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Macrobrachium prachuapense Saengphan & Panijpan, sp. nov. ( Figs. 2 – 4 ) Material examined. Holotype: male (carapace length (CL) 8.8 mm), 6 April 2018, Khao Chao subdistrict, Pran Buri district, Prachuap Khiri Khan Province (12°20.898′ N, 99°41.829′ E). Paratypes: 7 males (CL 5.9–9.4 mm) and 11 females (5.3–9.0 mm), same location and date as holotype. Others: 4 males (6.1–9.2 mm) and 5 females (5.5–7.8 mm), 7 April 2018, Huai Mae Phriang subdistrict, Kaeng Krachan district, Petchaburi Province (12°57.565′ N, 99°24.101′ E). The holotype (THNHM-Iv-18710) and some paratype specimens (THNHM-Iv-18711, THNHM-Iv- 18712, and THNHM-Iv-18713) of the described species were deposited at the Thailand Natural History Museum. Other specimens were kept at Suphanburi College of Agriculture and Technology, the workplace of the first author. Largest male: total length 42.0 mm, carapace length 9.4 mm (fig. 2) Largest ovigerous female: total length 39.0 mm, carapace length 9.0 mm. Description. (Fig. 3A) Rostrum: straight, dorsal margin convex, extending slightly beyond end of antennal peduncle, subequal to half of carapace length; upper part having 11–15 teeth (usually 11–12), 3–4 teeth behind post orbital margin; lower part having 1–4 teeth (usually 2). Carapace: smooth with fine spinules at antero-ventral surface; antennal spine well developed with pointed end and situated below orbital angle (suborbital angle); hepatic spine smaller than antennal spine and located slightly behind and lower than antennal spine; paired hepatic spines situated between upper first and third teeth of rostrum on carapace. Abdomen: fourth thoracic sternite without median process; sixth abdominal somite 1.40–1.53 times as long as fifth; first, second, and third abdominal sternites having transverse ridges with median teeth only on first and second; preanal region with rounded ridge. Telson: upper telson (fig. 3B) smooth and 1.52–2.20 times length of sixth segment with 2 dorsal paired spines; tail tapering toward rear with pointed end (median spine), each side flanked by 2 spines, outer lateral spine and inner intermediate spine; several pairs of plumose setae found between 2 flanking spines; lateral spines similar in size to dorsal spines; well-developed intermediate spines 2–3 times length of median spine. Eyes: well developed with cornea diameter as long as stalk. Basal segment of antennal peduncle: broad, stylocerite distinctly pointed, reaching to about one-third of basal segment; anterolateral tooth reaching about middle of second segment; second segment as long as third. Scaphocerite (fig. 3C): length 2.78 times width, outer lateral side straight. Epistome (fig. 3D): trilobed by deep depression, but occasionally anteromedian lobe indistinct. Mandibular palp (fig. 3E): slender with three segments, incisor process robust. Maxillular palp (fig. 3F): bilobed, upper lobe stout with apical and subapical setae, lower lobe stout with distal blunt knob bearing short sinuous apical seta. Maxillary palp (fig. 3G): simple without distal setae, basal endite deeply bilobed, scaphognathite normal. First maxilliped (fig. 3H): palp with apical setae, basal and coxal endites distinct, flagellum of exopod with numerous distal plumose setae, epipod bilobed. Second maxilliped (fig. 3I): with normal endopod, flagellum with numerous distal setae, epipod simple. Third maxilliped (fig. 3J): with robust endopod, exopod with numerous distal plumose setae, reaching up to distal margin of ischiomerus. First pereiopod (fig. 3K): slender, end of carpus reaching end of scaphocerite, equal in length, similar in form; palm as long as finger, carpus 1.80 times as long as chela, merus shorter than carpus. Second pereiopod (fig. 4): distinctly unequal in length but similar in shape; major second pereiopod reaching beyond scaphocerite by end of merus, as long as or prolonging to noticeably longer than total length; palm, finger, and on proximal ½–4/5 on dorsal and ventral parts of carpus covered with long velvet setae; merus not inflated, 4.25 times as long as height, subequal in length to palm, covered with numerous spinules over its length and sparsely with long velvet setae on certain spots; carpus elongated and subcylindrical, 2.75 times as long as height, with numerous spinules over its length; palm comparatively slender, subequal or shorter than fingers, 3.2 times as long as width, on proximal 1/5 of both lateral sides covered with spinules; fingers equal or longer than palm, 15–28 teeth on cutting edges, curved inwards, tips crossing and small gaping when closed. Minor second pereiopod: short, about 0.74–0.9 times of total length; fingers 1.3–2.0 times as long as palm, with numerous teeth (13–15 teeth) on proximal ¾–4/5 of both cutting edges; merus 1.5–1.6 times as long as carpus; palm subequal to carpus, 2.7 times as long as wide, with setae as on major second pereiopod. Last three pereiopods: slender, similar in form; propodus, carpus, and merus covered with spinules and setae. Third pereiopod (fig. 3L): reaching or nearly so to end of scaphocerite; propodus 2.72–3.08 times as long as dactylus with 7 movable spines on postero-lateral margin. Fifth pereiopod: somewhat slenderer than third, reaching or nearly so to distal margin of scaphocerite. First pleopod: endopod not reaching distal half of exopod, inner margin concave, outer margin slightly convex. Appendix musculina of male: longer and stouter than appendix interna with numerous stiff setae. Uropodal diaeresis: with inner movable spine (fig. 3M) longer than outer angle. Ovigerous females: with eyed eggs 1.10×1.45 – 1.28× 1.75 mm in diameter, 25–45 per ovigerous female. Etymology. The specific name “ prachuapense ” refers to the collection site of the holotype, Prachuap Khiri Khan Province, which is commonly called Prachuap. Molecular phylogeny. DNA sequences: COI 667 base pairs (bp), consensus alignment 678 bp; 18S 1446 bp, consensus alignment 1458 bp. The COI alignment contained 293 variable sites, 245 of which were informative. The 18S alignment contained 127 variable sites, 62 of which were informative. However, only five of these 62 informative sites were useful for phylogenetic analysis within the Macrobrachium pilimanus species group. Genetic distances: Table 3 shows the pairwise p -distances among the COI sequences of Macrobrachium prachuapense sp. nov. and M. naiyanetri. It clearly indicates that M. prachuapense sp. nov. is significantly different from M. naiyanetri from the southern part of Thailand from where the holotype was collected. Table 4 shows the average interspecific p -distances among the COI sequences of the clades containing multiple closely-related sequences (pairwise p -distances p -distance among the COI sequences within each clade. The clades in Tables 4 and 5 are based on the phylogenetic relationship in fig. 5. Phylogenetic relationship (fig. 5): Based on the combined (COI and 18S) sequences, Macrobrachium prachuapense sp. nov. is novel and different from the other closely related species. The novel prawn and M. naiyanetri with COI accession numbers MT235951 and MT235960 form monophyletic clade (clade A), posterior probability 1; clade A and other M. naiyanetri (clade B) form monophyletic clade (clade P), posterior probability 0.94; clade P and M. forcipatum (clade C) form monophyletic clade (clade Q), posterior probability 1; clade Q and M. palmopilosum Siriwut et al., 2020 (clade D) form monophyletic clade (clade R), posterior probability 0.76; clade R and M. malayanum with COI accession numbers MT235965 –6 (clade E) form monophyletic clade (clade S), posterior probability 0.59; M. puberimanus Siriwut et al., 2020 and M. sp. (cf. dienbienphuense) form monophyletic clade (clade H), posterior probability 1; clade H and M. dienbienphuense (clade G) form monophyletic clade (clade T), posterior probability 1; clade T, M. hirsutimanus (Tiwari, 1952) (clade I), and M. eriocheirum (clade J) form monophyletic clade (clade U), posterior probability 1; clades S and U and M. malayanum with COI accession numbers MT235959 and MT235964 (clade F) form monophyletic clade (clade V), posterior probability 1; clade V and M. sirindhorn Naiyanetr, 2001 (clade K) form monophyletic clade (clade W), posterior probability 1; M. niphanae Shokita & Takeda, 1989 (clade L) and M. chainatense Saengphan et al., 2019 (clade M) form monophyletic clade (clade X), posterior probability 1; clades W and X form monophyletic clade (clade Y), posterior probability 1; clade Y and M. saengphani Saengphan et al., 2020 form monophyletic clade (clade Z), posterior probability 0.56; M. sintangense (de Man, 1898) (clade N) and M. suphanense Saengphan et al., 2018 (clade O) form monophyletic clade (clade AA), posterior probability 1; M. lanchesteri (de Man, 1911) and M. rosenbergii (de Man, 1879) form monophyletic clade (clade AB), posterior probability 1; clades AA and AB form monophyletic clade (clade AC), posterior probability 0.57; clades Z and AC are sisters, posterior probability 1., Published as part of Saengphan, Nukul, Panijpan, Bhinyo, Senapin, Saengchan, Laosinchai, Parames, Suksomnit, Auaree & Phiwsaiya, Kornsunee, 2021, Morphology and molecular phylogeny of Macrobrachium prachuapense sp. nov. (Decapoda: Palaemonidae) from Southern Thailand, pp. 428-442 in Zootaxa 4966 (4) on pages 432-437, DOI: 10.11646/zootaxa.4966.4.2, http://zenodo.org/record/4738718, {"references":["Siriwut, W., Jeratthitikul, E., Panha, S., Chanabun, R. & Sutcharit, C. (2020) Molecular phylogeny and species delimitation of the freshwater prawn Macrobrachium pilimanus species group, with descriptions of three new species from Thailand. PeerJ, 8, e 10137. https: // doi. org / 10.7717 / peerj. 10137","Tiwari, K. K. (1952) Diagnosis of new species and subspecies of the genus Palaemon Fabricius (Crustacea: Decapoda). Annals and Magazine of Natural History, 5, 27 - 32. https: // doi. org / 10.1080 / 00222935208654260","Naiyanetr, P. (2001) Macrobrachium sirindhorn n. sp., a new freshwater prawn from northern Thailand (Decapoda, Caridea, Palaemonidae). Crustaceana, 74, 609 - 616. https: // doi. org / 10.1163 / 156854001750377885","Shokita, S. & Takeda, M. (1989) A new freshwater prawn of the genus Macrobrachium (Decapoda: Caridea: Palaemonidae) from Thailand. Bulletin of the National Science Museum, Tokyo, 15, 147 - 154.","Saengphan, N., Panijpan, B., Senapin, S., Laosinchai, P., Ruenwongsa, P., Suksomnit, A. & Phiwsaiya, K. (2019) Macrobrachium chainatense sp. nov. (Decapoda: Palaemonidae): a freshwater prawn from Thailand base on morphology and molecular phylogeny. Zootaxa, 4664, 274 - 284. https: // doi. org / 10.11646 / zootaxa. 4664.2.9","Saengphan, N., Panijpan, B., Senapin, S., Laosinchai, P., Suksomnit, A. & Phiwsaiya, K. (2020) Morphology and molecular phylogeny of Macrobrachium saengphani sp. nov. (Decapoda: Palaemonidae): from Northern Thailand. Zootaxa, 4868 (4), 531 - 542. https: // doi. org / 10.11646 / zootaxa. 4868.4.4","de Man, J. G. (1898) Zoological results of the Dutch scientific expedition to Central Borneo. The crustaceans. Part I. Macroura. Notes from the Leyden Museum, 20, 137 - 161.","Saengphan, N., Panijpan, B., Senapin, S., Laosinchai, P., Ruenwongsa, P., Suksomnit, A. & Phiwsaiya, K. (2018) Morphology and molecular phylogeny of Macrobrachium suphanense sp. nov. (Decapoda: Palaemonidae) from Thailand. Zootaxa, 4482 (1), 151 - 163. https: // doi. org / 10.11646 / zootaxa. 4482.1.7","de Man, J. G. (1911) On the West-African species of the subgenus Eupalaemon Ortm. Notes from the Leyden Museum, 33, 261 - 264.","de Man, J. G. (1879) On some species of the genus Palaemon Fabr. with descriptions of two new forms. Notes from the Leyden Museum, 41, 165 - 184."]}

Macrobrachium saengphani, sp. nov. (Figs. 2���7) Material examined. Holotype: male (CL 6.5 mm), 16 January 2017, Lao River, Tha Sai subdistrict, Mueang district, Chiang Rai Province (19��52.098��� N, 99��51.478��� E). Paratypes: 4 males (CL 5.8���6.5 mm), same location and date as holotype. Others: 3 males (6.2���6.5 mm) and 4 females (6.8���9.4 mm), 15 January 2017, Ing River, Si Don Chai subdistrict, Chiang Khong district, Chiang Rai Province (20��12.193��� N, 100��26.843��� E); 3 males (6.0��� 6.6 mm) and 6 females (9.0��� 11.5 mm), 15 January 2017, Kok River, Ban Saeo subdistrict, Chiang Saen district, Chiang Rai Province (20��12.854��� N, 100��05.282��� E). Largest male: total length 31.0 mm, carapace length 6.6 mm, smaller than fully grown female (fig. 2). Largest ovigerous female: total length 49.0 mm, carapace length 11.5 mm. Description. (Fig. 3A) Rostrum: straight, slender, upturned distally, extending beyond or slightly shorter than end of scaphocerite, length subequal to carapace; upper part having 6���8 teeth, 1���2 (usually 2) teeth behind postorbital margin; lower part having 4���5 (usually 4) teeth; distance between first anterior tooth and second one being longer than varying distances between succeeding teeth. Antennal spine: well developed with pointed end and situated below orbital angle (suborbital angle); hepatic spine of size similar to that of antennal spine and located slightly behind and lower than antennal spine; paired hepatic spines on carapace situated between upper first and second rostral teeth. Carapace: smooth; thoracic sternite of fourth segment with small median process; sixth abdominal somite 1.27���1.55 times as long as fifth; upper telson (fig. 3B) smooth and 1.47���1.61 times the length of sixth segment with 2 dorsal paired spines; tail tapering with pointed end (median spine) and bulging slightly at mid-section, each side flanked by 2 spines, outer lateral spine and inner intermediate spine; several pairs of plumose setae found between 2 flanking spines; lateral spines similar in size to dorsal spines; well-developed intermediate spines 2���3 times the length of median spine; first, second and third abdominal sternites having transverse ridges with median teeth; third abdominal having smaller median tooth; preanal region unarmed. Eyes: well developed, cornea diameter as long as stalk. Basal segment of antennular peduncle: broad, stylocerite distinctly pointed, reaching about one-third of basal segment; anterolateral tooth reaching about middle of second segment; second segment as long as third. Scaphocerite (fig. 3C): length 3.15 times the width, outer lateral side straight. Epistome (fig. 3D): bilobed by deep depression. Mandibular palp (fig. 3E): slender with three segments, incisor process robust. Maxillular palp (fig. 3F): bilobed, upper lobe slender without apical and subapical setae, lower lobe stout with distal blunt knob bearing short sinuous apical seta. Maxillary palp (fig. 3G): simple without distal setae, basal endite deeply bilobed, scaphognathite normal. First maxilliped (fig. 3H): palp without setae, basal and coxal endites distinct, flagellum of exopod with numerous distal plumose setae, epipod bilobed. Second maxilliped (fig. 3I): with normal endopod, flagellum with numerous distal setae, epipod simple. Third maxilliped (fig. 3J): with robust endopod, exopod with numerous distal plumose setae, reaching extremity of ischiomerus. First pereiopod (fig. 3K): slender, reaching nearly end of scaphocerite, equal in length, similar in form; palm as long as finger, carpus 2.27 times as long as chela, merus shorter than carpus. Second pereiopod (fig. 3L): smooth, carpus reaching slightly beyond scaphocerite, subequal to half of body length; equal in length, similar in form; palm, carpus, merus, ischium smooth; moving fingers bending upward, subequal to palm length, 2 small teeth at proximal half of cutting edge; fixed finger having acute end, proximal half of cutting edge armed with 2 or 3 small teeth, third tooth, if any, proximally adjacent to and smaller than second; both fingers curving inward, tips crossing without gap when fingers closed; both sides of cutting edge having stiff setae (fig. 3M), female with stiff setae concentrating proximally and delicate setae at tip, male with stiff setae throughout (fig. 4); carpus longer or as long as chela. Last three pereiopods: slender, similar in form; propodus, carpus, and merus covered with spinules and setae. Third pereiopod (fig. 3N): not reaching the end of scaphocerite, propodus 2.3���3.0 times as long as dactylus with 7 movable spines on postero-lateral margin. Fifth pereiopod: slightly slenderer than third, reaching distal margin of scaphocerite (end of dactylus and end of scaphocerite terminating at equidistance). First pleopod: endopod not reaching distal half of exopod, inner margin concave, outer margin slightly convex. Appendix musculina of male: longer, stouter than appendix interna with numerous stiff setae. Uropodial diaeresis: with inner movable spine (fig. 3O) shorter than outer angle. Ovigerous females: with eyed eggs 1.15��1.64 ��� 1.23�� 1.75 mm in diameter. Etymology. The species is named after the first author. The name, thus, is a noun in the genitive singular. Molecular phylogeny. DNA sequences: COI 668 base pairs (bp); majority of 18S 1446 bp; consensus alignment of 18S 1452 bp. Phylogenetic relationship (fig. 5): Macrobrachium suphanense and M. sintangense (de Man, 1898) form monophyletic clade (clade 1), posterior probability 1; M. chainatense and M. niphanae Shokita & Takeda, 1989 form monophyletic clade (clade 2), posterior probability 1; clade 2 and M. dienbienphuense Dang & Nguyen, 1972 form monophyletic clade (clade 3), posterior probability 1; clade 1 and clade 3 form monophyletic clade (clade 4), posterior probability 0.70; clade 4 and M. saengphani sp. nov. form monophyletic clade (clade 5), posterior probability 0.76; M. lanchesteri and M. rosenbergii form monophyletic clade (clade 6), posterior probability 1; clades 5 and 6 are sisters, posterior probability 1., Published as part of Saengphan, Nukul, Panijpan, Bhinyo, Senapin, Saengchan, Laosinchai, Parames, Suksomnit, Auaree & Phiwsaiya, Kornsunee, 2020, Morphology and molecular phylogeny of Macrobrachium saengphani sp. nov (Decapoda: Palaemonidae) from Northern Thailand, pp. 531-542 in Zootaxa 4868 (4) on pages 534-536, DOI: 10.11646/zootaxa.4868.4.4, http://zenodo.org/record/4443533, {"references":["Shokita, S. & Takeda, M. (1989) A new freshwater prawn of the genus Macrobrachium (Decapoda: Caridea: Palaemonidae) from Thailand. Bulletin of the National Science Museum, Tokyo, 15, 147 - 154."]}

Saengphan, Nukul, Panijpan, Bhinyo, Senapin, Saengchan, Laosinchai, Parames, Suksomnit, Auaree, Phiwsaiya, Kornsunee (2020): Morphology and molecular phylogeny of Macrobrachium saengphani sp. nov (Decapoda: Palaemonidae) from Northern Thailand. Zootaxa 4868 (4): 531-542, DOI: https://doi.org/10.11646/zootaxa.4868.4.4

Macrobrachium suphanense, sp. nov. Figs. (2–6) Material examined. Holotype: male (cl 8.5 mm), Nikhom Krasiao subdistrict, Dan Chang district, Suphan Buri Province (14°49′50.3″ N, 99°34′52.5″ E), 28 February 2013. Paratypes: 11 males (cl 2.5–7 mm), same location and date as holotype. Others: 15 males (cl 5–8 mm) and 8 females (cl 7–8.6 mm), Don Chedi subdistrict, Don Chedi district, Suphan Buri Province (14o37′37.7″ N, 100o0′43.2″ E), 21 March 2013; 15 males (cl 5–8 mm) and 8 females (cl 7–8.6 mm), Pho Muang Phan subdistrict, Samko district, Ang Thong Province (14o35′19.6″ N, 100o15′38.4″ E), 21 March 2013; 2 males (cl 9 and 11 mm), Chorakhe Sam Phan subdistrict, U Thong district, Suphan Buri Province (14o19′42.4″ N, 99o51′58.3″ E), 7 June 2016; 15 males (cl 5–8 mm) and 8 females (cl 7–8.6 mm), Hua Wiang subdistrict, Sena district, Ayutthaya Province (14o22′13.2″ N, 99o24′51.0″ E), 1 July 2012; 20 males (cl 3–6.5 mm) and 24 females (cl 4–8.2 mm), Srinagarindra dam, Si Sawat district, Kanchanaburi Province (14o35′50.1″ N, 99o6′33.0″ E), 13 December 2014. Largest male: total length of 42 mm, carapace length 10 mm. Ovigerous female. Largest: total length of 42 mm, carapace length 12.2 mm; smallest: total length of 27 mm, carapace 7.2 mm. Description. Fully grown male (fig. 2 A): Rostrum: straight, elevating over eye sockets bending downward gradually to straight tip, extending beyond or as long as the antennular peduncle (but not reaching the end of scaphocerite), length about three quarters of carapace; upper part having 9–12 teeth, 2 teeth behind the eye socket (post orbital margin); lower part of rostrum having 3–4 teeth; distance between the first posterior tooth and the second tooth being longer than distances between the adjacent teeth in the middle (fig. 3). Antennal spine: well developed with pointed end and situated below orbital angle (suborbital angle); hepatic spine of size similar to that of antennal spine and located slightly behind and lower than antennal spine; paired hepatic spines parallel to antennal spines situated between upper first and second teeth of rostrum on carapace. Carapace: smooth with tiny protruding "spines" sparsely scattered but more densely populated at anterior and ventral region; thoracic sternite of fourth segment having conical median process; tiny spinules found on shell of abdominal pleurae; spinules sparsely scattered near lower edges of segments no. 3, 4, and 5; sternite no. 6 shell 1.8 times as long as that of sternite no. 5; upper telson (fig. 4) segment smooth and 1.44 times longer than segment no. 6 with 4 dorsal unpaired spines (paired ones in paratype) at the tail end; tail tapering toward the rear with a pointed end (median spine), each side flanked by 2 spines, outer lateral spine and the inner intermediate spine; several pairs of plumose setae found between the two flanking spines; lateral spines having similar size to dorsal spines; welldeveloped intermediate spines 3 times the length of median spine; abdominal sternites no. 1–3 having transverse ridges with median teeth on sternites no. 1 and 2; median tooth on sternite no. 2 larger than that on no. 1; abdominal sternite no. 3 having no median tooth; preanal region unarmed. Eyes: well developed with cornea diameter shorter than stalk. Basal segment of antennular peduncle: broad, stylocerite distinctly pointed, reaching to about one-third of basal segment; anterolateral tooth reaching to about middle of second segment; second segment as long as third segment. Scaphocerite (fig. 2B): longer by 3.2 times than the width, outer lateral side straight. Mandibular palp (fig. 2C): slender with three segments, incisor process robust. Maxillular palp (fig. 2H): bilobed, upper lobe slender bearing 1–3 apical setae and 3–4 subapical ones at both lateral faces, lower lobe stout with distal blunt knob bearing a long sinuous apical seta. Maxillar palp (fig. 2D): palp with numerous setae proximally, basal endite deeply bilobed, scaphognathite normal. First maxilliped (fig. 2E): with setose palp, basal and coxal endites distinct, flagellum of exopod with numerous plumose setae distally, epipod deeply bilobed. Second maxilliped (fig. 2F): with normal endopod, flagellum with numerous setae distally epipod simple, with well-developed podobranch. Third maxilliped (fig. 2G): with robust endopod, exopod with numerous plumose setae distally, reaching to distal margin of ischiomerus. First pereiopod: slender, reaching beyond scaphocerite by entire distal margin of carpus, equal in length, similar in form. Palm as long as finger, carpus 1.79 times as long as chela, merus shorter than carpus; both fingers ending in very small apical claw concealed by apical curved cutting edge. Male second pereiopod equal in length, similar in form. Second pereiopod: reaching beyond scaphocerite by one-third of merus length, longer than total length; palm, carpus, menus, ischium covered with spinules with lower ones smaller than upper ones and bending towards legs; upper spinules obtuse. Movable finger curving toward the fixed finger tapering to a tip, 0.9 palm length, coated with long velvety hairs on proximal two-thirds (fig. 5), distal with some tiny or inconspicuous crescent-shaped tubercles present on inner side of the cutting edges; 2 conical strong teeth in proximal one-sixth of cutting edge of movable finger (fig. 6). Fixed finger ending in acute, downward curving apical claw, coated with velvety hairs on proximal two-thirds; proximal one-sixth of cutting edge armed with a strong conical tooth preceded by a low obtuse bifid triangular tooth. Both fingers curving inwards, tips crossing and not gaping when fingers closed; palm cylindrical, length 2.9 times of width; carpus distinctly shorter than chela (14:19), longer than palm. Last three pereiopods: slender, similar in form; propodus, carpus, merus, covered with spinules and setae. Third pereiopod: reaching beyond scaphocerite by one-fourth to two-fifths of propodus (part of propodus extending beyond the end of scaphocerite equal to one quarter to two-fifths of propodus length), propodus 3.33 times as long as dactylus with about 8 (paratype 12) movable spines on postero-lateral margin. Fifth pereiopod: somewhat slenderer than the third, propodus ending beyond distal margin of scaphocerite (end of propodus and end of scaphocerite terminating in equidistance). Endopod of male: first pleopod not reaching distal half of exopod, inner margin concave, outer margin slightly convex. Appendix musculina of male: longer, stouter than appendix internal with numerous stiff setae. Uropodial diaeresis (fig. 4): with inner movable spine longer than outer angle (in paratype as long as outer angle). Ovigerous females: with eggs 1.0 × 1.3 mm to 1.1 × 1.5 mm in diameter (n=25). Habitat. Inhabiting small stagnant water bodies, e.g. irrigation channels where the others not found. Etymology. Location of first collections. DNA sequence alignment and phylogenetic relationships. The COI sequence lengths were 668 base pairs (bp). The alignment of 18S sequences yielded a consensus whose length was 1453 bp while the majority of the 18S sequences were 1446 bp. Thus indels did not present much of a problem in the alignment. The combined dataset was 2121 bp. For Bayesian inference, GTR+G was selected as the nucleotide substitution model for all the partitions. The phylogenetic trees reconstructed from the three datasets are shown in fig. 7. It can be seen that the partial COI and 18S rRNA genes were capable of grouping closely related species in this study together, as shown by high posterior probabilities supporting the clades toward the tips of the trees. For COI, the genetic differences within each clade, as shown by the length from the vertex of an isosceles triangle to its base (the height of the isosceles triangle) or the branch lengths from the node to the tips, tended to be small compared to the differences between clades, indicated by the branch lengths from the ancestral nodes to those taxa. M. suphanense was most closely related to M. sintangense (de Man, 1898) and the two species formed a monophyletic clade with posterior probability of at least 0.98. This clade, in turn, form a monophyletic clade with M. nipponense (de Haan) with posterior probability of 1. The clade containing the three species will be called clade 1. M. niphanae Shokita & Takeda, 1989 and M. dienbienphuense Dang & Nguyen, 1972 also formed a monophyletic clade with posterior probability of at least 0.96. M. lanchesteri (de Man, 1911) and M. rosenbergii (de Man, 1879), despite their differences in size, were closely related, with supporting posterior probability of 1. Unfortunately, COI and 18S genes yielded different relationship among clade 1 and the other two clades (figs. 7 A and 7B). Remarks. Fully grown males of M. suphanense (wild and bred) had features similar to fully grown males (wild and bred) of M. sintangense, M. dolatum Cai et al., 2004, M. hungi Xuan, 2012 and M. equidens (Dana, 1852), yet it was different from M. sintangense in that: 1) the form of the rostrum: narrower midway with straight end whereas that of M. sintangense broad midway with end curving upward; 2) the number of teeth on rostrum: 9– 10 (including teeth behind orbital margin 2) / 3 (ventral) versus 9–13 (including teeth behind orbital margin 2–4) / 3–5 (ventral) in M. sintangense (collected); 3) second pereiopods appeared less robust than those in M. sintangense; 4) smaller body size: the largest male was 42 mm versus 71 mm in M. sintangense (collected) (fig. 8); 5) found mainly in small still water bodies vs running water for M. sintangense; 6) fecundity of ovigerous female was lower: the number of eggs varied from 30–111 versus 159–272 in M. sintangense. The new species differed from M. dolatum in that: 1) cutting edge of distal part of the fixed finger not razorlike versus M. dolatum with razor-like edge; 2) spine at the uropodal diaeresis equal to or longer than the outer angle versus shorter in M. dolatum. The new species can be differentiated from M. hungi found in Cambodia by: 1) body size smaller: the largest male 42 mm versus 98.5 mm in M. hungi; 2) rostrum shorter: not reaching scaphocerite versus reaching beyond the distal margin of scaphocerite in M. hungi; 3) the number of teeth on rostrum fewer than in M. hungi: 9–10 / 3, versus 13–15 / 5–7 in M. hungi. M. equidens preferring brackish water versus freshwater for M. suphanense. In each population fully grown dominant males are few (from one to a few). In our hands, the wild caught fully grown males and the ones reared in the laboratory were virtually in the same size range regardless of whether only one-species population growing up by themselves or growing up with another species. Molecular phylogeny. We have reconstructed phylogenetic trees (based on COI, 18S rRNA and combined sequence alignments) having M. suphanense in its relationship to extant, mostly local Macrobrachium species. It is clear that M. suphanense is a new species with the posterior probability supporting the clade in all the trees being 1 indicating clear genetic differences from its sister clade, M. sintangense. It is also clear that this new species is not a hybrid of extant species because its phylogenetic relationships to other closely related Macrobrachium species (M. sintangense and M. nipponense) from both the nuclear 18S and the mitochondrial COI genes agree (figs. 7 A and 7B). In fact, there are 2 specimens (M. sp. from Beungkan and Chainat) whose locations on the phylogenetic trees reconstructed from single genes differ, indicating that they are potential hybrids. For the specimen from Chainat, its COI gene indicates that it is an M. suphanense while its 18S gene falls within the clade M. niphanae. The other specimen’s COI gene forms a monophyletic clade with M. niphanae while its 18S gene is related to those of M. lanchesteri and M. rosenbergii. As regards species identification by DNA sequences of other known species and their relative positions on the phylogenetic tree, our molecular phylogenetic results of those valid species based on the COI and combined datasets are consistent with those already published for M. sintangense, M. nipponense, M. niphanae, M. lanchesteri and M. rosenbergii (Wowor et al., 2009) based on 18S+28S rRNAs (nuclear). Another noticeable feature common between our and Wowor et al.’s results is that the resolution of the phylogeny tends to be poorer toward the root of the Macrobrachium clade as shown by low posterior probabilities supporting them. That the new species, M. suphanense, is not a hybrid of recent extant species is supported by over 10 generations of breeding resulting in only one type of prawns with identical and distinctive developmental and fully grown features (our observation). As indicated above, we are capable of detecting hybrids by DNA analysis, and are certain that M. suphanense is not a hybrid, but a pure species.