Nakhonsimon ramromensis, Promdam & Nabhitabhata & Ng, 2014

Promdam, Rueangrit, Nabhitabhata, Jaruwat & Ng, Peter K. L., 2014, Nakhonsimon ramromensis, a new genus and species of freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from Nakhon Si Thammarat, Peninsular Thailand, Raffles Bulletin of Zoology 62, pp. 496-500 : 497-499

publication ID	https://doi.org/ 10.5281/zenodo.5354303
publication LSID	lsid:zoobank.org:pub:CFF0FE1E-ABC3-43BC-9DE5-5BCCB814645F
persistent identifier	https://treatment.plazi.org/id/03F7235E-FFF7-FFBE-FC5B-E2780AC2FD5E
treatment provided by	Tatiana
scientific name	Nakhonsimon ramromensis
status	sp. nov.

Treatment

Nakhonsimon ramromensis View in CoL , new species

( Figs. 1 ‒ 4 View Fig View Fig View Fig View Fig )

Material examined. Holotype: male (31.8 × 24.6 mm) ( PSUNHM 211514-333 - 0005 ), Channel 7 television broadcasting stations, Khao Ram Rome , ca. 996 m asl, Amphoe Ron Phibun , Changwat Nakhon Si Thammarat, Peninsular Thailand, coll. R. Promdam, 2 December 2011.

Paratypes: — 1 male (17.8 × 14.4 mm) ( PSUNHM 211514- 333-0006), stream from Lalana Waterfall, Khao Ram Rome, Amphoe Ron Phibun, Changwat Nakhon Si Thammarat, southern Thailand, coll. R. Promdam, 26 December 2011; 1 female (16.7 × 13.4 mm), 1 juvenile (13.0 × 10.7 mm) ( PSUNHM 211514-333-0007), stream from Lalana Waterfall, Khao Ram Rome, Amphoe Ron Phibun, Changwat Nakhon Si Thammarat, Peninsular Thailand, coll. R. Promdam, 10 April 2012; 1 male (20.8 × 16.2 mm) ( ZRC 2013.0692), Another terrestrial potamid genus known from southern Thailand, Terrapotamon Ng, 1986 , also lacks a flagellum on the exopod of the third maxilliped, and has relatively long, slender ambulatory legs with slender dactyli. Nakhonsimon , however, can be distinguished from Terrapotamon by its distinctly lower carapace (ratio of carapace width to height 2.2, versus 1.6 in Terrapotamon ); the merus of the third maxilliped being more squarish (versus more elongate, i.e., longer than wide); the presence of a groove between the male thoracic sternites 3 and 4 (versus not visible); and the strongly curved G1 with a proportionately long terminal segment, (about half length of subterminal segment) and lacking the large prominent swelling along margins (versus gently curved, with a proportionately short terminal segment (about 0.22 ‒ 0.37 times length of subterminal segment), and a distinct subdistal swelling on the outer margin between terminal and subterminal segments) (cf. Ng, 1988: fig. 37C; Ng & Naiyanetr, 1998: figs. 1C–F, F–I; Leelawathanagoon et al., 2010: figs. 1C, D, F–I, 2C, 3)

Other Thai potamid genera that have visible sutures or grooves between the male thoracic sternites 3 and 4 are Beccumon Yeo & Ng, 2007 ; Phaibulamon Ng, 1992a ; Takpotamon Brandis, 2002 ; and Thaipotamon Ng & Naiyanetr, 1993 . Nakhonsimon is readily differentiated from Beccumon , Takpotamon , and Thaipotamon by the complete absence of a flagellum on the exopod of the third maxillipeds. In Phaibulamon , the exopod of the third maxilliped is even shorter, just reaching the distal edge of the ischium (versus distinctly beyond the distal edge of the ischium in Nakhonsimon ). In any case, the G1 structures of these four genera are very different from that of Nakhonsimon in that the subterminal segment does not bend outwards (cf. Ng, 1992a: figs. 1, 2A, B; Ng & Naiyanetr, 1993: figs. 4C, 5C, 16C, 17C, 20C, 37A, 38A, stream from Lalana Waterfall, Khao Ram Rome, Amphoe Ron Phibun, Changwat Nakhon Si Thammarat, Peninsular Thailand, coll. R. Promdam, 10 April 2012.

Description of male holotype. Carapace ( Fig. 1A View Fig ) squarish; dorsal surfaces relatively flat, regions distinct, almost glabrous except for scattered short, stiff setae, lateral regions with distinct oblique striae, cervical grooves distinct, very broad, shallow, reaching deep H-shaped central depression. Anterolateral margins arcuate, crested, lined with blunt granules, appearing gently serrated, clearly separated from distinctly converging posterolateral margins. Frontal margin gently deflexed, straight, not clearly separated from supraorbital margin; epibranchial tooth low, separated from external orbital angle by distinct cleft; external orbital angle broadly triangular, outer margin straight, gently serrated, twice as long as inner margin. Epigastric cristae distinct, rugose, not sharp, slightly anterior of postorbital cristae, clearly separated by broad groove. Orbits large, eyes well developed, corneal pigmentation well developed, distinct. Sub-orbital, sub-branchial, pterygostomial regions ( Fig. 1B View Fig ) rugose. Outer surfaces of epistome (between anterior, posterior margins), pterygostomial regions hirsute. Anterior margin of epistome ( Fig. 1B View Fig ) almost straight, parallel with frontal margin; posterior margin with one median triangular tooth, lateral margins sinuous.

Exopod of third maxilliped ( Fig. 2A View Fig ) extending beyond distal margin of ischium, reaching lower than half level of merus length, without trace of flagellum. Ischium with deep median groove. Merus squarish, cristate along margins.

Chelipeds ( Fig. 1A View Fig ) unequal, right larger, fingers of both chelae distinctly longer than palm. Outer surfaces of all articles rugose. Carpus with robust, obliquely directed

subdistal spine on inner angle. Merus without subterminal spine.

Ambulatory legs relatively long, slender, second leg longest, last leg shortest; surfaces of all articles rugose, dorsal margin gently serrated. Dactylus of first leg about 8 times as long as high. Dactylus length about 1.4 times that of propodus when measured dorsally. Propodus slightly longer than carpus. Merus without distinct subdistal spine. Lower margin of ambulatory merus, propodus, dactylus with scattered short stiff setae.

Suture between thoracic sternites 2, 3 ( Fig. 1C View Fig ) distinct, very gently convex (towards buccal field). Thoracic sternites 3, 4 separated by a distinct groove, extending from base of chelipeds to tip of margin of sternoabdominal cavity. Thoracic sternite 8 completely separated by longitudinal median line, lacking transverse ridge. Press button abdominal locking mechanism on sternite 5, knob-like, small. Abdomen triangular; telson subequal in length to somite 6, lateral margins weakly concave, tip rounded; somite 1 reaches base of last pair of legs; somites 2 ‒ 6 progressively broader, longer anteriorly.

Male gonopores coxal. G1 ( Fig. 2B, C View Fig ) terminal segment clearly separated from subterminal segment about 0.5 times length, straight, long, without dorsal flap, tip rounded; distal portion of subterminal segment bent, slender. G2 ( Fig. 2D View Fig ) long, slender; flagellum long, forming circular curve, as long as basal segment.

Female characters. The paratype female (16.7 × 13.4 mm) is still immature, with the abdomen not completely covering the anterior thoracic sternum. The non-sexual characters are similar to the male holotype in nearly all respects. The vulvae, however, are relatively large, eliptical in shape, without operculums; positioned on anterior half of sternite 6 ( Fig. 3 View Fig ).

Etymology. The species is named after the type locality, Khao Ram Rome.

Remarks. The characters that distinguish Nakhonsimon ramromensis from the superficially similar species of Stoliczia and Johora have already been discussed (see earlier).

Some characters of Nakhonsimon ramromensis vary with increasing size. In a relatively smaller specimen (20.8 × 16.2 mm, ZRC 2013.0692), the epibranchial tooth is indistinct and not clearly separated from the external orbital angle; and the G1 subterminal segment is slightly straighter.

Colour. Dirty brown to dark gray on all dorsal aspects ( Fig. 1 View Fig ). Ventral surfaces of carapace are pale orange. Proximal lateral of ambulatory legs are light orange. Lower oblique two thirds of the dactylus of chelipeds, lower oblique half of the palm, and the entire pollex are orange. The tips of fingers are beige-coloured. The integument at the articulations between the carpus and merus of the chelipeds is bright red ( Figs. 1C View Fig , 4 View Fig ).

Habitat. Adults of this species appear to be completely terrestrial, as they were found far away from any permanent water sources; the holotype male was found in a temporary pool on the highest point of the mountain ridge (about 996 m above sea level). Smaller crabs were observed in a phyotelm on a tree trunk that grows near the stream. Most juveniles were found beneath rocks in the main stream.

The gecarcinucid Phricotelphusa aedes ( Kemp, 1923) was collected in the same vicinity as Nakhonsimon ramromensis .

Distribution. So far only known from the type locality on Khao Ram Rome, Changwat Nakhon Si Thammarat, Peninsular Thailand, but can probably be found in adjacent areas as well.