Macrobrachium rostrolevatus Chaowvieng & Siriwut, 2024

Chaowvieng, Apisara, Sutcharit, Chirasak, Chanabun, Ratmanee, Srisonchai, Ruttapon, Jeratthitikul, Ekgachai & Siriwut, Warut, 2024, Molecular phylogeny and taxonomic position of Macrobrachium lanchesteri (De Man, 1911), with descriptions of two new species from Thailand (Decapoda, Caridea, Palaemonidae), ZooKeys 1190, pp. 163-193 : 163

Macrobrachium rostrolevatus Chaowvieng & Siriwut sp. nov.

Figs 3C, D , 6

Material examined.

Holotype: Bueng Kan • Ovigerous ♀ from Bueng Khong Long; 17°59'59.1"N, 104°01'06.9"E; CUMZ MP00323. Paratypes: 10 ♀♀, 13 ovigerous, 7 ♂♂ from the same locality of holotype; MUMNH MP00324 .

Additional material.

Nong Khai • 3 ♀♀, 2 ♂♂, Nam Suai , Song Hong, Mueang Nong Khai; 17°45'01.1"N, 102°51'00.5"E; MUMNH MP00325. Udon Thani • 10 ♀♀, 4 ovigerous, 2 ♂♂, Si Charoen , Ban That, Phen; 17°42'47.7"N, 102°50'57.4"E; MUMNH MP00326 . • 3 ♀♀, 1 ovigerous, Nam Khong , Thap Kung, Nong Saeng; 17°10'01.5"N, 102°46'03.2"E; MUMNH MP00327. Loei • 1 ♀, Tha Yang , Phu Kradueng; 16°53'38.3"N, 101°52'53.1"E; MUMNH MP00354. Nakhon Phanom • 2 ♀♀, 3 ♂♂, Klong Kam , Na Khu, Na Kae; 16°57'42.3"N, 104°31'33.2"E; MUMNH MP00328 . • 1 ♀, Huai Saab , Sam Phong, Si Songkhram; 17°43'59.2"N, 104°09'19.9"E; MUMNH MP00329. Sakon Nakhon • 1 ♀, Nam Chan , Akat, Akat Amnuai; 17°35'46.1"N, 104°00'21.6"E; MUMNH MP00330 . • 1 ♂, Klong Lak , Chiang Khruea, Mueang Sakon Nakhon; 17°15'33.7"N, 104°07'00.1"E; MUMNH MP00331 . • 1 ♂, Klong Un , Khok Phu, Phu Phan; 17°00'22.1"N, 103°54'50.5"E; MUMNH MP00332 . • 1 ♀, Tha Rae , Mueang Sakon Nakhon; 17°15'08.5"N, 104°09'32.0"E; MUMNH MP00352. Kalasin • 1 ♀, 2 ♂♂, Huai Sathot , Kham Bong, Huai Phueng; 16°41'32.6"N, 103°51'20.1"E; MUMNH MP00333 . • 18 ♀♀, 2 ovigerous, 10 ♂♂, Bueng Aram , Khlong Kham, Yang Talat; 16°24'21.8"N, 103°20'26.4"E; MUMNH MP00334. Khon Kaen • 10 ♀♀, 2 ♂♂, Kong Kaeo Reservoir , Si Bun Rueang, Chonnabot; 16°05'47.2"N, 102°37'05.4"E; MUMNH MP00335. Maha Sarakham • 3 ♂♂, Ban Tha Tum , Mueang Maha Sarakham; 16°10'55.8"N, 103°27'10.6"E; MUMNH MP00336. Yasothon • 8 ♀♀, 11 ♂♂, Se Bai , Sawat, Loeng Nok Tha; 16°10'13.5"N, 104°32'21.1"E; MUMNH MP00337 . • 11 ♀♀, 7 ovigerous, 12 ♂♂, Klong Wai , Fa Yat, Maha Chana Chai; 15°30'59.5"N, 104°15'12.3"E; MUMNH MP00338. Si Sa Ket • 13 ♀♀, 16 ovigerous, 2 ♂♂, Bueng Bun Local Market , Bueng Bun; 15°19'18.6"N, 104°03'01.2"E; MUMNH MP00339 . • 2 ♀♀, Huai Khayung , Thung Yai, Kantharalak; 14°34'42.1"N, 104°38'48.1"E; MUMNH MP00340. • 1 ovigerous, Suk San, Phran, Khun Han; 14°35'27.7"N, 104°29'29.3"E; MUMNH MP00353. Surin • 3 ♀♀, Klong Thap Than , Yang Sawang, Rattanaburi; 15°16'55.4"N, 103°58'38.1"E; MUMNH MP00341 . • 28 ♀♀, 9 ♂♂, Mun River , Tha Tum; 15°19'53.3"N, 103°38'34.9"E; MUMNH MP00342 . • 12 ♀♀, 13 ♂♂, Mun River , Krapho, Tha Tum; 15°17'38.5"N, 103°30'42.4"E; MUMNH MP00343 . • 3 ♀♀, Ban Kut Chum Saeng , Yawuek, Chumphon Buri; 15°18'57.6"N, 103°15'24.2"E; MUMNH MP00344. Buri Ram • 2 ovigerous , 1 ♂, Lam Chi , Non Charoen, Ban Kruat; 14°26'43.9"N, 103°12'55.8"E; MUMNH MP00345. Nakhon Ratchasima • 1 ♀, 7 ♂♂, Sathaet , Krabueang Nok, Mueang Yang; 15°27'35.2"N, 102°59'46.6"E; MUMNH MP00346 . • 4 ♀♀, 3 ♂♂, Sema , Sung Noen; 14°55'11.0"N, 101°47'53.5"E; MUMNH MP00347 . • 3 ♀♀, 2 ♂♂, Sawai Riang , Than Prasat, Non Sung; 15°16'13.3"N, 102°22'37.0"E; MUMNH MP00348 . • 1 ♂, Lam Takhong , Mu Si, Pak Chong; 14°33'00.7"N, 101°27'34.1"E; MUMNH MP00349 .

Diagnosis.

Rostrum long and thin, proximal half straight and uplifted distal half. Rostrum length reaching beyond end of antennular peduncle and prominently exceeding scaphocerite. Rostral formula: 6-11/4-9 teeth including 2-4 teeth distally with large gap from rest. Apical teeth usually present with trifid. Carapace smooth. Epistome bilobed. First pereiopods reaching end scaphocerite. Second pereiopods thin and long, similar in form and length, exceeding end of scaphocerite. Fingers covered with scattered setae with translucent razor edge present anteriorly between fingers and one tooth on proximal quarter of cutting edges. Palm 1.25 × longer than fingers. Carpus cylindrical shape and articulation margin expanded. Carpus 1.5-2 × longer than chela. Merus subcylindrical. Carpus 1.5 × longer than merus. Third pereiopods thin and long, slightly exceeding scaphocerite. Dactylus curved distally with short setae. Propodus 2 × longer than dactylus. Propodus with 3-6 pairs of spines distributed along its length and fine setae at its articulation. Propodus 2 × longer than carpus. Sixth to eighth thoracic sternites smooth. First and second pleonal sternites with small median process. Third and fourth pleonal sternites smooth. Fifth pleonal sternite with triangular ridge. Uropodal diaeresis with inner movable spine slightly longer than outer angle.

Composite description

(holotype in parenthesis). Rostrum (Fig. 6B ). Tapered and long, proximal half of rostrum straight and uplifted distally. Rostrum length exceeding end of antennular peduncle and distinctly exceeding scaphocerite (rl 10.34 mm). Dorsal margin with 6-11 (9) teeth including 2-4 (4) teeth distally separated from rest. Apical teeth usually present with trifid. Postorbital margin with 1 or 2 (1) teeth reaching one-third of carapace length. First dorsal tooth positioned slightly behind hepatic spine. Ventral margin with 4-9 (7) teeth, starting from middle to distal margin. Short setae present between rostral teeth.

Cephalon (Fig. 6B ). Eye well developed; ocular beak without laterally expanded tip. Cornea longer and broader than stalk. Postantennular carapace margin rounded. Cornea osculum longer than stalk. Antennular peduncle longer than wide, with fine setae. Basal segment short, second segment being shorter than third segment. Stylocerite projection sharp, reaching beyond basal segment. Antennal spine sharp, situated below orbital margin. Hepatic spine slightly larger than antennal spine, positioned posteriorly and lower than antennal spine. Scaphocerite with straight margin, distolateral tooth sharp and not reaching end of lamella. Epistome bilobed (Fig. 6D ). Branchiostegal suture starting from carapace margin to behind hepatic spine. Carapace surface smooth (cl 7.14 mm).

First pereiopods. Long and slender, reaching end of scaphocerite. Fingers as long as palm, tips with fine setae. Series of setae present at anterior inner part of palm. Carpus slightly longer than merus. Distal articulation of carpus with series of fine setae. Ischium shorter than merus. Scattered setae present on all segments.

Second pereiopods (Fig. 6E ). Long and slender, similar in form and distinctly exceeding the scaphocerite. Fingers subcylindrical covered with scattered setae. Palm 1.2-1.7 × longer than fingers (Fin 1.47: Pal 1.84 mm). Fingers with translucent razor edge present anteriorly and one tooth on cutting edges. Tip of fingers crossed and covered by fine setae (Fig. 6F ). Carpus cylindrical shape and articulation margin expanded. Carpus 1.5-2.0 × longer than chela (Che 3.31: Car 6.19 mm). Merus subcylindrical. Carpus 1.3-1.6 × longer than merus (Mer 3.99: Car 6.19 mm). Ischium as long as merus. Scattered short setae present on all segments.

Third pereiopods (Fig. 6G ). Long and slender, slightly exceeding scaphocerite. Dactylus curved distally with short setae. Propodus 2 × longer than dactylus (Dac 1.19: Pro 3.94 mm). Propodus with 3-6 (4) pairs of spines along inferior-lateral margin and fine setae at distal articulation, 2 × longer than carpus (Car 1.83: Pro 3.94 mm). Ischium shorter than carpus. Scattered short setae present on all segments.

Fourth and fifth pereiopods. Long and slender, exceeding scaphocerite. Propodus of fourth pereiopods with 4-7 (5) pairs of spines distributed along its length, 2 × longer than dactylus. Propodus slightly shorter than merus. Ischium shorter than merus. Propodus with fine setae at distal articulation. Scattered short setae present on all segments. Propodus of fifth pereiopods with 4-10 pairs of spines (holotype damaged) distributed along its length and fine setae at distal articulation. Propodus 2.5 × longer than carpus. Propodus as long as merus. Scattered short setae present on all segments.

Thoracic sternum. Fourth and fifth thoracic sternites with moderately transverse plate. Sixth to eighth thoracic sternites usually smooth.

Pleon. Smooth. All pleonal sternites with transverse ridge. First and second pleonal sternites with or without median process. Third and fourth pleonal sternites smooth. Fifth sternite with triangular ridge. Preanal carina present, obtuse ridge developed without spine or setae. Ventral margin of pleural tergum with small setae.

Telson (Fig. 6H ). Tapered posteriorly, protruding point on middle margin with lateral spines and few fine setae. Inner spines longer than outer spines. Dorsal surface with two pair of small spines, similar in size.

Uropods (Fig. 6H ). Uropodal diaeresis with inner movable spine, as long as or slightly longer than outer angle. Exopods longer than endopods.

Etymology.

The specific epithet rostrolevatus is from the Latin compound words rostro, for rostrum, and levatus, referring to lifted.

Distribution.

This species is distributed in freshwater basins of Khorat Plateau, Northeast Thailand.

Remarks.

Macrobrachium rostrolevatus sp. nov. differs from M. lanchesteri s. str. based on the presence of single tooth on movable and fixed fingers of second pereiopods (vs 1 or 2 teeth on movable and fixed fingers in M. lanchesteri ), movable spine at uropodal diaeresis slightly longer than the outer angle (vs shorter than outer angle in M. lanchesteri ), and the presence of 3-6 pairs of spines on propodus of third pereiopods (vs 4-8 pairs of spines in M. lanchesteri ). This new species also differs from M. villosimanus sensu Tiwari (1949) and M. rosenbergii sensu De Man (1879) by having 6-11/4-9 rostral teeth (vs 12-14/7-10 rostral teeth in M. villosimanus ; 9-13/10-15 rostral teeth in M. rosenbergii ). The second pereiopods are smooth and covered with fine setae (vs spinules in entire cheliped, movable finger densely pubescent and fixed finger sparsely pubescent in M. villosimanus ; coarse velvet hairs on movable finger except its tip, and fixed finger covered with numerous short spines in M. rosenbergii ). Moreover, this new species differs from M. lamarrei sensu H. Milne Edwards (1837) by processes 6-11/4-9 rostral teeth (vs 6-11/5-9 rostral teeth in M. lamarrei ). The movable spine at uropodal diaeresis is slightly longer than outer angle (vs without movable spine in M. lamarrei ). Further description of M. lamarrei was provided by Cai and Ng (2002). In addition, M. rostrolevatus sp. nov. is present only in freshwater basins on the Khorat Plateau, and lives in various habitats such as lakes, ponds, and river whereas M. villosimanus , M. rosenbergii and M. lamarrei typically inhabit brackish water territory.

Macrobrachium rostrolevatus sp. nov. exhibits phenotypic plasticity in rostral shape. The population in a lentic habitat such as a pond, paddy field and lake have an upcurved on distal half of rostrum. On the other hand, some populations have slightly convex at basal and upturned distally with a smaller gap between distal and proximal teeth of rostrum (Fig. 6C ). The taxonomic discrimination based on rostrum form in genus Macrobrachium is cautioned due to controversial situation found in this study. Additionally, the uncertain identity found from Thai Macrobrachium specimens was also mentioned in previous records. For example, Naiyanetr (1998) reported M. palaemonoides Holthuis, 1950 [= Tenuipedium palaemonoides in Wowor and Ng (2010)] from Surin Province. Re-examination of the collection by Cai et al. (2004) placed those specimens back under a typical variation of M. lanchesteri and mentioned that T. palaemonoides s. str. was known only from the original type locality in the west coast of Sumatra. The unique characteristics of T. palaemonoides are shown to be distinct from Macrobrachium such as its long branchiostegal groove, the second pereiopod is as wide as first pereiopod and the fourth and fifth pereiopods are longer than the second pereiopod.

Figures

Figure 3. Living habit of specimens of three Macrobrachium species A, B M. lanchesteri from Bang Khiat, Singhanakhon, Songkhla, Thailand C, D M. rostrolevatus sp. nov. from Bueng Khong Long, Bueng Kan, Thailand E M. panhai sp. nov. from Sri Nakarin Dam, Tha Kradan, Si Sawat, Kanchanaburi, Thailand. Scale bars: 1 cm.

Figure 6. Morphological characteristics of Macrobrachium rostrolevatus sp. nov. (A, B, D-I ovigerous female holotype CUMZ MP 00323 C ovigerous female specimen MUMNH MP 00338.1) A lateral view B carapace C rostral variation D epistome E second pereiopod F teeth between fingers G third pereiopod H uropod and I movable spine at uropodal diaeresis. Scale bars: 1 mm.