Macrobrachium ngankeeae, Mazancourt & Marquet & Wowor & Keith, 2024

Mazancourt, Valentin De, Marquet, Gerard, Wowor, Daisy & Keith, Philippe, 2024, Macrobrachium ngankeeae, a new species of freshwater shrimp (Crustacea: Decapoda: Palaemonidae) from Papua Barat Province, Indonesia, Zootaxa 5476 (1), pp. 253-266 : 255-259

Macrobrachium ngankeeae n. sp.

( Figs. 2 , 3A )

Type material. Holotype: male (cl 9.7 mm), MZB Cru 5350, Papua Barat Province, Kaimana Regency, Teluk Etna District , Ds. Kayu Merah, Sg. Kayu Merah, 03°53.290’S 134°28.655’E, coll. P. Keith, P. Gaucher, G. Ségura, 22 October 2010 . Paratypes: 1 male (cl 11.3 mm) ( MZB Cru 5781; DNA: MC1226 ) , 1 male (cl 8.2 mm) (MNHNIU-11859; DNA: MC1227 ), Kaimana Regency , Buruway District, Ds. Karawawi, Sg. Kunafa, 04°03.260’S 133°04.742’E, 0–30 m asl, coll. P. Keith, P. Gaucher, G. Ségura, 14 October 2010 ; 1 male (cl 9.7 mm), MZB Cru 5351, 1 ovigerous female (cl 8.7 mm), MNHN-IU-2017-9340, Kaimana Regency , Buruway District , Ds. Karawawi , Sg. Kunafa, 04°03.943’S 133°09.992’E, 77 m asl, coll. P. Keith, P. Gaucher, G. Ségura, 15 October 2010 ; 1 female (cl 9.1 mm), ( MZB Cru 5352; DNA: MC1225 ), Kaimana Regency , Teluk Etna District, Ds. Kayu Merah, Sg. Kayu Merah, 03°53.290’S 134°28.655’E, coll. P. Keith, P. Gaucher, G. Ségura, 22 October 2010 .

Type locality. Rivers in Kaimana Regency , Papua Barat Province, Indonesia .

Diagnosis. A small-sized species with subcylindrical body form. Rostrum short, reaching end of second article to end of third article of antennular peduncle; dorsal margin slightly convex, rostral formula: 3–4+6–8/2–3, dorsal teeth subequally spaced; first tooth at 0.23–0.27 anterior of cephalothorax. Carapace glabrous. Ocular beak moderately developed. Third maxilliped with exopod shorter than ischiomerus. T4 with median process. Second pereiopods robust, rather long, dissimilar in shape, unequal in size, covered with squamiform setae. Major second pereiopod chela with compressed palm, no setae on cutting edge of fingers, dentate on opposable margins, slightly gaping, fingers shorter than palm, distal part of dactylus and pollex with double row of tubercles each. Cutting edges of minor second pereiopod gaping, densely covered with long stiff setae concealing surface, fingers as long as to longer than palm. Carpus conical, shorter than chela, shorter than palm, slightly shorter than merus. Third, fourth and fifth pereiopods glabrous, with few scattered short stiff setae. Pre-anal carina well developed. Uropods glabrous, exopod with mobile mesial spine as long as distolateral tooth. Developed eggs small, maximum size 0.6 × 0.5 mm, ovoid, numerous.

Description of holotype and paratypes (in parentheses).

Cephalothorax. Rostrum short, 0.36 cl (0.37–0.43 cl in paratypes), reaching end of second article to end of third article of antennular peduncle ( Fig. 2I ); moderately slender, maximum depth 0.75 times as maximum dorsoventral diameter of cornea; lateral carina well developed, continuing almost to tip; dorsal carina convex, bent downwards in front of orbit with tip directed anteriorly, armed with 11 (10–12) subequally spaced teeth, interspaces setose, 4 (3 or 4) teeth completely postorbital, first postorbital tooth on anterior 0.24 (0.23–0.27) of carapace; ventral carina convex with 3 (2 or 3) teeth, first tooth located at about one-third distal. Carapace glabrous; inferior orbital margin moderately produced, obtuse, postantennular carapace margin evenly rounded; antennal spine sharp, slender, continuing posteriorly as ridge, situated below lower orbital angle; hepatic spine smaller, situated behind and below antennal spine. Ocular beak moderately developed without expanded lateral tip; cornea well developed 0.18 (0.18– 0.22) carapace length, well pigmented.

Epistome ( Fig. 2F ), bilobed, separated by a wide rather shallow depression anteriorly, lobes with rounded anterior margin.

Thoracic sternum, T4 with small median process, with distinct submedian plate; T8 with contagious anterolateral lobes (in fully developed male), with large shallow conical median process.

Antennular peduncle 0.38 (0.43–0.51) carapace length; basal article with sharply pointed stylocerite ( Fig. 2I ), reaching middle second article of antennular peduncle.

Scaphocerite ( Fig. 2G, I ), stout, reaching beyond rostrum, 0.57 (0.47–0.51) carapace length, length 3.44 (2.04–2.80) maximum width, lamina distinctly tapering from broadest point to anterior margin, outer lateral margin straight, inner lateral margin concave, distolateral tooth reaching end of lamella.

Third maxilliped with exopod shorter than ischiomerus. Mouthparts typical of the genus.

First pereiopods slender, equal in length and similar in form ( Fig. 2D ), 1.41 (1.06–1.33) carapace length, exceeding scaphocerite by chela and distal half of carpus; fingers 0.61 (0.59–0.77) palm length, carpus 1.48 (1.13– 1.53) chela length, carpus 1.19 (1.00–1.34) merus length; scattered short stiff setae present on chela, scattered long stiff setae present on half proximal merus, and a long inners margin of ischium and base, otherwise glabrous.

Second pereiopods dissimilar in shape and size, robust, covered with squamiform and mammiliform modified setae, larger and more developed in adult sub-dominant and dominant males than females.

Male major cheliped ( Fig. 2A ): chela 1.14 (0.83–1.17) carapace length, length 2.09 (1.37–2.83) times width, outer and inner margins convex, palm compressed; ventral, outer and dorsal margins with pliable squamiform modified setae, inner margin with blunt stiff modified mammiliform setae, inner margin modified setae largest than those on other margins; fingers ( Fig. 2B ) 1.02 (0.63–0.79) times palm length, slightly gaping, with uncinate tip; dactylus with 3 increasing size teeth at proximal, followed by unarmed edge ending in a triangular tooth at about two-third proximal, rest distal part of dactylus with a raw of small tubercles on inner and outer cutting edge each, outer and inner dactylus with 2 (2) and 2 (1–2) tubercles respectively; pollex cutting edge has similar tooth arrangement as those on dactylus, 4 teeth at about one-third proximal, largest at most end of row, a triangular tooth at about half pollex, rest distal part of pollex with a raw of small tubercles on inner and outer cutting edge each, outer and inner pollex with 3 (3) and 2 (1–3) tubercles respectively; palm width distinctly greater than maximum carpus width and merus width; chela 1.95 (2.09–2.5) carpus length; carpus 1.04 (0.68–0.86) palm length, conical, length 1.78 (1.69–2.16) times width, 1.04 (0.92–1.23) times merus length, merus 1.45 (1.13–1.52) times ischium length.

Male minor cheliped ( Fig. 2C ): cheliped length 0.86 (0.92–0.93) major cheliped, chela with outer and inner margins slightly convex to almost straight, palm cylindrical; outer margin with few scattered small pliable squamiform modified setae, smaller than those on major chela, inner margin with minute blunt stiff modified mammiliform setae, armed with squamiform setae on all articles, fingers 1.55 palm length, slightly gaping, both cutting edges with few tufts stiff setae; proximal dactylus with 2 small teeth, proximal pollex with 2 small teeth; palm length 1.21 times width; carpus 1.03 times palm length, conical, length 2.05 times width, 0.39 times chela length, 0.93 times merus length, merus 1.26 ischium length.

Female major cheliped: ventral, outer and dorsal margins densely covered with pliable squamiform modified setae, inner margin with blunt stiff modified mammiliform setae, inner margin modified setae largest than those on other margins; chela 0.86 carapace length; fingers 0.74 palm length, not gaping, with uncinate tip; cutting edge of dactylus with 3 increasing size teeth at proximal; cutting edge of pollex with 5 increasing size teeth at proximal; palm cylindrical, length 1.76 times width; carpus long conical, 0.88 times palm length, length 2.26 times width, 0.88 times chela length, 1.00 times merus length, merus 1.61 ischium length.

Female minor cheliped. Ventral, outer and dorsal margins densely covered with pliable squamiform modified setae, inner margin with blunt stiff modified mammiliform setae, inner margin modified setae largest than those on other margins; chela about as long as major chela; fingers 0.70–0.85 palm length, both cutting edges with densely tufts stiff setae, no tooth; palm cylindrical, length 2.59–2.63 times width; carpus 0.80–0.87 palm length, long conical or semi-subcylindrical, length 2.69–2.81 times width, 0.47 times chela length, 0.49 times merus length, merus 1.16–1.23 times ischium length.

Third pereiopods. Few scattered short stiff setae present on all articles; dactylus stout, curved, fringed with dorsolateral setae; propodus 3.12–3.67 times dactylus length, 6.59–6.77 times width, 5–7 ventral spines distributed along propodus, 2 distal most spines paired; carpus 0.53–0.59 times propodus length; merus 1.02–1.05 times propodus length, 1.89–2.43 times ischium length.

Fifth pereiopods ( Fig. 2E ). Few scattered short stiff setae present on all articles; dactylus stout, curved; propodus fringed with a row ventrolateral setae at distal end, length 7.93 (8.34–8.46) times width, propodus 4.23 (3.63–4.29) times dactylus length, 5 or 6 ventral spines distributed along propodus; carpus 0.52 (0.57–0.59) as long as propodus; merus 0.80 (0.77–1.00) as long as propodus, 1.72 (1.59–2.48) as long as ischium.

Abdomen. Smooth, glabrous; sixth somite 1.34 (1.30–1.65) times as long as fifth somite. Male with first two abdominal sternites with triangular median process; lateral margin of process on first and second sternites sloping ca. 70° from horizontal; process on second sternite similar in form and size as on first sternite, third sternite without process. Inter-uropodal sclerite well developed as longitudinal pre-anal carina, carina large-sized.

Pleopods. Endopod of first pleopod kidney-shape with inner margin concave, outer margin convex, apex rounded, reaching 0.29–0.41 exopod length, without appendix interna.

Male second pleopod with appendix masculina long, slender, rod-shaped, reaching 0.59 endopod length, with numerous stiff simple setae on anterior margin; appendix interna reaching 0.51 appendix masculina length.

Uropods. Surface glabrous, exopod with mobile mesial spine as long as or larger than distolateral tooth.

Telson ( Fig. 2H ). Elongated, stout, 1.46 (1.28–1.88) times sixth abdominal somite, length 3.13 (2.44–3.06) times median width, lateral margins straight, convergent, 2 pairs of dorsal spines present, posterior margin triangular with large rounded median point, median projection overreached by inner pair of posterior spines, inner pair of posterior spines 2.7 longer than outer pair, with 9–13 pairs of long plumose subventral setae exceeding inner pair of spines and apex of telson.

Reproductive biology. Ovigerous female with numerous small-sized eggs. Eggs oval, diameter 0.62– 0.52 mm × 0.42–0.48 mm. The number and size of the eggs are indicative of prolonged larval development, which belongs to amphidromous species ( Wowor et al. 2009).

Life color. Mainly translucent grey, with mottled pattern of gold-white and darker spots scattered especially on cephalothorax and walking legs; pleon, telson and uropods translucent ( Fig. 3A ).

Notes on habitat. Macrobrachium ngankeeae n. sp. is an inhabitant of moderate to rather fast flowing rivers in coastal lowland. This new species is found at elevation from below 5 to 30 m ( Fig. 3B ).

Distribution. This new species is so far known only from southern lowlands in West Papua Province, Indonesia.

Etymology. The late Ng Ngan Kee (14 April 1966 to 5 July 2022) was a leading taxonomist of brachyuran crabs, especially of the family Varunidae . She was a good friend and ex-lab mate of the third author (DW), and a very kind-hearted person, who always gave her help whenever needed. The present new species, Macrobrachium ngankeeae , n.sp., is dedicated to her memory. The specific epithet refers to her first combined name, Ngan Kee, the name by which most of her colleagues and friends addressed her.

Remarks. Genetic analyses ( Fig. 1 ) and morphological examinations ( Table 1 ) show that Macrobrachium ngankeeae sp. nov. belongs to M. placidulum species group ( Saeki et al. 2018). Keith & Vigneux (2002) also mentioned that M. feunteuni resembled M. lepidactyloides . Therefore, both M. ngankeeae n. sp. and M. feunteuni are included in the M. placidulum species group in the present study. The new species, however, is distinct from M. lepidactyloides by having 3 or 4 postorbital teeth (vs 5–7) with the first tooth placed in the anterior 0.23–0.27 of the cephalothorax (vs 0.47–0.55), the fingers of the minor second pereiopod of adult males equal to moderately longer than the palm 0.97–1.49 (vs 1.75–2.12), and the T4 has a small median process (vs no median process).

Overall, Macrobrachium ngankeeae n. sp. resembles M. placidulum , in which the second pereiopods of males are dissimilar in form and of unequal size, and are covered by modified squamiform setae. However, M. ngankeeae n. sp. differs by having fewer postorbital teeth (3–4 vs 4–6) and the more anterior position of the first tooth at the cephalothorax (0.23–0.27 vs 0.29–0.50), prominent ocular beak (vs absent or poorly developed), minor second pereiopod fingers in adult males that are as long as to moderately longer than the palm length (vs fingers slightly shorter to about as long as palm), and a small median process present on T4 (vs no median process).

Macrobrachium ngankeeae n. sp. is similar to M. placidum . However, M. ngankeeae n. sp. can be recognized by having 3 or 4 postorbital teeth (vs 5–7), with its first tooth placed in 0.23–0.27 of the cephalothorax (vs 0.46– 0.49), shorter major second pereiopod fingers compared to palm length in adult males (0.63–0.72 vs 0.90–1.38), and a small median process present on T4 (vs no median process).

Macrobrachium ngankeeae n. sp. also resembles M. feunteuni , but both species can be easily differentiated. The new species has a flat and straight rostral dorsal margin above the eyes (vs slightly convex), rostrum with 3 or 4 postorbital teeth (vs 6–7), longer major second pereiopod chela compare to the carpus in adult males (2.38–3.18 vs. 1.57–2.33), and small median process on T4 (vs. no median process).

Figures

FIGURE 1. 16S Bayesian phylogenetic tree of Macrobrachium placidulum species-group. Numbers above branches are Bayesian posterior probabilities, numbers under branches are bootstrap values.

FIGURE 2. Macrobrachium ngankeeae n. sp., holotype male, cl 9.7 mm, MZB Cru5350, Papua Barat Province: A, major second pereiopod; B, major second pereiopod fingers; C, minor second pereiopod; D, first pereiopod; E, fifth pereiopod; F, epistome; G, scaphocerite; H, telson; I, cephalothorax.

FIGURE 3. A, living male specimen of Macrobrachium ngankeeae n. sp.; B, typical habitat of M. ngankeeae n. sp. (photos by P. Keith).