Macrobrachium saengphani, Saengphan & Panijpan & Senapin & Laosinchai & Suksomnit & Phiwsaiya, 2020

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), pp. 531-542 : 534-536

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.

Figures

FIGURE 2. Male (upper and smaller) and female (lower and larger) Macrobrachium saengphani sp. nov.

FIGURE 3. Macrobrachium saengphani sp. nov. (male). (A) Entire animal, lateral view; (B) telson; (C) scaphocerite; (D) epistome; (E) mandible; (F) maxillula; (G) maxilla; (H) first maxilliped; (I) second maxilliped; (J) third maxilliped; (K) first pereiopod; (L) second pereiopod; (M) chela; (N) third pereiopod; (O) movable spine. Scales: (A) 5 mm; (B, C, E–N) 1 mm, (D) 0.5 mm, (O) 0.1 mm.

FIGURE 4. Stiff setae on cutting edge of finger of second pereiopod of female (upper) and male (lower) Macrobrachium saengphani sp. nov.

FIGURE 5. Phylogenetic tree containing Macrobrachium saengphani sp. nov. reconstructed from mitochondrial COI and nuclear 18S genes using partitioned Bayesian inference with Cryphiops caementarius and Coralliocaris superba constituting an outgroup. The numbers at the nodes represent the posterior probabilities supporting the corresponding clades. Branch lengths and (horizontal) heights of isosceles triangles represent the estimated numbers of nucleotide substitutions per site.

FIGURE 6. Golden antennules of Macrobrachium saengphani sp. nov.

FIGURE 7. Rostrum of Macrobrachium saengphani sp. nov.