Demanietta sunthorni, Lheknim & Leelawathanagoon & Ng, 2023

Lheknim, Vachira, Leelawathanagoon, P. & Ng, Peter K. L., 2023, Demanietta sunthorni, a new species of freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from Adang-Rawi Island Group, Andaman Sea, south Thailand, Raffles Bulletin of Zoology 71, pp. 377-386 : 378-384

Demanietta sunthorni , new species

( Figs. 2–6 )

Material examined. Thailand: off Satun Province, Adang Island, Langu District : holotype: male (36.6 × 27.7 mm) ( ZRC 2022.0826 ) , unnamed creek, Ao Dan, south of Adang Island , 6°30.732′N 99°18.226′E, 35 m amsl, coll. V. Lheknim & P. Leelawathanagoon, 20 October 2008 . Paratypes: 1 male (33.5 × 26.3 mm), 1 female (38.5 × 29.4 mm) ( PSUZC 20081020 - 01.01 ) , 1 male (18.2 × 15.5 mm), 1 female (33.2 × 26.4 mm) ( ZRC 2022.0827 ) , same as holotype; 2 males (27.3 × 21.2 mm, 35.1 × 26.7 mm) ( ZRC 2022.0828 ) , 2 males (25.9 × 19.7 mm, 36.1 × 27.6 mm) ( PSUZC 20081023 - 01.01 ) , Klong Samed Daeng, NE of Adang Island in the vicinity of Ban Ko Adang, Ao Talo Lae Lae , 6°32.987′N 99°18.780′E, 50 m amsl, coll. V. Lheknim & P. Leelawathanagoon, 23 October 2008 .

Comparative material. Demanietta khirikhan Yeo, Naiyanetr & Ng, 1999: 1 male (PSUZC- 20041126 -01.01), unnamed creek in karst sinkhole NE of Rajjaprabha Reservoir,

Tapi River Basin, Ban Khao Phang, Ban Ta Khun District, Surat Thani Province, 9°5.4960′N 98°41.9810′E, 60 m amsl, Thailand, coll. V. Lheknim & P. Leelawathanagoon, 26 November 2004. Demanietta nakhonsi Yeo, Naiyanetr & Ng, 1999: 1 male (52.3 × 39.4 mm) ( PSUZC 20020922 - 01.02 ), stream around CH7 Telecommunication Station , Khao Ram Rom, Ron Phibon District, Nakhon Sri Thammarath Province, Thailand, 8°14.320′N 99°48.850′E, 920 m amsl, coll. V. Lheknim & P. Leelawathanagoon, 22 September 2002; 1 male (45.1 × 34.9 mm) ( PSUZC 20020614 - 02.05 ), stream at Lalana Waterfall , Khao Ram Rom, Ron Phibon District, Nakhon Sri Thammarath Province, Thailand, 8°13.450′N 99°48.310′E, 365 m amsl, coll. V. Lheknim & P. Leelawathanagoon, 14 June 2002 ; 1 male (36.8 × 27.5 mm) ( PSUZC 20020616 - 05.01 ), stream at Namtok Yong , Klong Yong , Trang River Basin , Ban Sai Yai , Thung Song District, Nakhon Sri Thammarath Province, Thailand, 8°10.205′N 99°44.175′E, 105 m amsl, coll. V. Lheknim & P. Leelawathanagoon, 16 June 2002 [ Topotype ]. Demanietta renongensis ( Rathbun, 1904) : 1 male (45.3 × 34.1 mm) ( PSUZC 19870310 - 01.01 ), Klong Had Som Pan , upper western river basin, Muang Ranong District, Ranong Province, 9°51.059′N 98°41.617′E, 15 m amsl, Thailand, coll. V. Lheknim & P. Leelawathanagoon, 10 March 1987 ; 1 female (52.9 × 40.9 mm) ( PSUZC 19980423 - 05.03 ), Nam Tok Ngao , Ban Ngao, Muang Ranong District, Ranong Province, 9°51.341′N 98°37.745′E, 45 m amsl, Thailand, coll. V. Lheknim & P. Leelawathanagoon, 23 April 1998 ; 2 males (40.4 × 31.3 mm, 50.9 × 40.3 mm) ( PSUZC 20010520 - 05.11 ), Klong Bang Yang , Lung Suan river basin, Ban Bang Yang, Patao District, Chumphon Province, 9°45.171′N 98°40.667′E, 140 m amsl, Thailand, coll. V. Lheknim & P. Leelawathanagoon, 20 May 2001 ; 1 male (31.0 × 21.0 mm), 1 female (44.9 × 33.4 mm) ( PSUZC 20010521 - 06.06 ), Klong Kapao , Klong Tha Taphao river basin, Ban Yai- Tai, Tha Sae District, Chumphon Province, 10°44.625′N 99°12.494′E, 140 m amsl, Thailand, coll. V. Lheknim & P. Leelawathanagoon, 2 May 2001 ; 2 males (25.8 × 20.6 mm, 35.9 × 26.4 mm) ( PSUZC 20060902 - 05.03 ), Nam Tok Pak Cham , Trang River Basin , Ban Pak Cham, Huey Yod District, Trang Province, 7°44.919′N 99°41.701′E, 382 m amsl, Thailand, coll. V. Lheknim & P. Leelawathanagoon, 2 September 2006 .

Diagnosis. Carapace subquadrate, width to length ratio 1.26– 1.32; dorsal surface relatively low, not inflated; frontal region with numerous blunt granules ( Figs. 2 , 3A–D ); epigastric cristae clearly demarcated, area with mix of granules and rows of transverse striae; postorbital cristae distinct, sharp, separated from epigastric cristae by distinct gap; postorbital cristae joining epibranchial tooth by uneven granulated ridge; external orbital tooth triangular with outer margin longer than inner margin, clearly separated from epibranchial tooth by small cleft; epibranchial tooth distinct, triangular ( Fig. 3B ); posterior part of anterolateral region and posterolateral region with distinct transverse striae; subhepatic, suborbital and pterygostomial regions with distinct striae and granules ( Fig. 3C ); posterior margin of epistome with distinct acutely triangular median tooth ( Fig. 3C, D ); third maxilliped ischium subrectangular, approximately 1.7 times longer than wide ( Fig. 3E ); pleonal locking tubercle on median part of sternite 5 ( Fig. 5A ); male telson triangular with lateral margins concave ( Fig. 4C, D ); G1 slender, sinuous ( Fig. 6A, B ); subterminal segment relatively slender, with basal part not wide, gradually tapering to neck-like structure just before it joins terminal segment, with concavity on inner margin ( Fig. 6A, B ); terminal segment about 0.35 times length of subterminal segment (from ventral view), relatively long, sinuous, strongly bent at angle of 90–100° to longitudinal axis of subterminal segment, with broad semicircular dorsal fold, extending to tip of terminal segment, distal part distinctly curved upwards, sharply tapered towards sharp tip ( Fig. 6C, D ); G2 relatively long, longer than G1 ( Fig. 6E ).

Description of male holotype. Carapace subquadrate, width to length ratio 1.32; anterior half wider than posterior half, slightly convex, dorsal surface relatively low, not inflated, smooth except for frontal and lateral regions ( Figs. 2 , 3A, B ); frontal region with numerous blunt granules ( Fig. 3B–D ); epigastric cristae clearly demarcated, area with mix of granules and rows of transverse striae, medially separated by distinct V-shaped furrow; postorbital cristae distinct, sharp, separated from epigastric cristae by distinct gaps; postorbital cristae joining epibranchial tooth by uneven granulated ridge; external orbital tooth triangular with outer margin longer than inner margin, clearly separated from epibranchial tooth by small cleft; epibranchial tooth distinct, triangular ( Fig. 3B ); anterolateral margins strongly convex, serrate, lateral serrae distinct; anterior part of anterolateral region with some disperse granules, posterior part of anterolateral region with distinct transverse striae; posterolateral margins sinuous, convergent posteriorly ( Figs. 3A, B ); branchial, gastric and cardiac regions almost smooth, slightly convex, not distinctly inflated ( Fig. 3B, C ); orbital region with dispersed granules ( Fig. 3C ); subhepatic, suborbital and pterygostomial regions with distinct striae and granules ( Fig. 3C ). Cervical grooves distinct, relatively broad, joining prominent H-shaped median gastric groove ( Fig. 3B ). Frontal margin divided into 2 broad, subtruncate lobes, separated by shallow concavity; margin of each lobe slightly convex, separated from supraorbital margin by distinct rounded angle ( Fig. 3B ). Orbits subovate in anterior view; eye filling most of orbital space; eye short, peduncle stout; cornea large, pigmented ( Fig. 3B, C ). Supraorbital margins distinctly concave at inner margin, entire, lined with round granules ( Fig. 3B ). Suborbital margins concave, complete, lined with round granules ( Fig. 3C ). Posterior margin of epistome gently sinuous, with distinct acutely triangular median tooth, lateral margins with small submedian fissure ( Fig. 3C, D ).

Third maxilliped covering most of buccal cavity when closed; ischium subrectangular, approximately 1.7 times longer than wide, with distinct longitudinal submedian sulcus, subparallel to inner margin; merus subquadrate with anterior margin slightly projecting medially, anteroexternal angle rounded, wider than long, with concave outer surface, surface slightly rugose; exopod relatively slender with prominent anterointernal margin tooth, reaching beyond upper edge of ischium, to approximately one-third length of merus, with distinct flagellum that is subequal to or as long as width of merus, about one-third exopod length ( Fig. 3E ).

Cheliped slightly asymmetrical, relatively stout, outer surface covered with low tubercles, with larger tubercles especially on upper parts ( Figs. 3A , 4A ); fingers gently curved, gaping, relatively longer than palm; posterodorsal margin of dactylus serrate, outer surface with 2 long rows of pits, outer surface of pollex with 2 long rows of pits, cutting edges of both fingers with various sized teeth and denticles; carpus with sharp spine on inner angle, with low basal spiniform tubercle below main spine, outer surface of distal part distinctly rugose, granulated, with proximal transverse striae ( Figs. 3A , 4A ); merus with 2 rows of sharp tubercles, upper margin with progressively larger tubercles, subdistal margin with low spines, outer surface of merus covered with low transverse striae; anterior margin of ischium with prominent sharp tubercles; basal part smooth.

Ambulatory legs not elongated, second pair longest, last pair shortest ( Fig. 3A ). Outer surface of merus relatively smooth with low transverse striae, dorsal margin slightly serrate, subdistal angle distinct, without distal tooth; carpus nearly smooth with low transverse striae, dorsal margin subcristate, outer surface of carpus of ambulatory legs 1–3 with distinct submedian ridge, absent on that of ambulatory leg 4; propodus with low transverse striae, both dorsal and ventral ridges lined with small sharp spines; dactylus lightly curved, compress in cross section, dorsal ridge covered with row of short sharp spines ( Figs. 3A , 4B ).

Thoracic sternum relatively narrow transversely, surface slightly pitted but smooth with lateral margins slightly setose ( Fig. 4C ). Sternites 1, 2 completely fused to form triangular plate, lateral margin distinctly convex, separated from sternite 3 by deep, sinuous, complete suture, median part shallower ( Fig. 4C ); sternites 3 and 4 completely fused except for lateral suture ( Fig. 4C ). Sternopleonal cavity reaching to imaginary line connecting median point of coxae of chelipeds ( Figs. 4C , 5A ); pleonal locking tubercle low, rounded, on median part of sternite 5 ( Fig. 5A ).

Pleon triangular, all somites and telson free, surface slightly pitted but smooth ( Fig. 4C, D ); somites 1, 2 subrectangular, wide, sinuous medially, reaching to bases of coxae of fourth ambulatory legs; somites 1 and 2, 2 and 3 separated by deep, sinuous groove medially; somites 3–6 trapezoidal, gradually convergent, lateral margin setose; somite 6 with length more than half width, lateral margins gently convex; telson triangular with rounded tip, lateral margin concave; sternite 8 not visible when pleon closed ( Fig. 4C, D ).

G1 slender, sinuous, inner margin and groove for G2 lined with setae ( Fig. 6A, B ); subterminal segment relatively slender, with basal part not wide, gradually tapering to neck-like structure just before it joins terminal segment, with concavity on outer margin ( Fig. 6A, B ); terminal segment clearly separated from subterminal segment by suture; terminal segment about 0.35 times length of subterminal segment (from ventral view), relatively long, sinuous, strongly bent at angle of 90–100° to longitudinal axis of subterminal segment, with broad semicircular dorsal fold, extending to tip of terminal segment, distal part distinctly curved upwards, sharply tapered towards tip, tip sharp ( Fig. 6C, D ). G2 long, longer than G1, distal segment about 0.75 times length of basal segment ( Fig. 6E ).

Variation and females. The smaller paratype male specimens agree very well with the holotype male, including in the structure of the G1. The smallest male (18.2 × 15.5 mm, ZRC 2022.0827) is a subadult, and while the gonopods are visible, they are poorly developed, being soft and without the dorsal flap. The female paratypes (PSUZC 20081020 - 01.01, ZRC 2022.0827) are adults and slightly larger than the male holotype. Their carapace, however, is relatively broader, CW/CL = 1.3, like that of the male paratype and subquadrate in general shape. Females have proportionately smaller and subequal chelipeds. The female pleonal somites and telson are longitudinally ovate in shape and cover most of the thoracic sternum except for lateral edges when closed; their pleonal somite 1 is the shortest, with somites 2–5 progressively longer; pleonal somite 6 is the longest, much broader than long, subequal in length to the telson, with the convex lateral margins. The female telson is broadly triangular, much broader than long, with convex lateral margins and narrow apex. The vulva is crescent-shaped, large, occupying two-thirds of the posterior two-thirds of sternite 5, pushing prominently into suture with sternite 6, opening large, directed obliquely inwards towards median line of sternum, without operculum or vulvar cover, vulvae positioned close to each other ( Fig. 5B ).

Life colouration. The cephalothorax is dark purple; the frontal margin, supra- and infraorbital margins, epibranchial tooth and postorbital crista are reddish brown; the chelipeds are generally reddish brown with the upper surface dark purplish-brown, the tips of the spines on the chelipeds are reddish brown; and the ambulatory legs are purple ( Fig. 2 ).

Etymology. The species is named after the late Assoc. Prof. Sunthorn Sotthibandhu, an eminent entomologist of the Biology Department, Faculty of Science, Prince of Songkla University (PSU). He used to be the head of the Department of Biology, as well as PSU President, and President of Songkhla Rajabhat University. The first author has known Ajarn Sunthorn for nearly 40 years, since he was an undergraduate student in his class. He was the first one who taught the first author the beauty of science and how it works. He has been an excellent colleague and a wonderful collaborator on teaching and science, and the many insightful discussions with him will be missed. After his retirement, he continued with research on the philosophy of science and kept working on this topic to his last day. He will be sorely missed. The specific epithet is derived from his first name, Sunthorn.

Remarks. Ng (2018: 189) noted that the species of Demanietta can easily be placed into two groups. One group has the epibranchial tooth large and prominent, and the epigastric and postorbital cristae are very sharp and confluent; while the other group has a low epibranchial tooth that is almost confluent with the rest of the margin and the epigastric and postorbital cristae are separated by a short groove (see also Yeo et al., 1999: 532). Demanietta sunthorni , new species, belongs to the first group of species, which also includes D. merguensis ( Bott, 1966) , D. thagatensis ( Rathbun, 1904) , and D. liui Shi, Chen & Sun, 2020 ; all from southern Myanmar.

Of the four species in the first group of species, the carapace of D. sunthorni is proportionately the lowest, with the dorsal surface flattest ( Fig. 3B, C ) (cf. Yeo et al., 1999: fig. 6E, F; Shi et al., 2020: fig. 2A, C). In addition, the frontal region of D. sunthorni has relatively numerous blunt granules and the striae on the anterolateral margins are very strong ( Fig. 3A, B ) (versus granules and striae in the other species are distinctly lower and smoother; Yeo et al., 1999: fig. 6E, F; Shi et al., 2020: fig. 2A, C); the subhepatic, suborbital and pterygostomial regions are densely covered with distinct striae and granules ( Fig. 3C ) (versus smooth to weakly granulated in the other species; e.g., Shi et al., 2020: fig. 2C); the epigastric cristae are strongly granulated with the postorbital cristae joining the anterolateral margin as a series of strong granules ( Fig. 3B ) (versus epigastric cristae are sharp but smooth and the postorbital crista joins the anterolateral margin smoothly as a sharp ridge; Yeo et al., 1999: fig. 6E, F; Shi et al., 2020: fig. 2A); the external orbital tooth is more acutely triangular ( Fig. 3B ) (versus tooth more obtuse and wider; Yeo et al., 1999: fig. 6E, F; Shi et al., 2020: fig. 2A); the ischium of the third maxilliped is proportionately shorter ( Fig. 3E ) (versus distinctly more elongate; e.g., Shi et al., 2020: fig. 3C); the G1 is proportionately more slender male telson has the lateral margins distinctly concave ( Fig. 4C, D ) (margins gently convex in D. liui ; Shi et al., 2020: fig. 2E); and the vulvae are proportionately much larger in size ( Fig. 5B ) (distinctly smaller in D. liui ; Shi et al., 2020: fig. 2H). The G1 terminal segment of D. sunthorni also resembles that of D. thagatensis but in the latter species, the terminal segment is not sharply bent at right angles, being more gradually angled and the dorsal fold is also low ( Yeo et al., 1999: fig. 3G, H).

In addition, while known species of Demanietta are generally aquatic (cf. Yeo et al., 1999), D. sunthorni appears to have more semiterrestrial habits.

with the basal part of the subterminal segment appearing less wide ( Fig. 6A, B ) (versus overall G1 stouter, with the basal part of the subterminal segment distinctly wider; Yeo et al., 1999: fig. 3A, B, E, F; Shi et al., 2020: fig. 3D, E); and the dorsal fold on the G1 terminal segment is higher and semicircular in shape ( Fig. 6D, E ) (versus dorsal fold is distinctly lower; Yeo et al., 1999: fig. 3C, D, G, H; Shi et al., 2020: fig. 3D, E).

In D. sunthorni , the epigastric and postorbital cristae are separated by a distinct space ( Fig. 3B ), and in this feature, agrees with D. thagatensis and D. liui (cf. Yeo et al., 1999: fig. 6F; Shi et al., 2020: fig. 2A); although in D. thagatensis , the epigastric cristae protrude more anteriorly toward the frontal margin than the other species ( Yeo et al., 1999: fig. 6F). The G1 structure of D. sunthorni ( Fig. 6D, E ) is most similar to that of D. liui in that the terminal segment is distinctly sinuous, bent at an angle of about 90° to the longitudinal axis with the tip slender, tapering and curned upwards. In D. liui , however, in addition to the earlier carapace differences listed between species, the distal part is more strongly upcurved and the dorsal flap is low ( Shi et al., 2020: fig. 3D, E). In addition, the median lobe of the posterior margin of the epistome is acutely triangular ( Fig. 3C, D ) (the median lobe is proportionately wider in D. liui ; Shi et al., 2020: fig. 2C, D); the tubercles of the male pleonal locking mechanism in D. sunthorni is positioned on the posterior third of sternite 5 ( Fig. 5A ) (the tubercles are submedian in position in D. liui ; Shi et al., 2020: fig. 2F); the Notes on habitat. Large specimens of D. sunthorni , new species, were found in deep burrows beneath large rocks about 20 m from the nearest stream ( Fig. 7B ). Smaller specimens inhabit banks near large streams which were in pristine tropical rain forest, less than 100 m amsl. The stream bed consisted of stones and rocks, the water flow being moderate ( Fig. 7A ). In the stream, small specimens of the palaemonid prawn Macrobrachium neglectum (De Man, 1905) (cf. Wowor & Ng, 2010) were collected as well as juveniles of the fighting fish Betta cf. pugnax ( Cantor, 1850) (Anabantidae) and Channa cf. gachua ( Hamilton-Buchanan, 1822) .

Distribution. Demanietta sunthorni is currently known only in the vicinity of a freshwater creek on Adang Island, Tarutao National Park.

Figures

Fig. 2. Colour in life. A, B, Demanietta sunthorni, new species, holotype male (36.6 × 27.7 mm) (ZRC 2022.0826), Thailand.

Fig. 3. Demanietta sunthorni, new species, holotype male (36.6 × 27.7 mm) (ZRC 2022.0826), Thailand. A, overall dorsal habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, antennae, antennules and epistome; E, left third maxilliped.

Fig. 4. Demanietta sunthorni, new species, holotype male (36.6 × 27.7 mm) (ZRC 2022.0826), Thailand. A, outer view of chelae; B, right fourth ambulatory leg; C, anterior thoracic sternum, telson and pleonal somite 6; D, pleon.

Fig. 5. Demanietta sunthorni, new species. A, holotype male (36.6 × 27.7 mm) (ZRC 2022.0826), Thailand; B, paratype female (38.5 × 29.4 mm) (PSUZC 20081020-01.01), Thailand. A, male sternopleonal cavity with right G1 and G2 in situ; B, female sternopleonal cavity and vulvae.

Fig. 6. Demanietta sunthorni, new species, holotype male (36.6 × 27.7 mm) (ZRC 2022.0826), Thailand. A, left G1 (ventral view); B, left G1 (dorsal view); C, distal part of left G1 (ventral view); D, distal part of left G1 (dorsal view); E, left G2. Scales: A, B, E = 1.0 mm; C, D = 0.5 mm.

Fig. 7. A, closest stream adjacent to locality of holotype, Adang Island, Langu District, off Satun Province, south Thailand; B, digging up the burrow of the holotype male.