RAFFLES BULLETIN OF ZOOLOGY 2020
Taxonomy & Systematics
RAFFLES BULLETIN OF ZOOLOGY 68: 529–538

Date of publication: 23 June 2020
DOI: 10.26107/RBZ-2020-0069
http://zoobank.org/urn:lsid:zoobank.org:pub:FC02AE31-5C72-4A83-B061-113D42E04850

Indawmon thanayei, a new genus and new species of freshwater crab
(Crustacea: Brachyura: Potamidae) from Indawgyi Lake, Kachin
State, Myanmar
Peter K. L. Ng1, Win Mar2 & Hsi-Te Shih3*
Abstract. A new genus and new species of potamid crab, Indawmon thanayei, is described from Indawgyi Lake in
Kachin State, Myanmar. The taxon is characterised mainly by its male first gonopod structure which has the terminaland subterminal segments not clearly demarcated, with the terminal segment subcylindrical in shape, graduallytapering to a sharp tip and is bent at an angle of about 45–90°. The new genus is compared with Indochinamon
and Shanphusa, which it superficially resembles. The genetic data (based on the mitochondrial 16S rDNA) also
supports the establishment of the new taxa.
Key words. new genus, new species, Indawmon thanayei, Myanmar, mitochondrial 16S rDNA, morphology

INTRODUCTION

Museum, National University of Singapore. The abbreviations
G1 and G2 are used for the male first and second gonopods,
respectively. Measurements provided (in millimetres) are of
the maximum carapace width and length, respectively. The
terminology follows Ng (1988) and Davie et al. (2015).

Indawgyi Lake in Kachin State, northern Myanmar, isa tectonic lake and one of the largest in Southeast Asia.
Measuring approximately 24 by 13 km, it is also the largest
inland lake in Myanmar. The lake and its surrounding habitats
have a rich fauna, and not surprisingly, many of its freshwater
inhabitants are endemic. Its fish fauna has been the subjectof many studies (e.g., Prashad & Mukerji, 1929; Kottelat,
2015, 2017a, b; Ng & Kottelat, 2018) and there is even an
endemic newt (Zaw et al., 2019) present.

In total, 72 species of the Potamidae are included in themolecular analysis, with sequences of 68 species derived from
Shih et al. (2009) and Shih & Ng (2011). Four additional
species are added for the present study: Indawmon thanayei,
new species (holotype, ZRC 2019.1032, and two paratypes,
ZRC 2019.1033), Inlethelphusa acanthica (Kemp, 1918)(ZRC 2018.1370; Inle Lake, Myanmar), Shanphusa ywarngan
Ng & Whitten, 2017 (holotype, ZRC 2016.0171; Ywangan,
Myanmar), and Doimon maehongsonense (Naiyanetr,
1992) (paratype, ZRC 1991.1848–1849; Mae Hong Son,
Thailand). Sequences of 16S were obtained following
Shih et al. (2009), using the primers 16H10 and 16L29(Schubart, 2009) and aligned with the aid of MUSCLE
function of MEGA (version 10.0.5; Kumar et al., 2018),
after verification with the complementary strand. Sequencesof different haplotypes have been deposited in the DNA
Data Bank of Japan (DDBJ). To establish the systematic
position of the taxa, the 16S sequences of genera from theeastern Asian continent in Shih et al. (2009), Huang et al.
(2014, 2016, 2017a, b, 2018), and Wang et al. (2019), areincluded for comparison. We followed Shih et al. (2009) to
exclude the variable regions in loop regions of the 16S that
could not be aligned adequately for phylogenetic analyses.
The best-fitting model for sequence evolution of the 16S
dataset was determined by PartitionFinder (version 2.1.1;
Lanfear et al., 2017), selected by the Bayesian information
criterion (BIC). The best model obtained was GTR+I+G,
which was subsequently applied for Bayesian inference(BI) analysis. The BI analysis was performed with MrBayes(version 3.2.2; Ronquist et al., 2012) and the search was

Surprisingly, no freshwater crab has ever been reported
from this ecosystem before. Recent collections obtained aseries of specimens from streams flowing into the lake. On
the basis of the morphological and genetic data, they prove
to belong to a new genus and new species, here named
Indawmon thanayei.
MATERIAL AND METHODS
The material examined is deposited in the Zoological
Reference Collection (ZRC), Lee Kong Chian Natural History

Accepted by: Jose Christopher E. Mendoza
Lee Kong Chian Natural History Museum, 2 Conservatory Drive, National Universityof Singapore, Singapore 117377, Republic of Singapore. Email: peterng@nus.edu.sg

1

Department of Zoology, Mandalay University of Distance Education, Republic of
the Union of Myanmar. Email: winmar1328@gmail.com

2

Department of Life Science and Research Center for Global Change Biology,
National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan.
Email: htshih@dragon.nchu.edu.tw (*corresponding author)

3© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)529

Ng et al.: New genus and species of freshwater crab from Myanmar
run with four chains for 10 million generations, with trees
sampled every 1,000 generations. The convergence of chains
was determined by the average standard deviation of split
frequency values below the recommended 0.01 (Ronquist
et al., 2005) and the first 1,500 trees were discarded as theburnin accordingly. ML analysis was conducted in RAxML(version 7.2.6; Stamatakis, 2006). The model GTR + G (i.e.,
GTRGAMMA) was used for all subsets with 100 runs andfound the best ML tree by comparing likelihood scores. The
robustness of the ML tree was evaluated by 1,000 bootstrap
pseudoreplicates under the model GTRGAMMA.
TAXONOMYFamily Potamidae Ortmann, 1896
Subfamily Potamiscinae Bott, 1970 sensu Yeo & Ng,
2004
Indawmon, new genus
Type species. Indawmon thanayei, new species, by present
designation and monotypy.
Fig. 1. Indawmon thanayei, new genus, new species, paratype male
(27.6 × 21.9 mm) (ZRC 2019.1033), colour in life. A, fronto-dorsal
view; B, ventral view.

Diagnosis. Adult carapace transversely ovate; epigastriccristae anterior to postorbital cristae; postorbital cristae notreaching anterolateral margin; anterolateral margin cristate,lined with low granules; third maxilliped with slender
exopod with long flagellum; male pleon broadly triangular;
male thoracic sternites 3 and 4 longitudinally elongate,with sternopleonal cavity reaching only to imaginary line
connecting proximal edge of coxae of chelipeds; press-button
tubercle of male sternopleonal locking mechanism laterally
flattened, distal part distinctly chitinised; G1 subterminal
segment tapering gradually from broad base, distal part notprominently narrow; G1 terminal and subterminal segments
not clearly demarcated; without visible suture or any feature
separating segments in ventral view; barely visible area
between segments slightly less chitinised; terminal segment
subcylindrical, gradually tapering to sharp tip, bent at angleof about 45–90° from longitudinal axis; G2 longer than G1;
vulvae large with chitinised dorsal rim.

terminal and subterminal segments are distinctly separated
by a suture, clearly visible in ventral view and indicated bysutures or less chitinised sections in dorsal view (see Yeo &Ng, 2007). In Indawmon, there is no clear suture separating
the terminal and subterminal segments in ventral view (Fig.
6B, F). In dorsal view, there is an area between the twosegments that appear to be less chitinised but this is only
barely visible (Fig. 6C, G).
The G1 of Indawmon superficially resembles that ofInlethelphusa Yeo & Ng, 2007, in that the terminal segment iselongate. Inlethelphusa is endemic to Lake Inle and adjacentareas (see Kemp, 1918; Yeo & Ng, 2007; Ng et al., 2020).
Indawmon, however, differs from Inlethelphusa in having
the anterolateral margin lined with low granules (Figs. 2,
3A–D) (versus anterolateral margin lined with many sharp
teeth in Inlethelphusa; cf. Ng et al., 2020: fig. 6A, B); theG1 subterminal segment tapering gradually from the broadbase, the distal part not being prominently narrow and not
clearly demarcated from the subcylindrical terminal segment
which ends in a sharp tip (Fig. 6A–C, E–G) (versus distal
part of G1 subterminal segment narrows abruptly from broadbase, narrow and clearly demarcated from cylindrical terminal
segment which ends in a truncate tip in Inlethelphusa; cf.
Ng et al., 2020: fig. 6D, E); and male thoracic sternites 3
and 4 being longitudinally elongate, with the sternopleonalcavity reaching only to an imaginary line connecting theproximal edge of the coxae of the chelipeds (Fig. 3E, G,H) (versus male thoracic sternites 3 and 4 proportionately
longitudinally shorter with sternopleonal cavity reaching toimaginary line connecting middle part of coxae of chelipeds

Etymology. The name is derived from the name of thelake, Indawgyi, in arbitrary combination with the endingof “Potamon”. Gender neuter.
Remarks. The general carapace features of Indawmon, newgenus, are typical of many potamid genera and have few
diagnostic features. In Myanmar, the carapace shape, surface
features, structure of the epigastric and postorbital cristae,
and armature anterolateral margin of Indawmon resemble
those of genera like Indochinamon Yeo & Ng, 2007, andShanphusa Yeo & Ng, 2007. Their G1 structures, however,differ markedly.
One of the diagnostic features of Indawmon is that theterminal and subterminal segments are not well demarcated.
In almost all potamiscines (and many potamines), the530RAFFLES BULLETIN OF ZOOLOGY 2020

Fig. 2. Indawmon thanayei, new genus, new species. Dorsal habitus. A, holotype male (27.8 × 22.9 mm) (ZRC 2019.1032); B, paratypemale (27.6 × 21.9 mm) (ZRC 2019.1033); C, paratype male (19.7 × 16.5 mm) (ZRC 2019.1033); D, paratype female (32.2 × 24.6 mm)(ZRC 2019.1033).

in Inlethelphusa; cf. Ng et al., 2020: fig. 6C). Also noteworthy
is that the press-button tubercle in Indawmon is unusual inthat it is laterally flattened, while in most potamiscines, it isrounded or peg-like (e.g., in Inlethelphusa, Ng et al., 2020:
fig. 4J). Compared to Inlethelphusa, the vulva of Indawmon
is directed obliquely and anteriorly with a distinct posteriorrim (Fig. 5D) (versus vulva directed more laterally with alarge lateral rim; cf. Ng et al., 2020: fig. 7B). The genetic
data also supports their separation (see Discussion below).

smoother; lateral parts of anterolateral and branchial regions
covered with numerous prominent, flattened to uneven
granules; mesogastric, urogastric, cardiac and intestinal
regions weakly rugose but not granular; suborbital, subhepaticand sub-branchial regions almost smooth; pterygostomial
region with low, flattened granules (Fig. 4A). Epigastriccristae prominent, strongly rugose, not distinctly cristate,separated by narrow, median Y-shaped furrow; epigastriccristae anterior to postorbital cristae, separated from it byshort furrow; postorbital cristae distinct, margin uneven,prominently raised, lined with striae but not distinctly
cristate, subparallel to frontal margin, outer edge low, with
granules less prominent (Fig. 3A). Cervical grooves distinct,
not deep, relatively narrow, not reaching lateral margins,connected to H-shaped median gastric groove (Fig. 3A).
Frontal margin almost straight, appearing gently sinuousin frontal and dorsal views (Figs. 3A, 4A). External orbital
tooth distinct, triangular, outer margin almost twice length of
inner margin, demarcated from rest of anterolateral marginby small but distinct V-shaped cleft; epibranchial tooth small,
sharp (Figs. 2A, 3A). Anterolateral margins convex, cristate,lined with low but distinct granules, appearing gently serrated(Fig. 3A). Posterolateral margin gently sinuous, converging
towards gently convex posterior carapace margin (Fig. 3A).
Orbits subovate; eye filling orbital space; eye peduncle
relatively short, stout; cornea large, round, pigmented (Figs.
3A, 4A). Supraorbital margin gently sinuous, entire (Fig.
3A). Suborbital margin concave, complete, lined with low
granules; inner angle with low tooth (Fig. 4A). Antennae
short, stretching across base of eyes; antennules short, folding

Indawmon thanayei, new species(Figs. 1–5)
Material examined. Holotype male (27.8 × 22.9 mm)(ZRC 2019.1032), Nant Tae and Wai Lone streams, flowing
into southern entrance of Indawgyi Lake, 24°56′52.8″N96°20′09.6″E, Mohnyin Township, Kachin State, Myanmar,
coll. Than Aye, 2018. Paratypes: 4 males (27.7 × 22.3 mm,
27.6 × 21.9 mm, 23.0 × 18.3 mm, 19.7 × 16.5 mm), 4 females(32.7 × 25.4 mm, 32.2 × 24.6 mm, 25.3 × 20.3 mm, 23.2 ×
19.2 mm) (ZRC 2019.1033), same data as holotype.
Diagnosis. As for genus.
Description of male holotype. Carapace transversely ovatein adults, distinctly wider than long (width-to-length ratio
1.21); dorsal surface gently convex from frontal view,
glabrous, regions not prominently inflated, appearing almost
flat in frontal view, appears glabrous (Figs. 2A, 3A, 4A).
Frontal regions with flattened granules, postorbital regions531

Ng et al.: New genus and species of freshwater crab from Myanmar

Fig. 3. Indawmon thanayei, new genus, new species. A, E, F, holotype male (27.8 × 22.9 mm) (ZRC 2019.1032); B, G, paratype male
(27.6 × 21.9 mm) (ZRC 2019.1033); C, H, paratype male (19.7 × 16.5 mm) (ZRC 2019.1033). A­–D, dorsal view of carapace; E, G, H,
anterior thoracic sternum and pleon; F, anterior thoracic sternum and sternopleonal cavity.

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Fig. 4. Indawmon thanayei, new genus, new species. A–D, holotype male (27.8 × 22.9 mm) (ZRC 2019.1032); E, paratype male (27.6
× 21.9 mm) (ZRC 2019.1033); F, paratype male (19.7 × 16.5 mm) (ZRC 2019.1033). A, frontal view of cephalothorax; B, left third
maxilliped; C, outer view of chelae; D–F, male pleon (F slightly deformed).

transversely in rectangular fossa (Fig. 4A). Posterior marginof epistome with distinct median triangle, lateral margin
sinuous (Fig. 4A).

of carpus rugose, inner distal angle with large sharp toothand small sub-basal tubercle (Fig. 2A). Outer surfaces ofchelae rugose, dorsal surface appears squamose with larger,
strongly flattened granules (Fig. 4C). Fingers of major chela
short, stout, gently curved, subequal to length of palm, outersurface of both fingers lined with two rows of pits; dorsal
margin of dactylus with 5–7 low tubercles, proximal one
largest, sharp; cutting edges of both fingers with variously
sized sharp teeth and denticles; dorsal margin of dactylus
with low tubercles and granules (Fig. 4C). Fingers of minor
chela similar to major chela in form (Fig. 4C).

Third maxillipeds covering most of buccal cavity whenclosed; ischium subrectangular, with distinct oblique mediangroove, surface mostly smooth with scattered pits and shortsetae; merus subquadrate, slightly wider than long, surface
rugose, margins cristate, anteroexternal angle rounded;
exopod slender, reaching to about one-third length of merus,
with elongate flagellum that reaches across width of merus(Fig. 4B).

Ambulatory legs short, articles relatively stout; second pairlongest, last pair shortest (Fig. 2A). Merus short, stout, outersurface gently rugose, dorsal margin uneven, subcristate,
without subdistal spine or tooth; carpus rugose, dorsal
margin cristate, outer surface with low submedian crista on
first to third legs, that on fourth leg smooth; dorsal margin

Chelipeds asymmetrical, right larger (Fig. 2A). Anterior
margin of basis-ischium lined with several small low granules;
ventral margins of merus lined with prominent low sharp
granules, with tubercle on subdistal surface, dorsal margin
uneven, appearing weakly serrated (Fig. 3E). Outer surface533

Ng et al.: New genus and species of freshwater crab from Myanmar

Fig. 5. Indawmon thanayei, new genus, new species. A, B, holotype male (27.8 × 22.9 mm) (ZRC 2019.1032); C, D, paratype female(32.2 × 24.6 mm) (ZRC 2019.1033). A, male sternopleonal cavity and G1; B, penis; C, female pleon and thoracic sternum; D, female
sternopleonal cavity and vulvae. Abbreviations: cx4 and cx5, coxae of third and fourth ambulatory legs, respectively; pe, penis; pt, pressbutton tubercle of pleonal locking mechanism; st4–st8, sternites 4–8, respectively; vu, vulvae.

of propodus with crista, outer surface with low, submediancrista; dactylus relatively short, gently curved, quadrate incross section, margins with short, sharp pectinate spines with
dense, very short setae that do not obscure margins (Fig. 2A).

G1 relatively slender; subterminal segment widest basally,
gradually tapering towards terminal segment, groove for G2
ventral, with prominent subdistal angle on gently concave
outer margin, just before terminal segment; subterminal
segment not distinctly separated from terminal segment by
groove or other structure in ventral view, in dorsal view,
poorly defined area of weaker chitinisation marks demarcation
between segments; terminal segment long, subcylindrical,
no dorsal flap, gently tapering, tip sharp, bent at angle ofabout about 45° from the longitudinal axis (Fig. 6A–C). G2
elongate, longer than G1; basal segment longer than distalsegment (Fig. 6D).

Thoracic sternum, notably sternites 3 and 4, as long as broad,surface almost smooth (Fig. 3E). Sternites 1, 2 completely
fused to form broadly triangular plate; separated from sternite
3 by distinct, gently concave suture (towards buccal cavity);sternites 3, 4 completely fused without discernible groove
or suture (Fig. 3E). Sutures 4/5, 5/6, 6/7, and 7/8 mediallyinterrupted; median longitudinal groove on sternites 7 and
8 (Fig. 5A). Penis coxal, on condyle of coxa of fourth
ambulatory leg (Fig. 5B). Sternopleonal cavity deep, reaching
imaginary line connecting posterior edges of cheliped coxae(Fig. 3E). Sternite 8 not visible when pleon closed. Male
press-button pleonal locking mechanism composed of distinct
laterally flattened tubercle with distal part distinctly chitinised,
positioned on posterior third of sternite 5 (Fig. 5A).

Females. Ambulatory meri of female specimens (Fig.
2D) proportionately shorter than those of males. Pleon
longitudinally ovate in adults, covering most of thoracic
sternum with all somites and telson free (Fig. 5C). Vulva
large, positioned on anterior margin of sternite 6, directed
obliquely and anteriorly; posterior part with weakly calcified
rim (Fig. 5D).

Pleon broadly triangular, all somites and telson free;telson triangular, lateral margins gently concave; somite
6 transversely trapezoidal, much wider than long, lateral
margin gently concave; somites 3–5 trapezoidal, gradually
decreasing in width, increasing in length; somite 3 widest;
somites 1 and 2 subrectangular, very wide, reaching to basesof coxae of fourth ambulatory legs (Figs. 3E, 4D).

Variation. The carapace form varies slightly in this species.
Adult specimens have a transversely ovate carapace withthe anterolateral surfaces prominently granulated, theposterolateral surfaces with distinct striae, and the epigastricand postorbital cristae lined with strong striae and granules.
The degree of this granulation, however, varies slightly (Fig.
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Fig. 6. Indawmon thanayei, new genus, new species. A–D, holotype male (27.8 × 22.9 mm) (ZRC 2019.1032); E–G, paratype male (27.6
× 21.9 mm) (ZRC 2019.1033); H, paratype male (19.7 × 16.5 mm) (ZRC 2019.1033). A, E, H, left G1 (ventral view); B, F, distal partof left G1 (ventral view); C, G, left G1 (dorsal view); D, left G2. Scales: A, D, E, H = 1.0 mm; B, C, F, G = 0.5 mm.

3A, B). Smaller specimens have a slightly more quadrate
carapace with the granules and striae lower and less prominent(Fig. 3C). The granules lining the anterolateral margins arealso relatively smaller in smaller specimens (Fig. 3C). In
the large specimens (e.g., the females exceeding 30 mm incarapace width), the carapace is proportionately wider, withthe granules and striae also relatively weaker (Fig. 3D).

Most of the adult G1 terminal segments, including that of
the holotype, are bent at an angle of about 45° from thelongitudinal axis (Fig. 6A–C). One adult paratype male
(27.6 × 21.9 mm, ZRC 2019.1033), however, is unusualin that the G1 terminal segment (both left and right sides)
is bent at an angle of almost 90° (Fig. 6E–G). This malespecimen is also unusual in that the male pleon (especiallysomites 3 and 5) is also slightly wider proportionately (Fig.
4E). These differences must be considered as variation as it
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Ng et al.: New genus and species of freshwater crab from Myanmar

Geothelphusa olea (W Taiwan) AB428455
Geothelphusa fulva (Ryukyus) AB428456
0.82/57
Geothelphusa albogilva (S Taiwan) AB127366
BI / ML
Candidiopotamon rathbunae (W Taiwan) AB208598
1/98
Ryukyum yaeyamense (Ryukyus) AB428458
support values
Amamiku amamense (Ryukyus) AB428457
0.6/Sinolapotamon anacoluthon (Hong Kong) AB428453
0.94
Yarepotamon gracilipa (Guangxi, SW China) AB428452/50
Qianguimon rongxianense (Guangxi, SW China) MK335483
0.05
Minutomon shanweiense (Guangdong, S China) LC176065
1/100
Chinapotamon glabrum (Guangxi, SW China) AB428451
0.95
Chinapotamon cf. longlinense (Guangxi, SW China) LC198521/62
Diyutamon cereum (Guizhou, SW China) LC198519
0.98/1/100 Nanhaipotamon formosensis (W Taiwan) AB212867
Nanhaipotamon nanriense (Fujian, SE China) AB212868
1/92
Huananpotamon angulatum (Fujian, SE China) AB428454
Minutomon shanweiense (Guangdong, S China) LC176065
0.64/0.76
Cantopotamon hengqinense (Guangdong, S China) LC342047
1/89 /66
Cantopotamon shangchuanense (Guangdong, S China) LC342048
0.55
Cantopotamon zhuhaiense (Guangdong, S China) LC342046/0.59/Cantopotamon yangxiense (Guangdong, S China) LC342050
0.74/Luteomon spinapodum (Guangdong, S China) LC383796
1/100
Tiwaripotamon xiurenense (Guangxi, SW China) LC198522
Tiwaripotamon edostilus (Haiphong, N Vietnam) LC198523
0.72/- 1/92
Neotiwaripotamon jianfengense (Hainan, S China) AB428460
Hainanpotamon fuchengense (Hainan, S China) AB428461
0.6/Apotamonautes hainanensis (Hainan, S China) AB428459
Megapleonum ehuangzhang (Guangdong, S China) LC383794
Megacephalomon kittikooni (Laos) AB428462
Indochina II
Esanpotamon namsom (Thailand) AB428463
0.8/50Beccumon jarujini (Thailand) AB428479
0.94/60
1/99
Potamiscus yiwuensis (Yunnan,China) AB428476
Pupamon nayung (Thailand) AB428477
Inlethelphusa acanthica (Myanmar) MT586286
Indochinamon ou (Laos) AB428481
Indochinamon tannanti (Yunnan, SW China) AB428482
1/97
Shanphusa curtobates (Myanmar) AB428478
Indawmon thanayei (x3) (Myanmar) MT586285
1/100 Shanphusa ywarngan (Myanmar) MT586287
0.96/Doimon maehongsonense (Thailand) MT586288
0.89/59
Kanpotamon
duangkhaei (Thailand) AB428471
0.97/56
Flabellamon sp. (Thailand) AB428472
Tomaculamon pygmaeus (Thailand) AB428473
1/99
Thaiphusa sp. (Thailand) AB428474
0.76/Demanietta renongensis (Thailand) AB428475
1/80
Mindoron balssi (Mindoro, N Philippines) AB428464
N Philippines
Ovitamon artifrons (Luzon, N Philippines) AB428466
1/99 Eosamon smithianum (Thailand) AB428486
0.82/68
Eosamon boonyaratae (Thailand) AB428487
1/91
Kukrimon cucphuongense (N Vietnam) AB428483
Indochina I
1/Pudaengon sakonnakorn (Thailand) AB428484
0.5/Eosamon yotdomense (Thailand) AB428485
1/99
Longpotamon planum (Anhui, E China) AB428469
Longpotamon baiyanense (Hunan, C China) AB428470
0.83/59
Tenuilapotamon latilum (Hubei, C China) AB428468
1/87
Daipotamon minos (Guizhou, SW China) LC198524
China
0.92
Mediapotamon leishanense (Guizhou, SW China) LC155164/62
Sinopotamon davidi (Shaanxi, C China) LC155132
Parapotamon spinescens (Yunnan, SW China) AB428467
1/Yuebeipotamon calciatilis (Guangdong, S China) LC176064
S China
0.75/Semicirculara lincangensis (Yunnan, SW China) MH045059
New genus 2 loshingense (Sichuan, SW China) AB428488
0.67/Potamiscus yongshengense (Yunnan, SW China) KY963597
New genus 1 aff. yunnanense (Yunnan, SW China) AB290629
Trichopotamon daliense (Yunnan, SW China) AB428492
0.55/SW China
Pararanguna semilunatum (Yunnan, SW China) AB428490
Artopotamon latopeos (Yunnan, SW China) MH045061
1/100
Arquatopotamon jizushanense (Yunnan, SW China) KY963596
Tenuipotamon huaningense (Yunnan, SW China) AB428491
Aparapotamon grahami (Yunnan, SW China) AB428489
1/100
Johora johorensis (Johor, W Malaysia) AB290620
Malay Peninsula
Johora murphyi (Johore, W Malaysia) AB290621
Socotrapotamon nojidensis (Socotra, Yemen) AB428493‘Socotra’
1/100

China—East Asia Islands

Indochina—SW China

Fig. 7. A Bayesian inference (BI) tree of 16S rDNA for subfamily Potamiscinae, with sequences and accession numbers in Shih et al.
(2009) and some additional species (see Material and Methods). Species in Myanmar highlighted in grey. Probability values at nodes
represent support values for BI and maximum likelihood (ML). Only values >50% shown.

536

RAFFLES BULLETIN OF ZOOLOGY 2020
agrees with the other paratypes in almost all other aspects,
and genetically, they all share the same haplotype (Fig. 7).
Subadult males (e.g., smallest paratype male 19.7 × 16.5mm, ZRC 2019.1033) have proportionately narrower pleons(Fig. 4F) and the G1 is only weakly chitinised, not strongly
setose, and its terminal segment is less bent, being at anangle of only 30° (Fig. 6H).

DISCUSSION
The establishment of the genus Indawmon, new genus, ismainly based on the unique character of the G1 morphology,
which is supported by the 16S rDNA evidence (Fig. 7).
Genetically, this genus is closely related with other genera
from Myanmar, Thailand, Laos, and southwestern China(Shih et al., 2009; Huang et al., 2016, 2017a, b, in press).

Colour. In life, the carapace is yellowish-brown overall,with the ventral surfaces pale yellow (Fig. 1).

The genetic data (Fig. 7) indicates that Shanphusa isprobably not monophyletic, with the two tested species, S.
curtobates (Kemp, 1918) and S. ywarngan Ng & Whitten,
2017, coming out in different clades. This is supported bymorphology and the three species of Shanphusa can bedivided into two groups. One group includes the type species
S. browneana (Kemp, 1918) and S. ywarngan; while thesecond group contains S. curtobates. Shanphusa curtobates
differs from S. browneana and S. ywarngan in having a
relatively higher carapace which is more ovate, with theanterolateral margin markedly convex (Ng & Whitten, 2017:
fig. 4B); the ambulatory merus is proportionately shorter
and wider (Ng & Whitten, 2017: fig. 4B); the male pleon
is proportionately broader (Ng & Whitten, 2017: fig. 4C);
and the G1 subterminal segment is distinctly stouter (Ng &Whitten, 2017: fig. 4D). In contrast, in S. browneana and S.
ywarngan, the carapace is lower, more quadrate in shape withthe anterolateral margin gently convex (Yeo & Ng, 2007:
fig. 12A, B; Ng & Whitten, 2017: figs. 1A, B, 2A, 4A);
the ambulatory meri are proportionately more slender andelongate (Yeo & Ng, 2007: fig. 12A; Ng & Whitten, 2017:
figs. 1A, 4A); the male pleon is more slender (Yeo & Ng,
2007: fig. 12C; Ng & Whitten, 2017: fig. 2D–F); and theG1 subterminal segment is more slender (Yeo & Ng, 2007:
fig. 12D, E; Ng & Whitten, 2017: fig. 3A–C). Shanphusa
curtobates will probably need to be separated to its own
genus at a later date but fresh specimens of S. browneana
should be collected, re-examined, and its genetics determined
before such an action is taken. The present material of S.
browneana could not be used for the molecular analysis.

Etymology. The species is named after the collector, Mr.
Than Aye, an Assistant Lecturer in the Department of
Zoology, Yadanabon University, Myanmar.
Remarks. The variation in the G1 structure observed in
one of the larger males (27.6 × 21.9 mm, ZRC 2019.1033)
is noteworthy as it is significant, and if locality data wereabsent and genetic data not available, one would easily
have treated it as a separate species. Not only were bothleft and right G1s of the same form, the pleon was alsoslightly wider. There is no doubt, however, that they are
all conspecific, with all other morphological characters
agreeing and the genetic data confirms this (Fig. 7). It is
becoming increasingly clear that there is more variation in
the G1 morphology of many Asian potamids than previously
recorded, and the use of this character to differentiate species
must be more carefully scrutinised, especially if specimens
are from the same drainage and/or are of different sizes(e.g., see Indochinamon khinpyae; cf. Ng & Win Mar, 2018).
Habitat. The specimens were collected from two highland
streams, about 16 km upstream from their entrance into thesouthern portion of Indawgyi Lake. The substrate of thestreams is rocky, with the water shallow but fast-flowing(Than Aye, pers. comm.).
Conservation. A large number of freshwater crab species
in the Indo-Burma area are still listed in the IUCN Red
List as “data deficient” (Cumberlidge et al., 2009, 2012),
and that of Indawmon thanayei, new species, is not very
different. As far as recent collections are concerned andfrom the observations of the collector, the crab is not rarein Indawgyi, and as such we suggest the category of Least
Concern for the time being.

In any case, the taxonomy of Shanphusa, Indochinamon, andDoimon will need to be reappraised as the composition ofthese genera is far from ideal, and has already been suggested
in other studies (see Shih et al., 2009; Shih & Ng, 2011;
Ng & Win Mar, 2018).

Distribution. Known only from Indawgyi Lake, Kachin
State, Myanmar.

ACKNOWLEDGEMENTS

Molecular analyses. In the phylogenetic tree (Fig. 7),
Indawmon, new genus, comes out in a highly supported
clade together with the genera from Myanmar, Thailand,Laos, and Yunnan in southwestern China, which belong
to the “Indochina–SW China” group (Shih et al., 2009).
Those Myanmar genera include Indawmon, Inlethelphusa,
Shanphusa, and Doimon. Noteworthy in this genetic tree
is that Shanphusa ywarngan Ng & Whitten, 2017, from
Myanmar comes out in a separate clade with Doimon
maehongsonense (Naiyanetr, 1992) from Thailand withhigh support.

This study was partially supported by a grant from the Ministryof Science and Technology (MOST 108-2313-B-005-007MY3), Executive Yuan, Taiwan, to HTS. We acknowledge
the kind help of Chao Huang as well as an anonymousreferee who helped improve the manuscript.
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