Macrobrachium formosense Bate, 1868

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 : 16-18

Macrobrachium formosense Bate, 1868

( Figs.3 , 7C )

Macrobrachium formosense Bate, 1868: 364 , fig. 1, pl. 31 [type locality: Tansui, northern Taiwan]; Holthuis, 1950: 156; Shokita, 1979: 207; Suzuki et al., 1993: 58; Shy & Yu, 1998: 25; Li et al., 2007:93.

Palaemon similis Yu, 1931: 281 , fig. 2.

Macrobrachium hainanense Holthuis, 1950: 158 , fig. 35; Liu et al., 1990: 118, fig. 15; Chace & Bruce, 1993: 27.

Material examined. 3 females, tl. 61.0– 71.6 mm, cl. 18.2–26.0 mm, 4 males, tl. 61.8– 93.0 mm, cl. 21.3–29.8 mm, near Dongan Town , Zhuhai City, 12 July 2002 ; 2 females, tl. 35.1–55.5 mm, cl. 9.5–19.6 mm, 3 males, tl. 45.2–65.3 mm, cl. 11.8–27.0 mm, Dingjia Bay , Jinwan District, Zhuhai City, 13 July 2002 ; 4 females, tl. 45.4– 51.1 mm, cl. 11.0– 19.6 mm, 5 males, tl. 38.5–78.3 mm, cl. 8.7–29.1 mm, near Shantou City , 16 April 2003 ; 2 females, tl. 45.3–56.1 mm, cl. 12.0– 23.2 mm, 3 males, tl. 48.0– 67.4 mm, cl. 12.8–23.2 mm, near Yangjiang City , 18 May 2003 ; 2 females, tl. 75.0– 73.5 mm, cl. 25.5–27.2 mm, 8 males, tl. 80.1–97.6 mm, cl. 24.5–32.2 mm, near Guangning County, 10 July 2004 . 1 female, tl. 55 mm, cl. 12.5, 4 males, tl. 70.5–89.0 mm, cl. 21.2– 30.5 mm, Xiachuan Island , Taishan City, 18 July 2008 .

Diagnosis. Rostrum reaching to end of antennular peduncle, upper margin slightly convex above eyes, rostral formula: 3–4 + 9–10/2–4, rl. about 0.55–0.66 times cl. Cephalothorax, abdomen and telson roughened, with numerous microspinules, densest laterally. Second pereiopods of adult male stout, equal or subequal in size, all segments rough, covered with microspinules, finger about 0.50–0.60 times as long as palm, cutting edges of both fingers with 2 or 3 teeth, basal tooth of fixed finger formed of 2 or 3 denticles; carpus longer or as long as palm, palm 4.9–6.8 times as long as width; carpus about 1.4–1.6 times as long as merus; merus about 1.3–1.6 times as long as ischium ( Fig. 3 ). Egg size: 0.42–0.55 X 0.52–0.69 mm in diameter.

Description. Rostrum ( Fig. 3A ) exceeding the end of antennular peduncle, not reaching beyond the end of scaphocerite; rl. is about 0.55–0.66 times of cl.; upper margin slightly convex over eyes; 12–14 dorsal rostral teeth, of which 3 or 4 teeth placed behind the orbit. Distance between first dorsal tooth and orbital margin 0.29 cl. The distance between the first and second tooth is about 1.5 times of the second and third tooth. There are 3 ventral rostral teeth. The scaphocerite ( Fig. 3B ) is large, is about 3.0 times as long as broad, with a distinct spine near the outer part of the base.

First pereiopod ( Fig. 3A ) slender, reaching 1/3 of carpus length beyond scaphocerite. Carpus about 2.6 times length of chela; palm longer than the fingers. Second pereiopod ( Fig. 3A ) very strong in adult male, subequal in size, shape and segment ratios of left and right similar. Merus about 1.3–1.6 times as long as ischum; carpus about 1.4–1.6 times as long as merus and almost same length as palm; palm 4.9–6.8 times as long as wide; dactylus about 0.5–0.6 times as long as palm. Cutting edge of both fingers with 2 teeth, situated at proximal one-third. All segments covered with numerous spines and scattered setae. Last three pereiopods ( Fig. 3A ) slender. Dactylus of fifth leg reaching about 1/3 of scaphocerite, propodus about 2.8 times as long as dactylus.

Abdomen ( Fig. 3A ) rough, with numerous small spinules on pleura; uropods with numerous small spinules on surface. Sixth somite about 1.6 times as long as the fifth and 0.65 times as long as telson. Telson ( Fig.3A,C ) rough, covered with numerous small spinules on dorsal surface, about 0.5 cl., distinctly longer than sixth abdominal segment; dorsal surface with 2 pairs of stout movable spines; posterior margin tapering regularly to a sharp point and with 2 pairs of posterior spines; numerous setae present between inner spines.

Remarks. This species is very easily confused with M. hainanense ( Parisi, 1919) . Holthuis (1950) showed that Palaemon similis Yu, 1931 , is a synonym of M. hainanense . Since then, M. formosense is only known from Taiwan, while on the mainland, M. hainanense was the name used by local carcinologists ( Liu 1957; Dai 1984; Liu et al. 1990). In the present study, we examined large numbers of specimens from Guangdong Province. The results show that M. formosense can be differentiated from M. hainanense by the structure and proportions of the segments of the male second pereiopods and the tooth arrangement on the cutting edge of the fingers. In M. formosense , the second pereiopods are equal or subequal, the carpus is longer or sometimes as long as the palm, and the basal tooth of the fixed finger is formed of 2 or 3 denticles, while in M. hainanense the second pereiopods are equal in length, the carpus is distinctly shorter than the palm, and the basal tooth of the fixed finger is formed of 4 or 5, rarely 3 denticles. Since the differences are so obvious and consistent, we hereby treat them as two species. Li at al. (2007) noted that among material which they examined from Fujian, Guangdong, Hainan and Guangxi, were specimens clearly referable to both M. formosense as well as M. hainanense , and commented that the latter appears to be a good species.

This species is commercially important in Guangdong Province where it is sold live together with M. nipponense at local fish markets. It is fished for home and restaurant consumption as a special dish. Local commercial fishermen call it He xia (meaning river prawn) since it is usually found in rivers.

Distribution and habitat. Southeastern China (Fujian, Guangdong Provinces and Taiwan), Japan (Ryukyu Islands and Kyushu), and Indonesia (Java). The species seems to be restricted to shallow, sandy rivers and streams in fresh to brackish waters. It seeks shelter among in aquatic vegetation or under stone.

Figures

FIGURE 3. Macrobrachium formosense. A, entire animal in lateral view, male, cl. 28.0 mm. B, scaphocerite. C, posterior portion of the telson. Scale: A = 10 mm, B = 2.5 mm, C = 2.0 mm.

FIGURE 7. A, M. heterorhynchos, preserved specimen, paratype, female (FSTC, 02–06–11–05). B, M. heterorhynchos, preserved specimen, holotype, male (FSTC, 02–06–11–01). C, M. formosense, living specimen, male. D, M. inflatum, living specimen, female. E, M. maculatum, living specimen, male.