during day and night time, moves fast between mangrove roots, branches or other vertical surfaces. Parasesarma gecko n. sp. tends to lose its appendages very readily when captured, apparently more so than P. kui n. sp., P. macaco n. sp. from Taiwan and P. tarantula n. sp. from Sulawesi.