Macrobrachium dongaoensis, Chen & Chen & Guo, 2018

Chen, Qing-Hua, Chen, Wen-Jian & Guo, Zhao-Liang, 2018, Caridean prawn (Crustacea, Decapoda) from Dong'ao Island, Guangdong, China, Zootaxa 4399 (3), pp. 315-328 : 323-327

Macrobrachium dongaoensis sp. nov.

( Figs. 7–9 )

Material examined. Holotype. Adult male (FU, 17–06–23–01), tl: 79.0 mm, cl: 19.5 mm, rl: 12.0 mm; Dong’ao island , Zhuhai City , Guangdong Province (E 113°43'09", N 22°01'08", al. 22.4 m, stn.7), 26 Jun 2017, coll. Z. L. Guo, W. J. Chen.

Paratypes. 1 male (FU, 17–06–23–02), tl: 73.7 mm, cl: 19.3 mm, rl: 10.5 mm; 1 ovigerous female (FU, 17– 06–23–03), tl: 67.0 mm, cl: 18.0 mm, rl: 12.0 mm, data same as holotype .

Diagnosis. Rl is about 0.54–0.67 of cl, nearly straight, falling slightly short of anterior end of antennal scale, dorsal margin with 10–13 teeth, 4 or 5 (usually 4) teeth behind orbit, equally spaced, ventral margin with 1–3 teeth. Cephalothorax and abdomen smooth, without microspinules. Second pereiopods shorter than tl in both sexes, subequal in length in male, the right slightly longer, but equal in female; merus is about 1.1 times as long as ischium; carpus is 4.4–5.4 times as long as width, about 1.1–1.4 times as long as merus and almost same length of palm; palm is not inflated, 4.3–4.9 times as long as wide; the finger 0.69–0.78 times as long as palm, fingers without gape when crossed, the fixed finger with 2 teeth at proximal, moveable finger with 2 proximal teeth; all segments are covered with numerous spines particularly on dorsal and lateral surfaces. Eggs small, 0.33–0.42 X 0.37–0.44 mm in diameter.

Description. Rostrum. ( Fig. 7a ) Rl is about 0.54–0.67 of cl, nearly straight, reaching to or slightly beyond end of scaphocerite, dorsal margin with 10–13 teeth, 4 or 5 (usually 4) teeth behind orbit, equally spaced, ventral margin with 1–3 teeth.

Carapace. ( Fig. 7a ) Glabrous; antennal spine well developed; hepatic spine much smaller than antennal spine, situated backwardly, distinctly below level of antennal spine.

Antennule. ( Fig. 7a ) with sharp stylocerite, reaching one–third basal segment of antennular peduncle; anterior margin of basal segment distinctly convex; second segment about 0.45 times as long as basal segment, about 0.81 time as long as distal segment. All segments with submarginal plumose setae.

Antenna. ( Fig. 7a ) with scaphocerite large, rectangular, 3.4 times as long as wide, outer margin almost straight, ended with a strong spine, overreached by lamella.

Third maxilliped with robust endopod, ischiomerus slightly bow-shaped, with rows of long simple setae on distal inner and outer margins; carpus about 0.75 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 0.81 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.

First pereiopod. ( Fig. 7b ) Slender, overreaching antennal scale by carpus, carpus 1.7–1.9 times as long as chela; fingers as long as palm.

Second pereiopod. ( Fig. 7c, d ) Slightly shorter than the tl in both sexes, subequal in length in male, the right slightly larger, extending beyond antennal scale by 1/2 carpus, equal in female; the shape and segment ratios of the left and the right are similar; merus is about 1.1 times as long as ischium; carpus is 4.4–5.4 times as long as width, about 1.1–1.4 times as long as merus and almost same length of palm; palm is not inflated, 4.3–4.9 times as long as wide; the finger 0.69–0.78 times as long as palm, fingers without gape when crossed, the fixed finger with 2 teeth at proximal, moveable finger with 2 proximal teeth; all segments are covered with numerous spines particularly on dorsal and lateral surfaces.

Third pereiopod. ( Fig. 7e ) Extending to end of third antennular peduncle segment by distal propodus; propodus 2.8–3.0 times as long as dactylus, with 5–7 spines on posterior margin, dactylus about 5.0 times as long as width, terminating in a claw.

Fifth pereiopod. ( Fig. 7f ) Extending to end of third antennular peduncle segment; propodus 3.4–4.3 times as long as dactylus, with 4 spines on posterior margin, dactylus about 5.3 times as long as width, terminating in a small claw.

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

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

Abdomen glabrous; pleura of first three somites broadly rounded, pleura of somites 4 and 5 also rounded, but with almost rectangular posterolateral angle; sixth somite 1.2–1.4 times as long as fifth somite, about 0.40–0.43 times as long as telson.

Telson. ( Fig. 7g ) Smooth, about 0.62–0.72 times of cl, longer than sixth abdominal segment; dorsal surface 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, 0.33–0.42 X 0.37–0.44 mm in diameter.

Live coloration. The live specimens ( Fig. 8a, b ) are light green and translucent, uropod with numerous small reddish spots uropods; all segments of second pereiopods is brown, with one dark rings on outer posterior surface on merus and two dark rings on carpus, the palm have two longitudinal dark stripes near margins; first, third, fourth and fifth pereiopods transparent; eggs green ( Fig. 8b ).

Etymology. The new species is named after its distribution area, Dong’ao Island.

Remarks. Macrobrachium dongaoensis superficially resembles M. inflatum Liang & Yan, 1985 in having similar ratios of various segments of the second pereiopods and breeding female bears smaller sized numerous eggs. However, it can be distinguished from M. inflatum by its shorter rostrum (extending to end of third antennular peduncle segment versus beyond antennal scale; rl<cl versus rl=cl); the male second pereiopods are subequal (versus equal), the right slightly longer, the palm is not inflated (versus inflated) and 4.3–4.9 times (versus 3.5–3.6 times) as long as broad, the merus is distinctly longer than the ischium (versus shorter than the ischium), without a gape present when closed (versus with a distinct gape present).

M. dongaoensis morphologically resembles M. heterorhynchos Guo & He, 2008 , which was originally described also from Guangdong Province. It can be distinguished from M. heterorhynchos by the shorter (reaching to end of scphocerite versus one–third distal 1/3 of rostrum extending beyond scaphocerite) and non-sexually dimorphic rostrum (versus sexually dimorphic); the carpus of male second pereiopods is as long as palm (versus distinctly longer than the palm).

M. Dongaoensis is also close to M. nipponense (De Haan, 1849) . It can be distinguished from latter by characters of the male second pereopods. The second pereiopods of M. Dongaoensis are distinctly shorter than those of M. nipponense ; the carpus is as long as palm (versus distinctly longer than the palm). and the finger without setae on cutting edge (versus covered with long dense setae).

Habitat. The type specimens were collected from Dong’ao Island, Zhuhai City, Guangdong Province (E 113°43'09", N 22°01'08", al. 22.4 m). This stream (Fig, 9) is biggest in Dong’ao Island, which with the width of about 4 m, deepth about 0.5–0.8 m, with beds of sand and gravel patches between large boulders, and with full of bank vegetation and spirogyras. It is a moderately fast stream, flows into the sea. It is found together with Caridina serrata .

Distribution. Only known from the type locality in Guangdong Province, southern China.

Figures

FIGURE 8. Macrobrachium dongaoensis, new species, live specimen, showing the characteristic colouration, a, male, dorsal viewand, cl. 19.3 mm; b, ovigerous female, lateral view, cl.18.0 mm.

FIGURE7. Macrobrachiumdongaoensis, new species. a. cephalothorax and cephalic appendages, lateral view, holotype,male (FU, 17–06–23–01), cl: 19.5 mm; b. first pereiopod; c. second pereiopod; d. palm and fingers of second pereiopod; e.third pereiopod; f.fifth pereiopodd; g. posterior portion of telson.Scale:2 mm.

FIGURE 9. Macrobrachium dongaoensis, new species, type locality, stn.7.