Nanhaipotamon dongyinense, Shih & Chen & Wang, 2005

Shih, Hsi-Te, Chen, Guo-Xiao & Wang, Li-Min, 2005, A new species of freshwater crab (Decapoda: Brachyura: Potamidae) from Dongyin Island, Matsu, Taiwan, defined by morphological and molecular characters, with notes on its biogeography, Journal of Natural History 39 (31), pp. 2901-2911 : 2904-2909

publication ID	https://doi.org/ 10.1080/00222930500214010
persistent identifier	https://treatment.plazi.org/id/03948796-FFCB-7D49-FE73-FCE9367154CD
treatment provided by	Felipe
scientific name	Nanhaipotamon dongyinense
status	sp. nov.

Treatment

Nanhaipotamon dongyinense View in CoL sp. nov.

( Figures 2A–H View Figure 2 , 3A–D View Figure 3 )

Holotype: one male (31.3× 25.8 mm) ( NMNS 4557-001 View Materials ), Yansiouwo, Dongyin (26 ° 219910N, 120 ° 289960E), Matsu, Taiwan, coll. L.-M. Wang, June 2004 . Paratypes: one female (allotype) (26.5× 22.2 mm) ( NMNS 4557-002 View Materials ), same data as holotype ; five males ( CW 29.47–36.28 mm) ( NMNS 4557-003 View Materials to 4557-007 View Materials ) , five females ( CW 29.64– 34.76 mm) ( NMNS 4557-008 View Materials to 4557-012 View Materials ), same locality as holotype, coll. L.-M. Wang, H.- T. Shih , H.- T. Hung, and N.-H. Jang-Liaw, 15 July 2004 ; one male ( CW 22.4 mm) ( IZCAS 0401 View Materials ), same data as holotype ; one male ( CW 28.27 mm) , one female ( CW 27.84 mm) ( IZCAS 0402 View Materials ), same locality as holotype, coll. L.-M. Wang, H.- T. Shih , H.- T. Hung, and N.-H. Jang-Liaw, 15 July 2004 ; two males ( CW 32.05 , 32.51 mm) , two females ( CW 26.62 , 29.03 mm) ( ZRC 2004.0694 View Materials ), same locality as holotype, coll. L.-M. Wang, H.- T. Shih, H.- T. Hung , and N.-H. Jang-Liaw, 15 July 2004 . Others : five males ( CW 19.15–29.56 mm) , two females ( CW 26.40–26.91 mm) ( NMNS 4557-013 View Materials ), same locality as holotype, coll. L.-M. Wang, H.- T. Shih , H.- T. Hung, and N.-H. Jang-Liaw, 15 July 2004 .

Description. Carapace distinctly convex longitudinally, surface smooth, finely pitted. Branchial region very swollen, cervical groove wide and deep. H-shaped groove between gastric and cardiac regions deep. Postfrontal lobe prominent, with large pits. Postorbital crest sharp, connected with epibranchial tooth. Front deflexed, anterior border emarginated medially, dorsal orbital border ridged. Exorbital angle triangular, outer border arched. Epibranchial teeth squarish, antero-lateral border carinated, anterior part with indistinct granules, posterior part smooth. Third maxilliped ( Figure 2A View Figure 2 ) with merus about 1.2 times as broad as long, with ischium about 1.5 times as long as broad, exopod reaching to proximal third of merus, with a short flagellum.

Chelipeds strongly unequal, carpus with longitudinal depression on dorsal surface, with rugae on inner border, inner-distal angle with acute spine and spinule; larger manus about 1.3 times as long as high, slightly shorter than movable finger, with large gape when closed. Ambulatory legs slender, last leg with propodus about 2.4 times as long as broad, shorter than dactylus.

Male abdomen ( Figure 2B View Figure 2 ) triangular, sixth segment about 2.3 times as broad as long, telson about 1.2 times as broad as long. Median longitudinal groove of thoracic sternum deep, interruption between sutures of sternites narrow, median longitudinal suture of sternites 7 and 8 moderately long.

Male G1 (first pleopod) ( Figure 2D, E View Figure 2 ) reaching beyond tubercle of abdominal lock ( Figure 2C View Figure 2 ), subterminal segment about 2.7 times as long as terminal segment, terminal segment resembling an upside down boot in shape, its median line about 2.3 times as broad as long. Inner distal angle blunt triangular, distal margin arched inwards, outer distal angle produced, horn-like, distal end with pore. Male G2 (second pleopod) ( Figure 2F View Figure 2 ) with subdistal segment about 1.9 times as long as distal segment.

Female abdomen ( Figure 2G View Figure 2 ) oval, sixth segment about 3.1 times as broad as long, telson about 2.1 times as broad as long. Gonopore ( Figure 2H View Figure 2 ) with upper part widening gradually, like watermelon seed, opening inwards and downwards.

Carapace length of holotype male 25.8 mm, breadth 31.3 mm; of allotype female, length 22.2 mm, breadth 26.5 mm.

Etymology. Nanhaipotamon dongyinense is named for the type locality, Dongyin Island, Matsu.

Coloration ( Figure 3A–D View Figure 3 ). Carapace is greenish gray and ambulatory legs are yellowish green. Female individuals tend to be more yellowish.

Habitat. The specimens were found in the irrigation ditches next to vegetable gardens ( Figure 3E View Figure 3 ). The water source is from the springs of this small island. No freshwater shrimps or freshwater snails were found. Brooding females could be found from April to June. A mating pair was found near the entrance within the burrow during July. Sometimes a wall of mud (hood or chimney) around the entrance can be observed ( Figure 3F View Figure 3 ), especially in habitats far from surface water.

Distribution. The largest population is located in Yansiouwo, eastern part of Dongyin. Some burrows could also be found in Bei-ao, north of Yansiouwo. In the western part of Dongyin (Siyin), local people stated that some crabs were seen in Hou-ao and Rendingshengtian ( Figure 1 View Figure 1 ), but none were obtained in the present study.

Remarks. Nanhaipotamon dongyinense sp. nov. can be distinguished from the other congeners— N. nanriense Dai, 1997 , N. formosanum ( Parisi, 1916) , and N. huaanense Dai, 1997 . The morphological differences among them are shown in Table II.

DNA analysis

A 548 base pair segment (excluding the primer regions) of the 16S mtDNA gene from five species of Nanhaipotamon was amplified and aligned. Out of those, 45 positions were variable and 10 were parsimony informative. Among the total number of sequences, eight different haplotypes were found ( Table I). The segment of 16S sequences is AT-rich (72%) (T: 36.4%, A: 35.6%, G: 17.8%, C: 10.3%).

Among the populations of Nanhaipotamon formosanum , the difference in nucleotide number is within 2 bp. N. dongyinense differs from N. formosanum by 6–8 bp, and differs from N. nanriense by 10 bp. There is a 5–6 bp difference between N. nanriense and N. formosanum (Table III). The phylogenetic tree constructed by the Kimura two-parameter model of the NJ analysis, with the bootstrap values larger than 50% from MP analysis, is shown in Figure 4 View Figure 4 . Both NJ and MP methods support that N. formosanum from the populations of Taiwan form one clade, with N. nanriense forming the sister groups of N. formosanum .

areas.

nov. (Dongyin, Matsu), N. nanriense (Nanri, Fujian), N. hongkongense ( Hong Kong) and N. aculatum ( Hong Kong) ( Dai 1999; this study). In comparison, there are two species of the genus Geothelphusa Stimpson, 1858 on Lanyu and Lyudao, two offshore islands east of Taiwan ( Shy et al. 1994). Because deep oceanic trenches separate these two islands and Taiwan, a land bridge theory cannot explain their distribution. Considering the genetic similarities between G. tawu Shy, Ng and Yu, 1994 (from main island of Taiwan), G. lanyu Shy, Ng and Yu, 1994 (Lanyu) and G. lutao Shy, Ng and Yu, 1994 (Lyudao) , the three species are very close, and are considered as the same species. Their presence on the two islands may be explained by rafting, or dispersal by birds, or even humans from Taiwan Island ( Shih et al. 2004). The colonization of N. dongyinense sp. nov. is believed to be different from that of Geothelphusa spp. in Lanyu and Lyudao. Although Dongyin is more than 50 km from mainland Fujian, it nevertheless sits on the continental shelf. During periods of glaciation and low sea levels, Taiwan was probably connected to mainland China ( Boggs et al. 1979). The isolation and evolution of N. dongyinense sp. nov. in Dongyin is thus believed to be a recent vicariant event.

In addition to the morphological difference (Table II), N. dongyinense sp. nov. also differs from congeners at the molecular level. Based on the tree topology ( Figure 4 View Figure 4 ), N. dongyinense sp. nov. forms a distinct clade with N. formosanum and N. nanriense . From Table III, there is at least 6 bp difference between N. dongyinense and N. formosanum . In comparison, Shih et al. (2004) have reported that there is no more than 5 bp nucleotide difference within the Geothelphusa tawu clade in southern Taiwan.

It is believed that N. dongyinense was originally distributed throughout Dongyin Island, but anthropogenic factors have affected several populations. The main reasons include the development of military building operations, overuse of pesticides and herbicides, cemented trenches, and pollution from a winery. Without appropriate conservation, the endemic species may well be exterminated in the future.