Macrobrachium agwi, KLOTZ, WERNER, 2008

KLOTZ, WERNER, 2008, Macrobrachium agwi-a new species of freshwater prawn (Decapoda: Palaemonidae) from East Bengal, India, Zootaxa 1844 (1), pp. 47-54 : 49-52

publication ID	https://doi.org/ 10.11646/zootaxa.1844.1.4
persistent identifier	https://treatment.plazi.org/id/03CC87B5-BC18-4B1C-9584-FEADFC297548
treatment provided by	Felipe
scientific name	Macrobrachium agwi
status	sp. nov.

Treatment

Macrobrachium agwi View in CoL , new species

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Material examined: Holotype —male, cl 17.4 mm, tl 53.8 mm ( RMNH D 51995), India, West Bengal, Alipurduar Distr., Barobisha, approx. 800 km north of Calcutta , from commercial aquarium import.

Paratypes — 1 male, cl 15.0 mm, tl 40.8 mm ( RMNH D 51996), same data as holotype ; 4 females, cl 12.0– 14.5 mm, tl 42.2–48.0 mm ( RMNH D 51996), same data as holotype ; 1 ovigerous female, cl 15.4 mm, tl 49.4 mm ( RMNH D 51996), same data as holotype . 2 males, cl 13.5 and 15.2 mm, tl 43.5 and 46.0 mm ( OUMNH. ZC.2008-01-001) same data as holotype ; 2 females, cl 10.5 and 13.7 mm, tl 39.0 and 40.0 mm ( OUMNH. ZC.2008-01-002) same data as holotype ; 1 ovigerous female, cl 14.9 mm, tl 45 mm ( OUMNH. ZC.2008-01-003), same data as holotype .

Comparative material examined: Macrobrachium hendersoni (De Man, 1906) : (1 male, cl 17 mm, tl 57 mm; 1 male cl 15 mm, tl 50 mm; 1 ovigerous female cl 12 mm, tl 39 mm) ( RMNH D 7686) Upper Pegu River, Pegu Jomas, Burma, February 1911, Leg. C.G. Rogers .

Description: Rostrum ( Fig. 2A View FIGURE 2 ) short, 0.37–0.52 times cl, reaching to distal end of 3 rd segment of antennular peduncle; upper margin convex above eyes, tip directed straight forward; upper margin with 7–10 teeth of which three or four post-orbital; space between the 1 st and 2 nd teeth wider than between distal ones; ventral margin with two or three teeth. Rostrum formula 3–4(3) + 4–6(4) / 2–3(2). Setae present between the teeth of dorsal and ventral margins. Carapace ( Fig. 2A View FIGURE 2 ) scabrous, covered with fine spinulation on dorsal and branchiostegal margin, antennal spine sharp, situated below lower orbital angle, hepatic spine well developed, situated below and behind the level of the antennal spine. Inferior orbital margin ( Fig. 2A,B View FIGURE 2 ) moderately produced, postantennular margin rounded. Cornea well developed, globular. First segment of the antennular peduncle 2.1–3.2 times as long as second, latter 1.3–2.3 as long as third. Stylocerite long, slender, sharp.

Epistome ( Fig. 2C View FIGURE 2 ) bilobed with deep depression between lobes.

First cheliped ( Fig. 2G View FIGURE 2 ) slender, glabrous, with several stiff scattered setae on all segments, chela 4.5– 5.1times as long as wide, dactylus 0.9–1.0 times as long as palm, carpus slender, 6.6–7.9 times as long as wide, 1.3–1.4 times as long as chela, 1.0–1.2 times as long as merus.

Second chelipeds similar in shape, somewhat unequal in length. Major second cheliped ( Fig. 3A–C View FIGURE 3 ) robust, covered with many small spinules on all segments except fingers, more developed on inner margin of ischium and merus, reaching with carpus beyond scaphocerite, as long as body length in full developed males. Chela 6.1–8.8 times as long as wide in males, 5.4–5.7 times as long in females; 3.0–4.3 times as long as carpus in males, 2.4–3.1 times as long in females. Palm cylindrical, slightly compressed, 3.0–3.5 times as long as wide, 1.6–1.7 times as long as carpus in males, 2.6–3.0 times as long as wide, 1.2–1.7 times as long as carpus in females, covered with fine spinules, not covered with dense fur-like seate. Fingers slender, slightly gaping in adult males, neither covered with fur-like setae nor distinctly grooved in both males and females but with indistinct dints arranged in rows with scarce stetae in large ovigerous females. Dactylus 0.9–1.1 times as long as palm with 2 large teeth in proximal half. Distal one conical, proximal one double, distal half of cutting edge entire. Fixed finger with two large teeth situated proximal of teeth on movable finger. Distal one conical, proximal one triple. Carpus elongated conical, covered with fine spinules, 2.1–2.4 times as long as wide, 0.8– 0.9 times as long as merus in males, 2.1–2.8 times as long as wide, 0.8–1.0 times as long as merus in females. Merus elongated conical, coverd with fine spinules, 2.7–3.3 times as long as wide, spinules more developed on lower margin.

Minor second cheliped ( Fig. 3D View FIGURE 3 ) resembling major but somewhat shorter and with less developed teeth on fingers.

Third pereiopod ( Fig. 2H View FIGURE 2 ) slender, without apressed scales. Dactylus ( Fig. 2I View FIGURE 2 ) simple, 0.38–0.53 times as long as propodus. Propodus 5.7–7.5 times as long as wide.

Sternum of 4 th thoratic segment ( Fig. 2D View FIGURE 2 ) without median process; with broad posterior submedian plate. Sternum of 8 th thoratic segment as pictured in Fig. 2E View FIGURE 2 . First three abdominal sternites ( Fig. 2F View FIGURE 2 ) with mediumsized ventrad directed median processes in similar form and size. Inter- uropodal sclerite without discernible preanal carina. Distal margin of telson ( Fig. 2J View FIGURE 2 ) convex, ending in a teeth-like triangular tip, with two pairs of movable spines; inner pair not extending beyond the tip of telson; dorsal two pairs of spines situated at 55% and 70% of telson length; about 10 setae present between inner pair of spines.

Uropodial diaresis ( Fig. 2K View FIGURE 2 ) with movable spine distinct shorter than lateral angle.

Eggs large, oval shaped; full developed eggs (with eyes) measuring 2.3–2.4 x 1.7–1.8 mm.

Sexual dimorphism: Males larger than females (total length: males – 53.8 mm, females – 49.4 mm) with more developed major second pereiopods.

Distribution: M. agwi is only known from the Barobisha Region in Alipurduar District, West Bengal, India.

Body colouration of living specimens: Body mostly reddish brown, grey or light blue in some specimen, with a characteristic pale transverse bar running across the base of the uropodes and the proximal part of the 6 th abdominal segment.

Etymology: M. agwi is named after the “Arbeitsgemeinschaft Wirbellose des Binnenlandes”, abbr. AGW, a German workgroup working on freshwater invertebrates.

Remarks: With regards to the general appearance, the shape and measurements of the second chelipeds M. agw i resembles M. kempi ( Tiwari, 1947) described from Chittagong, Bangladesh. According to the original description ( Tiwari 1947) the most diagnostic morphological character of M. kempi is a dense felt-like hair coat on the inner (lower) margin of the palm of second cheliped which is entire lacking in M. agwi . Furthermore the merus of the male second cheliped seems to be slightly longer in comparison to the carpus in the male type specimen of C. kempi (1.28 vs. 1.14–1.20 in male specimen of M. agwi ). The development of hair coat or spinulation on male second chelipeds depends on the developmental stage of the specimen ( Short 2004). The two large males in the examined collection show well developed densely setose appendix masculina on second pleopods, well developed protective spinulation on carapace and second chelipeds and strongly developed teeth on proximal part of the fingers of major second chelipeds thus seems to be full developed males following the key to male development stages given by Short 2004. Furthermore all four males included in the type series exceed M. kempi in carapace length (13.5–17.4 mm cl vs. 13 mm in M. kempi ).

M. agw i also resembles M. nepalense Kamita, 1974 , described from Tarahara Farm near Itanari, Nepal. Kamita did not compare M. nepalense with M. kempi , but according to his detailed description and drawings these two species seems to be identical.

M. agwi is also near M. altifrons altifrons (Henderson, 1893) first described from river Jamuna near Delhi, India and subsequently (1955, 1963) reported by K. K. Tiwari from several locations in Nepal and East India sharing general appearance, shape of the rostrum and cylindrical second chelipeds not covered with fur with this species. Though the proposed new species can be differentiated from this species by a different shape and armature of second pereiopods. In detail the length of the movable finger is nearly as long (0,9–1,1 times) as the palm in M. agwi vs. more than half as long (half as long or less than half as long in very large males) in M. altifrons . The cutting edge of the movable finger is armed with 2 large teeth in the proximal half of the finger, proximal one triple vs. cutting edge with 5-6 teeth, distalmost located in distal half of the finger, proximal teeth equidistant in M. altifrons . In M. altifrons the inner (lower) margin of the large chela is bearing a longitudinal row of large, somewhat erect spines reaching from base of the palm to tip of the immobile finger in adult specimen which is complete lacking in M. agwi .

With the large egg size, the shape and armature of the rostrum and the telson characteristics M. agwi also resembles M. hendersoni (De Man, 1906) , but could easily distinguished from this species by the relative smooth fingers of second cheliped lacking distinct longitudinal grooves and pappose setal pubescence ( De Man 1907, Tiwari 1955, Cai 2004). Only in large ovigerous females some indistinct dints arranged in rows with scarce setae could be observed on the fingers of the second chelipeds. Moreover M. agwi differs from M. hendersoni in a longer carpus of the major second chelipeds (elongated conical, 0.84–0.88 times as long as merus vs. 0.65–0.77 times as long as merus in M. hendersoni ). M. agwi is also close to M. cacharense ( Tiwari, 1952) , first described as subspecies of M. hendersoni from Assam, India, but can also distinguished from this species and all other members of the M. hendersoni species group by lacking distinct grooves and pubescence in the proximal part of the fingers of male major second chelipeds.