Macrobrachium lingyunense, Clarke, 2006

Clarke, Jingchun Li Yixiong Cai Arthur, 2006, A New Species Of Troglobitic Freshwater Prawn Of The Genus Macrobrachium From Southern China (Crustacea: Decapoda: Palaemonidae), Raffles Bulletin of Zoology 54 (2), pp. 277-282 : 277-281

Macrobrachium lingyunense , new species

( Figs. 1-3 )

Material examined. – Holotype: Male , cl 13.6 mm, (IZCAS-DE-1) Shadong ( Sand Cave ), Guancang Village , Sicheng Town, Lingyun County, Guangxi Province, southern China (106 ° 23' - 106 ° 55’33"E 24 ° 05' - 24 ° 37'N), coll. Chunguang Zhang, 26 Nov.2001 . Paratypes: 2 males, cl 11.4-12.1 mm (IZCAS-DE-3, 4), 1 female, cl 17.2 (IZCAS-DE-2), one juvenile, cl 14.3 mm (IZCAS-DE-4), data same as holotype ; one female, cl 15.1 mm ( ZRC), Shadong ( Sand Cave ), north of Lingyun Town, Lingyun County, Guangxi Province, southern China (106 ° 36'33.12947"E 24 ° 25'21.42550"N), coll. Arthur Clarke, 11 Oct.2000 . 1 male, cl 12.8 mm; 1 female, cl 8.5 mm ( ZRC 2005.0138 ), Shadong ( Sand Cave ), north of Lingyun Town, Lingyun County, Guangxi Province, southern China (106 ° 36'33.12947"E 24 ° 25'21.42550"N), coll. Arthur Clarke, 11 Oct.2000 ; 1 male, cl 11.5 mm, TM, Shadong ( Sand Cave ), north of Lingyun Town, Lingyun County, Guangxi Province, southern China (106 ° 36'33.12947"E 24 ° 25'21.42550"N), coll. Arthur Clarke, 11 Oct.2000 .

Description. – Carapace smooth. Rostrum ( Fig. 1A ) straight, reaching distal end of scaphocerite, rostral formula: 2-4+5- 7/3-4. Teeth more widely spaced on above orbit region than on anterior and postorbital regions. Antennular peduncle about 0.4 times as long as carapace. Antennal spine sharp, situated at lower orbital angle, not reaching anterior margin. Hepatic spine smaller than antennal spine, lying behind and slightly below latter. Carapace smooth.

Fourth thoracic sternite without median process. Abdomen smooth, glabrous, first to third pleurites broadly rounded, fourth and fifth pleurites feebly produced posteriorly, fourth pleurite sub-triangular, fifth pleurite sub-rectangular, sixth abdominal somite slightly longer than fifth, with posteroventral angle feebly produced, subacute. Telson ( Fig. 2G ) long, slender, 3.8 times as long as wide, 1.8 times as long as sixth abdominal segment, with a shallow median groove on dorsal surface, with 2 pairs of dorsal spines, ending in a small acute median point, lateral spines slightly larger than dorsal spines, sublateral pair of spines well developed, long and stout, more than 3 times as long as lateral pair, with 2-4 pairs of intermediate plumose setae. First 2 abdominal sternites ( Fig. 1H ) with transverse ridge and a median tooth each, second abdominal sternite very prominent, more developed than first abdominal sternite. Preanal region unarmed, smooth.

Eyes strongly reduced, small, rounded, lacking faceted cornea, no pigment visible, anterior end only reaching middle of basal segment of antennular peduncle. Stylocerite pointed, reaching 0.7 basal segment. Antenna with stout basicerite and strong distoventral tooth. Carpocerite reaching to about 0.3 times of scaphocerite length. Scaphocerite ( Fig. 2F ), about 2.4 times as long as wide, with straight outer margin.

Epistome ( Fig. 1B ) bilobed by a depression. Mouth parts typical of genus. Mandible ( Fig. 1C ) with 3-segmented slender palp; incisor process robust; maxillular palp bilobed ( Fig. 1D ), upper lobe slender, pointed, lower lobe stout; maxilla ( Fig. 1E ) with simple palp, basal endite deeply bilobed, scaphognathite normal; first maxilliped ( Fig. 1F ) with simple palp, basal and coxal endites distinct, flagellum of exopod with numerous plumose setae distally, epipod deeply bilobed; second maxilliped with normal endopod ( Fig. 1G ), flagellum with numerous plumose setae distally, epipod simple, with well developed podobranch; third maxilliped ( Fig. 2A ) with robust endopod, exopod short, with numerous plumose setae distally.

First pereiopods ( Fig. 2B ) very slender, reaching beyond scaphocerite by entire chela and 0.2 carpus length, equal in length, similar in form, carpus 1.5 times as long as chela, chela with fingers slightly longer than palm. Second pereiopods ( Fig. 2C ) not sexually dimorphic; both cylindrical, equal in length, similar in form, smooth, slightly longer than body length, reaching beyond distal end of scaphocerite by both entire carpus and chela; merus as long as carpus, both segments distinctily longer than palm but shorter than fingers; palm slightly inflated, fingers about twice as long as palm, with only 1 pair of very small teeth at base. Third pereiopods ( Fig. 1D, E ) slender, reaching beyond scaphocerite by entire dactylus and 0.25 times of propodus length, propodus 12 times as long as broad, 3.0 times as long as dactylus; dactylus 6.0 times as long as wide, terminating in a small claw. Fourth pereiopods slender, longer than third pereiopod, similar in form. Fifth pereiopods most slender, longest, reaching beyond scaphocerite by entire dactylus, slightly more than 0.5 times length of propodus.

Endopod of male first pleopod about 0.4 times as long as exopod, weakly broadened distally, slightly curved mesially. Appendix masculina of male second pleopod with numerous spiniform setae on dorsal surface. Appendix interna of male second pleopod slender, reaching to 0.6 length of appendix masculina.

Uropodal diaeresis ( Fig. 2H ) with a very small spine, distinctly shorter than outer angle.

Habitat. – Some paratypes of the present new species were collected from a one-meter deep water pool at about 1.5 km from the only known entrance of the sand cave. It was in total darkness and situated in an upper level relict karst passage where the dominant hydrology is percolation seepage ( Clarke, 2002b).

Colouration. – All appendages generally transparent to translucent; carapace and abdomens whitish to yellowish ( Fig. 3 ).

Etymology. – The new species is named after the type locality: Lingyun County, NW Guangxi Province, China.

Remarks. – Macrobrachium lingyunense , new species, is the first troglobitic Macrobrachium species found in China. Compared to epigean species, it is morphologically closest to M. guangxiense Liang and Yan, 1981 , a species known only from Guangxi Province, especially when taking the slenderness of the second pereiopods into consideration. Macrobrachium lingyunense , however, differs remarkedly from M. guangxiense by the highly reduced eyes and the relatively lower rostral base with smaller number of dorsal rostral teeth (7-10 vs. 12-16). The general appearance and the ratios of various segments of the second pereiopods of this new species are also similar to those of M. inflatum Liang & Yan, 1985 . However, M. lingyunense can be easily distinguished from M. inflatum by the reduced eyes and proportionately shorter and less curved rostrum (vs. relatively longer and distinctly curved rostrum). Macrobrachium inflatum was originally described from Jiangsu Province, eastern China (Liang & Yan, 1985) but has subsequently been found in Yunnan (Cai & Dai, 1999). Macrobrachium lingyunense also resembles sub-adult specimens of M. nipponense (De Haan, 1849) in the form of the rostrum and the second pereiopods, but can be easily separated by the degenerated eyes and the far more elongated fingers of the second pereiopods.

Holthuis (1986) listed six troglobitic Macrobrachium species i.e., M. cavernicola ( Kemp, 1924) , M. villalobosi Hobbs, 1973 , M. lucifugum Holthuis, 1974 , M. acherontium Holthuis, 1977 , M. microps Holthuis, 1978 and M. poeti Holthuis, 1984 . Chong (1989) described M. gua from Sabah, Malaysia, Hobbs & Hobbs (1995) described M. catonium from Middle America, and Komai & Fujita (2005) recently reported another new troglobitic species, M. miyakoense from the Ryukyu Islands, Japan, bringing to a total of nine troglobitic species. Of these nine mentioned species, only M. villalobosi from Oaxaca, Mexico, could be confused morphologically with M. lingyunense . In the Mexican species, the eyes have no pigment and lack faceted cornea; the chelae of the slender second pereiopods are subequal in size, lacking teeth, spines and conspicuous mats of setae on finger or palm. However, it can be distinguished by its proportionately much longer carpus of the second pereiopods, which is even longer than the chela (vs. shorter in M. lingyunense ).

Of the remaining cave species, M. lucifugum and M. gua actually do not possess specific troglobitic characters, though the former has been found in caves of several islands in the West Indies, and the latter has only been found from a cave in Sabah, East Malaysia, Borneo. Macrobrachium cavernicola , M. microps , M. poeti , M. acherontium , and M. miyakoense can easily be separated from M. lingyunense by their less prominently reduced eyes. In particular, the American M. acherontium is morphologically close to M. lingyunense in the form of the various legs and ratios of the various joints of the second pereiopods, but in addition to its larger eyes, it also has a proportionately shorter and higher rostrum. Macrobrachium cavernicola from Siju Cave in Assam, India, was the first troglobitic Macrobrachium species to be described and it differs from all the other congeners by the peculiar two-segmented mandible palp.

Macrobrachium microps was originally described by Holthuis (1978) from Danmin Cave, New Ireland ( Papua New Guinea) on the basis of only one adult male, collected from a fast flowing subterranean river, at altitude of 600-700 meters. Macrobrachium microps can be easily separated from M. lingyunense by the stout and spiny second pereiopods (smooth in M. lingyunense ). Bruce & Iliffe (1993) reported a second occurrence of M. microps from an anchialine lava tube in Samoa. Short & Marquet (1998: 408) reported two other “immature” male specimens from a cave in the Lifou Island, New Caledonia. In a subsequent paper, Short & Meek (2000) reported one adult female and one undeveloped male of M. microps from Daniel Roux Cave, Christmas Island, in the Indian Ocean.

Holthuis (1984) described M. poeti , from a cave on the south coast of Java, Indonesia. Apart from the partially reduced eyes, M. poeti is similar to young specimens of M. pilimanus group, a group of landlocked species distributed in the Greater Sunda Islands, Peninsular Malaysia, and Indochina. Among those species, it is most similar to the Javan endemic M. leptodactylus (De Man, 1892) . Macrobrachium poeti can easily be separated from M. lingyunense by its very short carpus of the second pereiopod.

Hobbs & Hobbs (1995) described M. catonium from two caves on the Vaca Plateau, Cayo District of Belize, Middle America. It could be easily separated from M. lingyunense by its much longer carpus of second pereiopod, which is 1.2 times as long as the chela (vs. much shorter than chela).

Komai & Fujita (2005) described M. miyakoense from an anchialine cave in Miyako Island, the Ryukyu Islands, southern Japan. With regard to the chelipeds, it is superficially close to M. lingyunense . However, it can be easily separated by the better developed eyes, the larger number of dorsal rostral teeth (11-13 vs 7-9 in M. lingyunense ), the proportionately stouter telson ( Fig. 2F in Komai & Fujita, 2005 vs. Fig. 2G in this paper) and a relatively higher and more prominent preanal carina.

Figures

Fig. 1. Macrobrachium lingyunense, new species: A, cephalothorax; B, epistome; C, mandible; D, maxillula; E, maxilla; F, first maxilliped; G, second maxilliped; H, first two abdominal sterna with transverse ridge and median tooth.A, paratype, female, cl 15.1 mm (ZRC 2005.0138); B-H, paratype, male, cl 12.8 mm (ZRC 2005.0138). Scale bars: A = 2 mm; B-D, H = 0.5 mm; E-G = 1 mm.

Fig. 2. Macrobrachium lingyunense, new species:A, third maxilliped; B, first pereiopod; C, male major second pereiopod; D, third pereiopod; E, propodus and dactylus of third pereiopod; F, scaphocerite; G, telson, H, uropodal diaeresis. A, paratype, male, cl 12.8 mm (ZRC 2005.0138); B-H, paratype female, cl 15.1 mm (ZRC 2005.0138). Scale bars: A-D, F = 2 mm; E, H = 0.5 mm; G = 1 mm.

Fig. 3. Color photograph of Macrobrachium lingyunense, new species: paratype, female, cl 15.1 mm (ZRC 2005.0138).