Macrobrachium heterorhynchos, Guo & He, 2008

Guo, Zhao-Liang & He, Shun-Lian, 2008, One new and four newly recorded species of the genus Macrobrachium (Decapoda: Caridea: Palaemoindae) from Guangdong Province, southern China, Zootaxa 1961 (1), pp. 11-25 : 12-16

publication ID	https://doi.org/ 10.11646/zootaxa.1961.1.2
DOI	https://doi.org/10.5281/zenodo.5242534
persistent identifier	https://treatment.plazi.org/id/3936E522-D05B-FFB5-FF0F-FDA4FB0DFCCF
treatment provided by	Felipe
scientific name	Macrobrachium heterorhynchos
status	sp. nov.

Treatment

Macrobrachium heterorhynchos View in CoL sp. nov.

( Figs. 1 View FIGURE 1 , 2 View FIGURE 2 , 7A, B View FIGURE 7 )

Material examined. Holotype: adult male ( FSTC, 02–06–11–01), tl. 65.4 mm, cl. 15.4 mm, rl. 14.8 mm, Xijiang river near Jiangmen City (ca. 22°33’N, 113°08’ E), 11 June 2002. GoogleMaps

Paratypes: 3 males ( FSTC, 02–06–11–02 to 04), tl. 64.8–71.0 mm, cl. 14.1–16.9 mm, rl. 14.0–16.0 mm; 1 ovigerous female ( FSTC, 02–06–11–05), tl. 76.7 mm, cl. 19.8 mm, rl. 14.0 mm ; 1 female ( FSTC, 02–06–11– 06), tl. 58.2 mm, cl. 15.3 mm, rl. 10.9 mm; data same as holotype GoogleMaps .

Diagnosis. Rostrum sexually dimorphic, very long in males, about one-third distal extending beyond scaphocerite, tip strongly curved upwards, rl. about as long as cl.; rostral formula: 3 + 8–9/4, dorsal teeth unequally spaced, usually with wide gaps near posterior and anterior ends of series; in females, rostrum just reaching end of scaphocerite, rl. about 0.7 cl., upper margin slightly convex above eyes, tip slightly curved upwards, rostral formula: 3 + 8/5, distribution of dorsal teeth similar to of males. Cephalothorax and abdomen smooth, without microspinules. Second pereiopods shorter than tl. in both sexes, equal, ischium as long as merus, carpus about 1.4 as long as merus, and shorter (0.7–0.8 times) than chela, longer (1.2–1.6 times) than palm, fingers of males about as long as palm, fingers of females shorter (0.7–0.8 times) than palm; cutting edge of both fingers with 2 teeth. All segments covered with numerous microspinules except for ischium. Egg size: 0.50–0.59 × 0.61–0.69 mm in diameter.

Description. Rostrum ( Figs. 1A, B View FIGURE 1 , 7A, B View FIGURE 7 ) with distinct sexual dimorphism, rostrum of males very long, distal 1/3 extending beyond scaphocerite, tip strongly curved upwards, rl. about as long as cl.; dorsal margin with 11 or 12 teeth, 3 teeth behind orbit, unequally spaced, usually with wide gaps near posterior and anterior ends of series; ventral margin with 4 teeth. Females with rostrum just reaching end of scaphocerite, rl. about 0.7 cl., upper margin convex above eyes, tip slightly curved upwards with 11 dorsal teeth, ventral margin 5 teeth, teeth distribution similar to that of males.

Carapace ( Figs. 1A, B View FIGURE 1 , 7A, B View FIGURE 7 ) glabrous; antennal spine well developed; hepatic spine much smaller than antennal spine, and lies in the same line with the latter.

Antennule ( Fig. 1A, C View FIGURE 1 ) with sharp stylocerite, reaching one-third basal segment of antennular peduncle; anterior margin of basal segment distinctly convex; second segment about 0.45–0.55 times as long as basal segment, about 1.1–1.2 time as long as distal segment. All segments with submarginal plumose setae.

Antenna ( Fig. 1A, D View FIGURE 1 ) with large scaphocerite, rectangular, 2.8–3.1 times as long as wide, outer margin almost straight, ended with a strong spine, overreached by lamella.

Mandible ( Fig. 2A View FIGURE 2 ) with 3-segmented palp; incisor process with 3 sharp teeth; molar process stout, distally excavated, with blunt teeth and ridges.

Maxillula ( Fig. 2B View FIGURE 2 ) with bilobed palp, upper lobe slender, setose distally, lower lobe stout, hooked; upper lacinia broadly elongated, distal margin with row of strong spines, lower lacinia as long as upper lacinia, densely setose distally.

Maxilla ( Fig. 2C View FIGURE 2 ) with simple palp; basal endite deeply bilobed, upper and lower lobes with numerous simple setae distally; scaphognathite broad, about 3.4 times as long as wide.

First maxilliped ( Fig. 2D View FIGURE 2 ) with subcylindrical, distally tapering palp, basipodal and coxal endites distinct; exopod with large caridean lobe, flagellum with numerous plumose setae distally, epipod deeply bilobed, upper lobe triangle, lower lobe oval.

Second maxilliped ( Fig. 2E View FIGURE 2 ) with normal endopod, last segment fused with entire length of penultimate; exopod well developed, flagellum with plumose setae distally, epipod simple, with well-developed podobranch.

Third maxilliped ( Fig. 2F View FIGURE 2 ) with robust endopod, ischiomerus slightly bow-shaped, with rows of long simple setae on distal inner and outer margins; carpus about 0.76 times length of ischiomerus, with row of long, simple setae on inner margin and sparse row of simple setae on outer margin; distal segment about 0.78 times penultimate segment, with long, simple setae on inner margin; exopod reach distal end of ischiomerus, with plumose setae distally; basal with well developed oval lateral plate, two arthrobranchs, one rudimentary, obscured by the larger.

Branchial formula typical for genus.

First pereiopods ( Figs. 1A View FIGURE 1 , 2G View FIGURE 2 ) slender, base of fingers extending beyond scaphocerite, carpus 1.8–2.1 times as long as chela; palm shorter than fingers.

Second pereiopods ( Fig. 1A, E View FIGURE 1 ) slightly shorter than the tl. in both sexes, similar in shape and size, distal merus extending beyond scaphocerite; the finger 0.71–0.97 times as long as palm, fixed finger with 2 teeth at proximal, basal tooth is formed of 2–3 denticles, moveable finger with 2 proximal teeth, palm not inflated, 4.0–4.6 times as long as width; carpus is 6.6–8.8 times as long as width, 1.2–1.6 times as long as palm, and is 1.4–1.6 times as long as merus; merus of males slight longer than palm, 1.0–1.2 times as long as palm, in females merus shorter than palm, 0.8–0.9 times as long as palm; merus 1.1 times as long as ischium; all segments covered with numerous microspinules except for ischium.

Third pereiopods ( Figs. 1A View FIGURE 1 , 2H View FIGURE 2 ) extending beyond scaphocerite by one-fifth distal propodus; propodus 2.2–2.6 times as long as dactylus, dactylus about 6.0 times as long as width, terminating in a small claw.

Fifth pereiopods ( Figs. 1A View FIGURE 1 , 2I View FIGURE 2 ) extending beyond tip of scaphocerite; propodus 3.0–3.3 times as long as dactylus, dactylus about 5.4 times as long as width, terminating in a small claw.

First pleopods of male with endopod of about half of exopod, slightly concave at inner margin, top rounded, without appendix interna.

Second pleopods with well developed appendix masculina, reaching middle of endopod, about twice as long as appendix interna with numerous stiff setae.

Abdomen ( Figs. 1A View FIGURE 1 , 7A, B View FIGURE 7 ) glabrous; pleura of first three somites broadly rounded, pleura of somites 4 and 5 also rounded, but with almost rectangular posterolateral angle; sixth somite 1.2–1.6 times as long as fifth somite, about 0.6–0.7 times as long as telson.

Telson ( Fig. 1A, F View FIGURE 1 ) smooth, about 0.6 times cl., longer than sixth abdominal segment; dorsal surface furnished with 2 pairs of stout movable spines; posterior margin tapers regularly to a sharp point with 2 pairs of posterior spines; numerous setae present between inner spines.

Uropodal diaeresis with a spine, shorter than outer angle.

Eggs small, 0.50–0.59 X 0.61–0.69 mm in diameter.

Live coloration. All specimens light green with numerous small reddish spots on carapace, abdomen and uropods. Third abdominal somite with a white broad transverse band near posterior margin. Endopod of third maxilliped transparent, distal segment entirely reddish, penultimate segment with 3 red rings, basal segment with 1 red ring; ischium, merus and fingers of second pereiopods translucent, with 3, 4 and 2 red rings respectively, outer surface of carpus and palm yellowish, with 2 longitudinal dark stripes near margins (these dark stripes persist in preservation, Fig. 7A, B View FIGURE 7 ). First, third, fourth and fifth pereiopods transparent, ischium, merus and carpus with 2, 4 and 2 red rings respectively, half proximally of fingers reddish; a large dark spot on uropods; eggs reddish brown.

Etymology. Species name is derived from heteros (Greek), meaning different and rhynchus (Greek), meaning nose in reference to the rostral morphology of the male being different from the female.

Remarks. Macrobrachium heterorhynchos superficially resembles M. inflatum Liang & Yan, 1985 , in having similar ratios of various segments of the second pereiopods. However, it can be distinguished from M. inflatum by its sexually dimorphic rostrum (versus non-sexually dimorphic); the palm of the male second pereiopods is not inflated (versus inflated) and 4.0–4.6 times (versus 3.5–3.6 times) as long as broad, the merus is distinctly longer than the palm or the ischium (versus shorter than the palm or the ischium), the cutting edge of the fixed finger bears two teeth (versus one tooth), without a gape present when closed (versus with a distinct gape present); the scaphocerite is broader (the length is 2.8–3.1 times as long as width versus 3.4 times); and they have entirely different body coloration.

Macrobrachium heterorhynchos is also close to M. nipponense (De Haan, 1849) . Comparison of adult specimens of equivalent size to M. heterorhynchos and specimens of M. nipponense from Guangdong province shows that it can be distinguished from latter by characters of rostrum and second pereopods. The rostrum of M. heterorhynchos is sexual dimorphic (versus non-sexual dimorphic) and with more ventral teeth (4 or 5 versus 2 or 3). The second pereiopods of M. heterorhynchos are distinctly shorter than those of M. nipponense ; the merus is distinctly longer than the palm (versus shorter than the palm), the finger is proportionally longer in M. heterorhynchos than in M. nipponense (ratio of finger to palm length 0.71-1.0 versus 0.6- 0.7), and without setae on cutting edge (versus covered with long dense setae).

Habitat:

The type specimens were collected from near Jiangmen City (ca. 22°33’N, 113°08’ E). The locality is approximately 50 km away from the northern coast of Nanhai Sea. The water is brackish with temperature 26°C and pH 7.5. It is found together with M. nipponense and M. hainanense .

Distribution. Known only from the type locality in Guangdong Province, southern China.