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A new species of freshwater crab of the genus Nanhaipotamon Bott, 1968 (Crustacea, Decapoda, Brachyura, Potamidae) from Longhai, Fujian Province, China
expand article infoMao-Rong Cai, Qi-Hong Tan§, Jie-Xin Zou§
‡ Center for Disease Control and Prevention of Zhangzhou, Zhangzhou, China
§ Nanchang University, Nanchang, China
Open Access

Abstract

A new species of freshwater crab of the genus Nanhaipotamon Bott, 1968 is described from Xiaye Village, Chengxiang Town, Longhai County, Zhangzhou City, Fujian Province, China. The new species is distinguished from congeners by the combination of characters of its carapace, third maxilliped, unequal chelipeds, triangular male abdomen and unique male first gonopod. Molecular evidence derived from partial mitochondrial 16S rRNA and COI genes also support the species as new.

Keywords

freshwater crab, new species, Oriental region, taxonomy

Introduction

The genus Nanhaipotamon Bott, 1968 was originally established by Bott (1968), with several species from Taiwan, Philippines, and the Ryukyus (Japan). Dai (1997) revised the genus and described nine species from China. The latest research on Nanhaipotamon described a new species from Macau, N. macau Huang, Wong & Ahyong, 2018 (Huang et al. 2018a). Currently, Nanhaipotamon is only known from Guangdong, Fujian, Zhejiang, Taiwan, Hong Kong, and Macau (Shih et al. 2011; Huang et al. 2018a). Prior to the present study, Nanhaipotamon contained 18 species (Dai 1999; Cheng et al. 2003; Shih et al. 2005; Cheng et al. 2009; Huang et al. 2012, 2018a; Lin et al. 2012; Lin et al. 2013).

In 2019, during a survey of freshwater crab resources in Longhai, Fujian Province, the first author collected several specimens of the genus Nanhaipotamon. In August 2020, we made another collection trip to obtain additional samples. After morphological comparison, we found the Longhai specimens to be distinct from known species of Nanhaipotamon. Molecular evidence based on the 16S rRNA and COI genes also support it as new. Therefore, we herein describe a new species, Nanhaipotamon longhaiense sp. nov.

Materials and methods

Specimens were collected from Longhai, Fujian Province by Mao-Rong Cai and preserved in 95% ethanol. The holotype and allotype were deposited at the Department of Parasitology of the Medical College of Nanchang University, Jiangxi, China (NCU MCP). Other examined materials were deposited at the Center for Disease Control and Prevention of Zhangzhou City, Zhangzhou, China (ZZCDC) and the National Tropical Disease Research Center, Shanghai, China (TDRC). Carapace width and length were measured in millimeters. The abbreviations G1 and G2 refer to the first and second gonopod. The terminology used herein primarily follows that of Dai (1999) and Davie et al. (2015).

We compared the new species with type materials of other nine species of Nanhaipotamon deposited in Chinese Academy of Sciences, Beijing, China (CAS CB). Comparative materials are as follows: Nanhaipotamon guangdongense Dai, 1997: holotype, 1♂, Guangdong Province, CAS CB 05141. Nanhaipotamon hepingense Dai, 1997: holotype, 1♂, Guangdong Province, Heping County, 7 May 1965, CAS CB 05106. Nanhaipotamon hongkongense Shen, 1940: holotype, 1♂, Hongkong, Jun. 1991, CAS CB 05107. Nanhaipotamon nanriense Dai, 1997: holotype, 1♂, Fujian Province, Putian County, Nanri Island, 15 Nov. 1975, CAS CB 05103. Nanhaipotamon pinghense Dai, 1997: holotype, 1♂, Guangdong Province, Heping County, 7 May 1965, CAS CB 05132. Nanhaipotamon pingyuanense Dai, 1997: holotype, 1♂, Pingyuan County, Guangdong Province, Sep. 1983, CAS CB 05131. Nanhaipotamon wenzhouense Dai, 1997: holotype, 1♂, Wenzhou City, Zhejiang Province, 1979, CAS CB 05143. Nanhaipotamon yongchuense Dai, 1997: holotype, 1♂, Fujian Province, Yongchun County, 29 Jun. 1977, CAS CB 05104. Nanhaipotamon huaanense Dai, 1997: holotype, 1♂, Huaan County, Fujian Province, 15 Jun. 1984, CAS CB 05105.

Institutional abbreviations used in the paper are as follows: CAS CB, Chinese Academy of Sciences, Beijing, China; NCHUZOOL, Zoological Collections of the Department of Life Science, National Chung Hsing University, Taichung, Taiwan; NCU MCP, Department of Parasitology of the Medical College of Nanchang University, Jiangxi, China; SYSBM, Sun Yat-sen Museum of Biology, Sun Yat-Sen University, Guangzhou, China; ZRC, Zoological Reference Collection of Lee Kong Chian Natural History Museum (formerly Raffles Museum of Biodiversity Research), National University of Singapore, Singapore.

Approximately 50 mg of muscle tissue was excised from ambulatory legs and chelipeds. Total genomic DNA was extracted from the tissues using the DP1902 Tissue Kit (BioTeKe Inc., Beijing, China) following the manufacturer’s protocol. Then, the 16S rRNA gene was amplified using polymerase chain reaction (PCR) with the primers 1471 (5’-CCTGTTTANCAAAAACAT-3’) and 1472 (5’-AGATAGAAACCAACCTGG-3’) (Crandall and Fitzpatrick 1996). The COI gene was amplified with primers LCO1490 and HCO2198 (Folmer et al. 1994). The PCR conditions were as follows: denaturation for 50 s at 94 °C, annealing for 40 s at 52 °C and extension for 1 min at 72 °C (33 cycles), followed by a final extension for 10 min at 72 °C. The PCR products were purified and sequenced using an ABI 3730 automatic sequencer. We performed molecular analysis with the partial mitochondrial 16S rRNA and COI genes fragment. In total, 59 sequences were used to construct phylogenetic trees (Table 1). Sequences were aligned using MAFFT v. 7.215 (Katoh and Standley 2013) based on the G-INS-I method, and the conserved regions were selected with Gblocks 0.91b (Castresana 2000) using the default settings. The best-fitting model for Bayesian Inference (BI) analysis was determined by MrModeltest v. 2.3 (Nylander 2004), selected by the Akaike information criterion (AIC). The obtained model was GTR+G+I for both genes. MrBayes v. 3.2.6 (Ronquist et al. 2012) was employed to perform BI analysis, and four Monte Carlo Markov Chains of 2,000,000 generations were run with sampling every 1,000 generations. The first 500,000 generations were discarded as burn-in. The best evolutionary model for maximum likelihood (ML) analysis was HKY+I+G for 16S rRNA and GTR+G+I for COI, determined by MEGA X (Kumar et al. 2018) based on the Bayesian information criterion (BIC). An ML tree was built based on 1000 bootstrap replicates in MEGA X (Kumar et al. 2018). The pairwise distance based on the K2P (Kimura 2-Parameter) model was calculated by MEGA X (Kumar et al. 2018).

Table 1.

GenBank accession number of the species used for phylogenetic analysis.

Species Museum number Locality GenBank number Reference
Amamiku amamensis Minei, 1973 NCHUZOOL 13125 Kagoshima, Japan 16S rRNA, AB428457 Shih et al. 2009
Apotamonautes hainanensis Parisi, 1916 NCHUZOOL Hainan, China 16S rRNA, AB428459 Shih et al. 2009
Candidiopotamon rathbunae De Man, 1914 NCHUZOOL Taiwan 16S rRNA, AB208598 Shih et al. 2006
Cryptopotamon anacoluthon Kemp, 1918 NCHUZOOL 13123 Taiwan 16S rRNA, AB428455 Shih et al. 2009
Cantopotamon hengqinense Huang, Ahyong & Shih, 2017 SYSBM 1559 Guangdong, China 16S rRNA, LC342047 Huang et al. 2017a
Chinapotamon maolanense Zou, Bai & Zhou NCU MCP 196101 Guizhou, China 16S rRNA, MH183299 Zou et al. 2018
Chinapotamon glabrum Dai, Song, Li & Liang, 1980 NCHUZOOL Guangxi, China 16S rRNA, AB428451 Shih et al. 2009
Diyutamon cereum Huang, Shih & Ng, 2017 SYSBM 1555 Guizhou, China 16S rRNA, LC198519 Huang et al. 2017b
D. cereum Huang, Shih & Ng, 2017 SYSBM 1556 Guizhou, China 16S rRNA, LC198520 Huang et al. 2017b
Geothelphusa albogilva Shy, Ng & Yu, 1994 NCHUZOOL Taiwan 16S rRNA, AB127366 Shih et al. 2004
G. marginata fulva Naruse, Shokita & Shy, 2004 NCHUZOOL 13124 Okinawa, Japan 16S rRNA, AB428456 Shih et al. 2009
G. olea Shy, Ng & Yu, 1994 NCHUZOOL 13123 Taiwan 16S rRNA, AB428455 Shih et al. 2009
Hainanpotamon fuchengense Dai, 1995 NCHUZOOL 13128 Hainan, China 16S rRNA, AB428461 Shih et al. 2009
Huananpotamon angulatum Dai, Chen, Song, Fan, Lin & Zeng, 1979 NCHUZOOL Fujian, China 16S rRNA, AB428454 Shih et al. 2009
Luteomon spinapodum Huang, Shih & Ahyong, 2018 SYSBM 001609 Guangdong, China 16S rRNA, LC383796 Huang et al. 2018a
Minpotamon nasicum Dai, Chen, Song, Fan, Lin & Zeng, 1979 NCHUZOOL 13121 Fujian, China 16S rRNA, AB428450 Shih et al. 2009
Neotiwaripotamon jianfengense Dai & Naiyanetr, 1994 NCHUZOOL 13127 Hainan, China 16S rRNA, AB428460 Shih et al. 2009
Nanhaipotamon wupingense Cheng, Yang, Zhang & Li, 2003 NCHUZOOL 13125 Fujian, China 16S rRNA, AB433548 Shih et al. 2011
N. wupingense Cheng, Yang, Zhang & Li, 2003 NCHUZOOL Fujian, China 16S rRNA, AB470496 Shih et al. 2011
N. pingyuanense Dai, 1997 CAS CB 05131 Guangdong, China 16S rRNA, AB265237 Shih et al. 2007
N. huaanense Dai, 1997 CAS CB 05105 Fujian, China 16S rRNA, AB212870 Shih et al. 2005
N. pinghense Dai, 1997 CAS CB 05132 Guangdong, China 16S rRNA, AB433553 Shih et al. 2011
N. hepingense Dai, 1997 CAS CB 05106 Guangdong, China 16S rRNA, AB433552 Shih et al. 2011
N. hongkongense Shen, 1940 NCHUZOOL Hongkong 16S rRNA, AB212869 Shih et al. 2005
N. formosanum Parisi, 1916 NCHUZOOL Taiwan 16S rRNA, AB212867 Shih et al. 2005
N. yongchuense Dai, 1997 CAS CB 05104 Fujian, China 16S rRNA, AB433546 Shih et al. 2011
N. nanriense Dai, 1997 NCHUZOOL Fujian, Chian 16S rRNA, AB212868 Shih et al. 2005
N. wenzhouense Dai, 1997 NCHUZOOL 13132 Zhejiang, China 16S rRNA, AB433543 Shih et al. 2011
N. dongyinense Shih, Chen & Wang, 2005 NCHUZOOL Dongyin, Taiwan 16S rRNA, AB212863 Shih et al. 2005
Qianguimon aflagellum Dai, Song, Li & Liang, 1980 SYSBM 001404 Guangxi, China 16S rRNA, MG709239 Huang 2018.
Ryukyum yaeyamense Minei, 1973 NCHUZOOL 13126 Okinawa, Japan 16S rRNA, AB428458 Shih et al. 2009
Socotrapotamon nojidense Apel & Brandis, 2000 ZRC 2000.2232 Socota, Yemen 16S rRNA, AB428493 Shih et al. 2009
Yarepotamon gracilipa Dai, Song, Li & Liang, 1980 ZRC Guangxi, China 16S rRNA, AB428452 Shih et al. 2009
N. longhaiense sp. nov. NCU MCP 417701 Fujian, China 16S rRNA, MT809486 This study
N. longhaiense sp. nov. NCU MCP 417702 Fujian, China 16S rRNA, MT809487 This study
N. longhaiense sp. nov. NCU MCP 417703 Fujian, China 16S rRNA, MT809488 This study
N. longhaiense sp. nov. NCU MCP 417704 Fujian, China 16S rRNA, MT809489 This study
Huananpotamon nanchengense Dai, Zhou & Peng, 1995 NCHUZOOL Jiangxi, China COI, AB511392 Shih et al. 2011
N. huaanense Dai, 1997 CAS CB 05105 Fujian, China COI, AB433572 Shih et al. 2011
N. pingyuanense Dai, 1997 CAS CB 05131 Guangdong, China COI, AB265249 Shih et al. 2011
N. wupingense Cheng, Yang, Zhang & Li, 2003 NCHUZOOL 13125 Fujian, China COI, AB433569 Shih et al. 2011
N. hongkongense Shen, 1940 NCHUZOOL Hongkong COI, AB433574 Shih et al. 2011
N. yongchuense Dai, 1997 CAS CB 05104 Fujian, China COI, AB433567 Shih et al. 2011
N. nanriense Dai, 1997 NCHUZOOL Fujian, Chian COI, AB433565 Shih et al. 2011
N. wenzhouense Dai, 1997 NCHUZOOL 13132 Zhejiang, China COI, AB433564 Shih et al. 2011
N. dongyinense Shih, Chen & Wang, 2005 NCHUZOOL Dongyin, Taiwan COI, AB433562 Shih et al. 2011
N. formosanum Parisi, 1916 NCHUZOOL Taiwan COI, AB433557 Shih et al. 2011
N. guangdongense Dai, 1997 Guangdong, China COI, MK226145 Huang et al. 2018a
N. macau Huang, Wong & Ahyong, 2018 Macau COI, MK226142 Huang et al. 2018a
N. longhaiense sp. nov. NCU MCP 417701 Fujian, China COI, MW703830 This study
N. longhaiense sp. nov. NCU MCP 417702 Fujian, China COI, MW729699 This study
N. longhaiense sp. nov. NCU MCP 417703 Fujian, China COI, MW729700 This study
N. longhaiense sp. nov. NCU MCP 417704 Fujian, China COI, MW729701 This study
N. longhaiense sp. nov. NCU MCP 417705 Fujian, China COI, MW729702 This study
N. longhaiense sp. nov. NCU MCP 417706 Fujian, China COI, MW729703 This study
N. longhaiense sp. nov. NCU MCP 417707 Fujian, China COI, MW729704 This study

Results

Systematics

Family Potamidae Ortmann, 1896

Nanhaipotamon Bott, 1968

Nanhaipotamon longhaiense sp. nov.

Figs 1, 2, 3, 4, 5A, 6, 7

Type material

Holotype : ♂ (25.2 × 21.5 mm), China, Fujian Province, Longhai County, Chengxiang Town, Xiaye Village, 24°23'02"N, 117°34'76"E, alt. 55 m, 27 Aug. 2019, Mao-Rong Cai leg, NCU MCP 417701. Paratypes: 1 ♀ (allotype) (26.5 × 22.5 mm), same data as holotype, NCU MCP 428601; 2 ♂♂ (27.1 × 22.0 mm, 29.0 × 23.3 mm), same data as for holotype, ZZCDC 613201, ZZCDC 613203.

Other specimens examined

9 ♂♂ (28.1 × 22 .6 mm, 25.3 × 20.8 mm, 22.9 × 18.9 mm, 22.8 × 18.9 mm, 22.8 × 18.9 mm, 22.3 × 18.8 mm, 22.3 × 18.8 mm, 21.4 × 17.4 mm, 21.4 × 17.1 mm), same locality data as for holotype, 10 Aug. 2020, Mao-Rong Cai and Jie-Xin Zou leg, ZZCDC 613204 to 613208, TDRC 002101to 002104; 6 ♀♀ (26.4 × 22.2 mm, 23.4 × 18.9 mm, 21.6 × 17.7 mm, 21.2 × 16.8 mm, 21.2 × 16.2 mm, 18.4 × 15.2 mm), same locality data as for preceding, ZZCDC 613213 to 613215, TDRC 002105 to 002107.

Diagnosis

Carapace subquadrate, regions indistinct, anterolateral regions slightly rugose; cervical groove shallow and wide, H-shaped groove shallow; postorbital cristae sharp, almost fused with epigastric cristae (Figs 1A, 3A). External orbital angle triangular, separated from anterolateral margin by wide, concave notch; epibranchial teeth small, granular; anterolateral margin lined with conspicuous granules (Figs 1A, 3A). Third maxilliped merus with shallow median depression, exopod flagellum slightly longer than 1/3 exopod length (Fig. 2D). Chelipeds strongly unequal; fingers with small gap when closed (Figs 1A, 3A). G1 slender, inner distal angle semicircular, inner margin of terminal segment convex, distal margin flat, outer distal angle blunt, laterally bent outwards at angle of about 60° (Figs 4A–D, 5A). Female vulvae ovate, medium-sized, wholly within sternite 6, opening directed inward (Fig. 3B).

Figure 1. 

Nanhaipotamon longhaiense sp. nov. Holotype male (25.2 × 21.5 mm) (NCU MCP 417701). A overall habitus B frontal view of cephalothorax. Scale bars: 1 cm.

Figure 2. 

Nanhaipotamon longhaiense sp. nov. holotype male (25.2 × 21.5 mm) (NCU MCP 417701) A ventral view of anterior thoracic sternum, telson, and male pleonal somites 4–6 B ventral view of sterno-pleonal cavity with G1 in situ C the fourth ambulatory leg D left third maxilliped. Scale bars: 5 mm.

Description

Carapace subquadrate, broader than long; dorsal surface smooth, distinctly convex longitudinally, with tiny pits; anterolateral region rugose. Branchial regions swollen (Figs 1A, 3A). Cervical groove shallow and wide; H-shaped groove between gastric and cardiac regions shallow (Figs 1A, 3A). Epigastric cristae conspicuous, separated by narrow gap; postorbital cristae sharp, almost fused with epigastric cristae (Figs 1A, 3A). Front distinctly deflexed, margin ridged in dorsal view. External orbital angle triangular, separated from anterolateral margin by wide, concave notch. Epibranchial tooth small, granular. Anterolateral margin distinctly cristate, lined with approximately 20 granules (Figs 1A, 3A). Posterolateral surface smooth, with inconspicuous oblique striae, converging towards posterior carapace margin (Figs 1A, 3A). Orbits large; supraorbital, infraorbital margins cristate. Sub-orbital regions covered with granules (Fig. 1B); pterygostomial regions covered with large rounded granules; sub-hepatic regions covered with striae (Fig. 1B). Posterior margin of epistome with median triangle, lateral margin sinuous (Fig. 1B).

Figure 3. 

Nanhaipotamon longhaiense sp. nov. Paratype female (26.5 × 22.5 mm) (NCU MCP 428601). A overall habitus B female vulvae C female holding eggs. Scale bars: 1 cm.

Third maxilliped merus about 1.2 times as broad as long, trapezoidal, with median depression; ischium about 1.3 times as long as broad, rectangular, with distinct median sulcus; exopod reaching approximately 1/4 of merus length, exopod flagellum slightly longer than 1/3 exopod length (Fig. 2D).

Chelipeds strongly unequal. Merus cross-section trigonal, inner-lower margin crenulated. Carpus surface weakly wrinkled, with longitudinal depression and sharp spine at inner-distal angle with spinule at base. Palm of larger chela about 1.3 times as long as high. Movable finger (dactylus) slightly shorter than the immovable finger (pollex). Inner margin of fingers with rounded, blunt teeth; fingers forming small gap when closed (Figs 1A, 3A).

Ambulatory legs slender, second leg longest, merus 0.5–0.6 times as long as carapace length; last leg with propodus 2.1 times as long as broad, slightly shorter than dactylus. Dactylus gently curved, with sharp spines on the surface (Figs 2C, 3A).

Male thoracic sternum smooth, pitted (Fig. 2A). Sternites 1, 2 completely fused to form triangular structure; sternites 2,3 separated by visible suture; sternites 3, 4 fused without obvious suture (Fig. 2A). Male sterno-pleonal cavity relatively deep, exceeding imaginary line connecting posterior edges of cheliped coxae (Fig. 2B). Median longitudinal suture of sternites 7, 8 deep and long. Tubercle of abdominal lock positioned at mid-length of sternite 5 (Fig. 2B). Female vulvae ovate, medium-sized, wholly within sternite 6, opening directed inward (Fig. 3B).

Male abdomen triangular; somites 4–6 gradually narrowed longitudinally, lateral margins slightly convex; somite 6 about 2.2 times as wide as long; telson about 1.4 times as wide as long (Fig. 2A).

G1 slender, tip of terminal segment reaches beyond pleonal locking tubercle (Fig. 2B), subterminal segment about 2.4 times as long as terminal segment (Fig. 4A). Inner distal angle semicircular, inner margin of terminal segment convex, distal margin flat, outer distal angle blunt, bent outwards at angle of about 60° (Figs 4A–D, 5A). G2 subterminal segment about 1.9 times length of distal segment (Fig. 4E).

Figure 4. 

Gonopods of holotype A ventral view of left G1 B ventral view of terminal segment of left G1 C dorsal view of left G1 D dorsal view of terminal segment of left G1 E ventral view of left G2. Scale bars: 1 mm.

Etymology

The new species is named after the county where is located, Longhai County, Zhangzhou City, Fujian Province, China.

Figure 5. 

G1s of six species of Nanhaipotamon. A N. longhaiense sp. nov., NCU MCP 417701 B N. guangdongense, Dai, 1997, CB 05141 C N. hepingense, Dai, 1997, CB 05106 D N. yongchuense, Dai, 1997, CB 05104 E N. nanriense, Dai, 1997, CB 05103 F N. huaanense, Dai, 1997, CB 05105.

Distribution

Longhai County, Zhangzhou City, Fujian Province, China.

Ecology

The new species occurs in the wetlands of low-elevation hills and mountains, amongst dense vegetation where there is little to no water flow year-round (Fig. 7B). During the day, the crabs usually hide in mud burrows close to the water source (Fig. 7A) or hide under rocks under water. We observed a berried female in August, suggesting the time around this month to be a part of the breeding season (Fig. 3C).

Remarks

With a convex carapace dorsal surface, unequal chelipeds and triangular male abdomen, Nanhaipotamon longhaiense sp. nov. fits the diagnosis of Nanhaipotamon. Like some species within this genus, N. longhaiense sp. nov. shows intraspecific variation in G1 morphology, the distal margin of the G1 terminal segment is flat to oblique (Fig. 6A–C). In the holotype, the distal margin is flat (Fig. 6A), whereas in some adult specimens, the distal margin is oblique (Fig. 6B, C), and the inner margin of the G1 terminal segment is slightly convex to distinctly convex (Fig. 6A–C).

Figure 6. 

G1s of N. longhaiense sp. nov. A holotype, NCU MCP 417701 B paratype, ZZCDC 613201 C paratype, ZZCDC 613203.

We make comparisons between the new species and seven species of Nanhaipotamon, among which N. wuping and N. macau are morphologically similar to this new species, N. yongchuense, N. huaanense and N. nanriense are geographically close (Dai 1999), and N. guangdongense and N. hepingense are from Guangdong near Fujian (Dai 1999). Nanhaipotamon longhaiense sp. nov. can be differentiated from its congeners by its unique G1 (Fig. 5A). Compared to N. longhaiense sp. nov., which has a semicircular G1 terminal segment inner distal angle, N. guangdongense, N. hepingense, N. yongchuense, N. nanriense, and N. huaanense differ in having instead a bluntly triangular G1 terminal segment inner distal angle (Fig. 5B–F). The G1 terminal segment inner distal angle is also semicircular in both N. wupingense and N. macau (Huang et al. 2018a); however, the terminal segments in these two species are proportionately larger. In N. macau, the G1 terminal segment distal margin is sinuous to V-shaped (cf. Huang et al. 2018a: fig. 5D, E). In N. wupingense, the G1 terminal segment distal margin is sinuous to an inverte V-shaped (cf. Cheng et al. 2003: fig. 7; Huang et al. 2018a: fig. 6D). In N. longhaiense sp. nov., however, the G1 terminal segment distal margin is flat to oblique (Fig. 6A–C). The detailed differences between the new species and congeners are presented in Table 2.

Table 2.

Morphological difference among eight species of Nanhaipotamon.

Species/character Ratio of flagellum length to exopod length G1 in situ Inner margin of G1 terminal segment Inner distal angle of G1 terminal segment Outer distal angle of G1 terminal segment
longhaiense sp. nov. 0.4 (Fig. 2D) Exceeding pleonal locking tubercle (Fig. 2B) Convex (Fig. 5A) Semicircular (Fig. 5A) Relatively stout; bent outwards at angle of about 60° (Fig. 5A)
N. nanriense (cf. Dai 1999: fig. 53) 0.4 Exceeding pleonal locking tubercle Gently convex (Fig. 5E) Blunt; triangular (Fig. 5E) Relatively stout; bent outwards at angle of about 45° (Fig. 5E)
N. yongchuense (cf. Dai 1999: fig. 54) 0.1 Exceeding pleonal locking tubercle Gently convex (Fig. 5D) Blunt; triangular (Fig. 5D) Relatively stout; bent outwards at angle of about 45° (Fig. 5D)
N. huaanense (cf. Dai 1999: fig. 55) 0.1 Reaching pleonal locking tubercle Gently convex Blunt; triangular Relatively slender; bent outwards at angle of about 60°
N. wupingense 0.1 (cf. Cheng et al. 2003: fig. 5) Exceeding pleonal locking tubercle (cf. Cheng et al. 2003: fig. 3) Gently convex (cf. Cheng et al. 2003: fig. 7) Distinctly expanded; semicircular (cf. Cheng et al. 2003: fig. 7) Relatively stout; bent outwards >60° (cf. Cheng et al. 2003: fig. 7)
N. macau 0.2 (cf. Huang et al. 2018a: fig. 5A) Exceeding pleonal locking tubercle (cf. Huang et al. 2018a: fig. 3D) Gently convex (cf. Huang et al. 2018a: fig. 5D, E) Distinctly expanded; semicircular (cf. Huang et al. 2018a: fig. 5D, E) Relatively stout; bent outwards at angle of about 90° (cf. Huang et al. 2018a: fig. 5D, E)
N. hepingense (cf. Dai 1999: fig. 59) 0.5 Exceeding suture 4/5 Gently convex (Fig. 5C) Blunt; triangular (Fig. 5C) Relatively stout; bent outwards >60° (Fig. 5C)
N. guangdongense (cf. Dai 1999: fig. 60) 0.5 Not reaching pleonal locking tubercle Distinctly convex (Fig. 5B) Triangular (Fig. 5B) Relatively stout; bent outwards >60° (Fig. 5B)
Figure 7. 

Habitat environment. A burrow inhabited by the new species (indicated by circle) B habitat environment.

Phylogenetic analyses

In this study, we obtained the partial mitochondrial 16S rRNA and COI genes from specimens of Nanhaipotamon collected from Xiaye Village, Chengxiang Town, Longhai County, Fujian Province, China. A total of 37 546 bp 16S rRNA gene sequences and 22 658 bp COI gene sequences were used to construct the BI and ML trees. The topological structures of the 16S rRNA and COI trees are similar. Both trees show that N. longhaiense sp. nov. and 11 other species of Nanhaipotamon are clustered into one clade (Figs 8, 9). In the 16S rRNA tree, four sequences of N. longhaiense sp. nov. form a small branch within Nanhaipotamon, while in the COI tree, the N. longhaiense sp. nov. clade and N. wupingense are sister to each other, indicating a close phylogenetic relationship between N. longhaiense sp. nov. and N. wupingense. The pairwise distances between the 12 species of Nanhaipotamon were calculated based on the COI gene. The result shows that the pairwise genetic distances between Nanhaipotamon range from 0.0239 to 0.1552 (Table 3), while distances between N. longhaiense sp. nov. and its congeners are from 0.0880 to 0.1423. Therefore, the genetic distance is large enough to support N. longhaiense sp. nov. as new. Both the phylogenetic position and genetic divergences provide evidence supporting the recognition of N. longhaiense sp. nov. as a new species.

Table 3.

Pairwise genetic distances between 12 species of Nanhaipotamon.

Species 1 2 3 4 5 6 7 8 9 10 11 12
N. formosanum
N. dongyinense 0.0269
N. wenzhouense 0.0319 0.0124
N. nanriense 0.0303 0.0255 0.0306
N. yongchuense 0.0458 0.0408 0.0425 0.0305
N. hongkongense 0.1088 0.1009 0.1031 0.0928 0.0991
N. pingyuanense 0.1552 0.1272 0.1340 0.1437 0.1390 0.1444
N. huaanense 0.1503 0.1227 0.1317 0.1437 0.1366 0.1444 0.0239
N. guangdongense 0.1243 0.1140 0.1207 0.1098 0.1302 0.0985 0.1373 0.1420
N. macau 0.1306 0.1246 0.1275 0.1159 0.1342 0.1066 0.1437 0.1461 0.0409
N. wupingense 0.1116 0.0975 0.1058 0.1039 0.1141 0.1018 0.1529 0.1529 0.1366 0.1534
N. longhaiense sp. nov. 0.0976 0.0880 0.0920 0.0922 0.0902 0.1031 0.1423 0.1329 0.1184 0.1252 0.1033
Figure 8. 

Phylogenetic tree based on 16S rRNA. Topologies and branch lengths were obtained from BI analysis. Support values represented at the nodes were from BI and ML.

Figure 9. 

Phylogenetic tree based on COI. Topologies and branch lengths were obtained from BI analysis. Support values represented at the nodes were from BI and ML.

Discussion

Nanhaipotamon is endemic to China and mainly distributed in the low-elevation coastal areas or islands in southeastern China. Due to the isolating effect of mountain ranges, Nanhaipotamon is restricted to an area east of the Wuyishan Range and south of the Nanling Range (Shih et al. 2011). With 18 species, including N. longhaiense sp. nov., species diversity in Nanhaipotamon is the highest among sympatric genera (Longpotamon, Somanniathelphusa, Huananpotamon, Bottapotamon, Minpotamon, Heterochelamon, Cantopotamon, Cryptopotamon, Eurusamon, Yarepotamon, Yuebeipotamon) except Geothelphusa. Huananpotamon is followed by Nanhaipotamon, with 15 species distributed on both sides of the Wuyishan Range (Fujian and Jiangxi Provinces) (Shih et al. 2011; Chu et al. 2018). While all the other sympatric genera consist of fewer than 10 species. Therefore, Nanhaipotamon has important value as part of the regional biodiversity.

In the morphological classification of freshwater crabs, the G1 character provide important morphological identification features (Dai 1999). Intraspecific variation in G1 morphology has been reported in some species of Nanhaipotamon, such as N. guangdongense from different localities (Huang et al. 2012; Huang et al. 2018a). In N. longhaiense sp. nov., intraspecific variation of G1 morphology was also found. Several questions have arisen due to G1 intraspecific variation: Dai (1997) described N. hepingense and N. pinghense, both from Heping County, Guangdong Province. Shih et al. (2011) provided molecular evidence that they are synonymous and many scholars agree with this (Huang et al. 2012; Chu et al. 2018). Huang et al. (2012) described N. zhuhaiense in Zhuhai, Guangdong Province, where N. guangdongense is also found. Later, Huang et al. (2018a) indicated that N. zhuhaiense and N. guangdongense are probably conspecific, but they did not have sufficient material on which to take taxonomic action. These problems were caused by intraspecific variation, which makes it difficult to classify species based on morphology alone. Therefore, when describing a new species of this genus, it is recommended that morphological classification be combined with molecular analysis. There are likely other problems with some species in this genus, and therefore a revision is necessary.

Conclusion

In this article, we report a new species of Nanhaipotamon collected from Xiaye Village, Chengxiang Town, Longhai County, Fujian Province, China. Nanhaipotamon longhaiense sp. nov. can be distinguished from congeners by the combination of carapace, third maxilliped, and male first gonopod characters. Molecular evidence based on the mitochondrial 16S rRNA and COI genes also support it as a new species of the genus Nanhaipotamon.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (no. 32060306 and 21866020), the National Parasitic Resources Center (NPRC-2019-194-30), the Zhangzhou National Science Foundation of Fujian (no. ZZ2017J09), the Zhangzhou Key Project of Science and Technology Plan (no. ZZ2017ZD05), the Nanchang University College Students’ Innovation and Entrepreneurship Training Program (no. 2020CX298), and Nanchang University’s Scientific Research Training Program (no. 15334). We thank Jun Luo from Zhangzhou center for disease control and prevention for assisting in specimen collection. We thank Song-Bo Wang from Nanchang University for giving advice in writing and taking the photographs. We thank Dr Chao Huang (Australian Museum) for helping with our written language. Finally, we give a special thanks to subject editor and reviewers for greatly improving our manuscript.

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