Promdam et al.: Nakhonsimon ramromensis gen. & sp. nov.
Taxonomy & Systematics
RAFFLES BULLETIN OF ZOOLOGY 62: 496–500

Date of publication: 11 July 2014
http://zoobank.org/urn:lsid:zoobank.org:pub:CFF0FE1E-ABC3-43BC-9DE5-5BCCB814645F

Nakhonsimon ramromensis, a new genus and species of freshwater
crab (Crustacea: Decapoda: Brachyura: Potamidae) from Nakhon Si
Thammarat, Peninsular Thailand
Rueangrit Promdam1, Jaruwat Nabhitabhata2* & Peter K. L. Ng3
Abstract. A new genus and species of potamid crab, Nakhonsimon ramromensis, is described from Nakhon SiThammarat, southern Thailand. The new genus resembles Stoliczia and Johora from Peninsular Thailand andMalaysia in general features, but can be distinguished by the form of the male thoracic sternites 3 and 4, and thestructure of the gonopods.
Key words. Nakhonsimon ramromensis, new genus, new species, Brachyura, Potamidae, freshwater crab, PeninsularThailand, taxonomy

INTRODUCTIONTAXONOMYSpecimens of an unusual potamid crab were recently collectedfrom Khao Ram Rome, Nakhon Si Thammarat, in southernThailand. Externally, this new species resembles membersof Stoliczia Bott, 1966, and Johora Bott, 1966, but theform of the male anterior thoracic sternites 3 and 4, and thestructure of the gonopod are sufficiently different to warrant
the establishment of a new genus for it.

Family Potamidae Ortmann, 1896
Subfamily Potamiscinae Bott, 1970
Nakhonsimon, new genus
Type species. Nakhonsimon ramromensis, new species,
designated herein.

The following abbreviations are used: G1, male first gonopod;
G2, male second gonopod. Measurements are given in
millimeters (mm) as carapace width × length. Terminology
used essentially follows Ng (1988). Thai words used in
the text are Khao [= Mountain], Amphoe [= District], andChangwat [= Province]. Specimens examined are deposited in
the reference collection of Princess Maha Chakri Sirindhorn
Natural History Museum, Faculty of Science, Prince ofSongkla University, Hat Yai, Thailand (PSUNHM); and the
Zoological Reference Collection of the Lee Kong Chian
Natural History Museum (ex Raffles Museum of Biodiversity
Research), National University of Singapore (ZRC).

Diagnosis. Dorsal carapace regions well demarcated;
anterolateral margins convex; epibranchial tooth low. Surfacesof carapace, chelipeds, and ambulatory legs with numerous
short stiff setae. Posterior margin of epistome with sharp
median triangle, lateral margins sinuous. Exopod of third
maxilliped extending beyond distal margin of ischium,reaching lower than half level of merus length, without
flagellum. Ambulatory legs relatively long, articles slender.
Male thoracic sternites 3, 4 separated by a distinct groove.
G1 distinctly curved; curvature mainly in slender, subterminal
segment; terminal segment straight, longer than half length ofsubterminal segment, spatuliform. G2 distal segment longer
than half length of basal segment.
Etymology. The name is an arbitrary combination of
Changwat (= Province) Nakhon Si Thammarat, the type
locality of the type species, in combination with the genus
name Potamon. Gender of genus neuter.

Department of Biology, Faculty of Science, Prince of Songkla University, Hatyai,
Songkhla 90112, Thailand

1Remarks. Nakhonsimon, new genus, appears to bemorphologically closest to Stoliczia Bott, 1966 (type species
Telphusa stoliczkana Wood-Mason, 1871) in the general shapeand structure of the carapace, and in having no flagellumon the exopod of the third maxilliped. Stoliczia contains
15 species and is distributed across the northern half ofPeninsular Malaysia to southern Thailand (Ng 1988, 1992b,1993, 2004; Ng et al., 2008), Nakhonsimon, however, differs

Excellence Centre for Biodiversity of Peninsular Thailand (CBIPT), Faculty ofScience, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand; Email:jaruwat.n5@gmail.com, jaruwat.n@psu.ac.th (*corresponding author)

23
Lee Kong Chian Natural History Museum, National University of Singapore, 14
Science Drive 4, Singapore 117543, Republic of Singapore; Email: peterng@nus.edu.sg© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)

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39A, 51A, 52A, 54A; Naiyanetr, 2001: fig. 1D; Brandis,
2002: fig. 16; Yeo & Ng, 2007: 280).

in several important respects, viz. male thoracic sternites 3and 4 are separated by a distinct groove (Fig. 1C) (versus notvisible in Stoliczia, with thoracic sternites 3 and 4 completely
fused to each other); the relatively longer ambulatory merus(ratio of length of last ambulatory merus to median length ofcarapace, 0.60, versus 0.43‒0.59 in Stoliczia species) (Fig.
1A); and the strongly curved G1 subterminal segment which
has the distal portion slender (Fig. 2B, C) (versus straighter
subterminal segment of G1 with the distal portion relatively
broader, gradually tapering distally in Stoliczia) (cf. Ng,
1988: figs. 24–36; Ng, 1992b: figs. 4A–E, pl. 3 fig. A; Ng,
1993: figs. 3A, C–F, 4A–E, 5A, C–F, pl. 3 fig. A, pl. 4 fig.
A; 2004: fig. 8J).

Nakhonsimon ramromensis, new species(Figs. 1‒4)
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, 2December 2011.

Paratypes: —1 male (17.8 × 14.4 mm) (PSUNHM 211514333-0006), 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, 10April 2012; 1 male (20.8 × 16.2 mm) (ZRC 2013.0692),

Johora Bott, 1966, which occurs from southern Thailand toSingapore, is also morphologically similar to Nakhonsimon
in general shape and structure of the carapace. The G1s ofJohora species, however, are never as strongly curved (cf.
Ng 1987, 1988, 1990). Johara also differs from Nakhonsimonin possessing a distinct flagellum on the exopod of thethird maxilliped, and having no visible groove between
the male thoracic sternites 3 and 4 (cf. Ng, 1988: figs.
13–23; 2004: figs. 7G–K; Yeo, 2001: figs. 1A–C, F, 2C–F;
Leelawathanagoon et al., 2005: figs. 1, 2A, B, D–F).
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 themale thoracic sternites 3 and 4 (versus not visible); and thestrongly curved G1 with a proportionately long terminal
segment, (about half length of subterminal segment) andlacking 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), anda 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, andThaipotamon by the complete absence of a flagellum on
the exopod of the third maxillipeds. In Phaibulamon, theexopod of the third maxilliped is even shorter, just reaching
the distal edge of the ischium (versus distinctly beyond thedistal 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,Fig. 1. Nakhonsimon ramromensis, new genus and species, holotype,male, 31.8 × 24.6 mm, PSUNHM 211514-333-0005. A, dorsal
view; B, frontal view; C, ventral view.

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Promdam et al.: Nakhonsimon ramromensis gen. & sp. nov.
stream from Lalana Waterfall, Khao Ram Rome, AmphoeRon Phibun, Changwat Nakhon Si Thammarat, PeninsularThailand, coll. R. Promdam, 10 April 2012.

subdistal spine on inner angle. Merus without subterminalspine.
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 whenmeasured dorsally. Propodus slightly longer than carpus.
Merus without distinct subdistal spine. Lower margin of
ambulatory merus, propodus, dactylus with scattered short
stiff setae.

Description of male holotype. Carapace (Fig. 1A) squarish;dorsal surfaces relatively flat, regions distinct, almost
glabrous except for scattered short, stiff setae, lateral regionswith distinct oblique striae, cervical grooves distinct, verybroad, shallow, reaching deep H-shaped central depression.
Anterolateral margins arcuate, crested, lined with blunt
granules, appearing gently serrated, clearly separated fromdistinctly converging posterolateral margins. Frontal margin
gently deflexed, straight, not clearly separated from supraorbital margin; epibranchial tooth low, separated fromexternal 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 welldeveloped, corneal pigmentation well developed, distinct.
Sub-orbital, sub-branchial, pterygostomial regions (Fig.
1B) rugose. Outer surfaces of epistome (between anterior,posterior margins), pterygostomial regions hirsute. Anterior
margin of epistome (Fig. 1B) almost straight, parallel withfrontal margin; posterior margin with one median triangular
tooth, lateral margins sinuous.

Suture between thoracic sternites 2, 3 (Fig. 1C) distinct,
very gently convex (towards buccal field). Thoracic sternites
3, 4 separated by a distinct groove, extending from baseof 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) 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)long, slender; flagellum long, forming circular curve, aslong as basal segment.

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

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 aresimilar to the male holotype in nearly all respects. The vulvae,Chelipeds (Fig. 1A) unequal, right larger, fingers of bothchelae distinctly longer than palm. Outer surfaces of allarticles rugose. Carpus with robust, obliquely directedFig. 2. Nakhonsimon ramromensis, new genus and species, holotype, male, 31.8 × 24.6 mm, PSUNHM 211514-333-0005. A, left third
maxilliped; B, ventral view of left G1; C, dorsal view of left G1; D, left G2. Scale bars = 2.0 mm.

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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.

however, are relatively large, eliptical in shape, without
operculums; positioned on anterior half of sternite 6 (Fig. 3).
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).

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

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

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 adjacentareas as well.
ACKNOWLEDGEMENTS

Colour. Dirty brown to dark gray on all dorsal aspects (Fig.
1). 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 halfof the palm, and the entire pollex are orange. The tips offingers are beige-coloured. The integument at the articulations
between the carpus and merus of the chelipeds is bright red(Figs. 1C, 4).

We would like to thank Pakhon Thaweephol, staff of Channel
7 television broadcasting stations, Nakhon Si Thammarat,
who first introduced this unusual crab to us and helpedwith transportation and accommodations. Thanks arealso to Pongrat Dumrongrojwattana and Sararat Tanamai,
Department of Biology, Prince of Songkla University;and Siriwat Dangsri, staff of Ron Phibun Hospital, whohelped in the field trips. We gratefully acknowledge ourreviewers, Darren Yeo, Tohru Naruse and Jose Christopher E.
Mendoza for their helpful suggestions and comments, whichhave improved the manuscript. We also thank staff of theExcellence Centre for Biodiversity of Peninsular Thailand,
Department of Biology; and Princess Maha Chakri Sirindhorn
Natural History Museum, Faculty of Science, Prince ofSongkla University for their assistance in the laboratorywork. This work was supported by the Higher Education
Research Promotion and National Research University Projectof Thailand, Office of the Higher Education Commission.
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Fig. 3. Vulvae position of Nakhonsimon ramromensis, new genus
and species, paratype, female, 17.8 × 14.4 mm, PSUNHM 211514333-0006. Scale bar = 2.0 mm

Fig. 4. Live coloration of Nakhonsimon ramromensis, new genus
and new species, holotype, male, 31.8 × 24.6 mm, PSUNHM
211514-333-0005.

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