Metaplax longipes Stimpson, 1858

Shih, Hsi-Te, Hsu, Jhih-Wei, Wong, Kingsley J. H. & Ng, Ngan Kee, 2019, Review of the mudflat varunid crab genus Metaplax (Crustacea, Brachyura, Varunidae) from East Asia and northern Vietnam, ZooKeys 877, pp. 1-29 : 1

Metaplax longipes Stimpson, 1858 Figures 2 D–F , 4 , 7 E–H

Metaplax longipes Stimpson, 1858: 97 (type locality: Hong Kong); Koelbel 1897: 711, pl. 1(5-6) (Hong Kong); Stimpson 1907: 99 (Hong Kong); Tesch 1918: 116 (key; no new specimens); Gee 1926: 164 (China: "Chin Bey"); Gordon 1931: 528 (Hong Kong; China: Amoy (= Xiamen), Fujian); Shen 1940a: 74, 95 (China: Zhejiang; Fujian); Shen 1940b: 236 (Hong Kong); Shen and Dai 1964: 133, 1 unnumbered fig. (China: Zhejiang; Fujian; Guangdong); Dai et al. 1986: 508, fig. 288 (1-2), pl. 72(3) (China: Zhejiang; Fujian; Guangdong) (part); Chen 1991: 441, fig. 416; Dai and Yang 1991: 556, fig. 288 (1-2), pl. 72(3) (China: Zhejiang; Fujian; Guangdong) (part); Davie 1992: 352 (key); Huang 1994: 598 (list; China); Wang and Liu 1996c: 227 (list); Lee 2001: 115, 3 unnumbered figs (W Taiwan); Ng et al. 2001: 54 (list; Taiwan); Davie and Nguyen 2003: 384 (no specimen examined); Wang 2003: 111, 1 unnumbered fig. (Taiwan: Kinmen); Liu and He 2007: 167: 1 unnumbered fig. (China: Yangtze R. estuary); So and Lui 2007: 36, 3 unnumbered figs (Hong Kong); Huang 2008: 668 (list; China); Ng et al. 2008: 226 (list); Yang et al. 2008: 803 (list; East and South China seas); Ng et al. 2017: 110 (list; Taiwan).

Metaplax takahasii Sakai, 1939: 698, text-fig. 127 (type locality: Tansui (= Danshuei), Taiwan); Sakai 1940: 58 (list; Japan; Taiwan); Lin 1949: 31 (list; Taiwan); Fukui et al. 1989: 230, fig. 24 (Taiwan: New Taipei City); Dai and Yang 1991: 556, fig. 288 (3-4), pl. 72(4) (China: Fujian; Guangdong); J.-T. Shih et al. 1991: 126 (Taiwan: New Taipei City); Davie 1992: 352, pl. 2A (Hong Kong); Lee and Leung 1999: 69 (Hong Kong).

Metaplax takahashii : Horikawa 1940: 30 (list; Taiwan); Sakai 1976: 673, text-fig. 371 (Taiwan: Danshuei); Dai et al. 1986: 508, fig. 288 (3-4), pl. 72(4) (China: Fujian; Guangdong); Huang 1994: 598 (list; China); Kosuge et al. 1997: 182 (Vietnam: Haiphong); Muraoka 1998: 54 (Danshuei R., Taiwan); Ng et al. 2001: 46 (list; Taiwan); Kitaura et al. 2002: 684 (Vietnam: Haiphong); Davie and Nguyen 2003: 384 (no new specimens); Ng et al. 2017: 110 (list; Taiwan); Huang 2008: 668 (list; China); Ng et al. 2008: 226 (list; Taiwan).

? Metaplax longipes : Naiyanetr 2007: 112 (list: Gulf of Thailand).

Not Metaplax longipes : Davie 1992: 352 (key) (= Metaplax tredecim Tweedie, 1950).

Not Metaplax longipes : Chertoprud et al. 2012: 276, pl. 47F (Nha Phu, southeastern Vietnam) (= Metaplax tredecim Tweedie, 1950).

Materials examined.

China: 2 ♂♂ (20.7-22.7 mm) (NCHUZOOL 15443), Sheyang, Jiangsu, coll. W.-R. Lin, 24 Aug. 2015; 3 ♂♂ (11.3-22.3 mm), 1 ♀ (21.6 mm) (NCHUZOOL 15444), Mamu, Zhoushan, Zhejiang, 26 July 2018; 6 ♂♂ (15.9-26.6 mm), 3 ♀♀ (18.0-19.15 mm) (NCHUZOOL 15446), Mamu, Zhoushan, Zhejiang, Sep. 2018; 2 ♂♂ (13.9-15.6 mm), 5 ♀♀ (13.6-23.6) (NCHUZOOL 15447), Mamu, Zhoushan, Zhejiang, 26 July 2018; 1 ♀ (16.8 mm) (NCHUZOOL 15445), Buqiangwan, Zhoushan, Zhejiang, 26 July 2018; 2 ♂♂ (12.0-12.1 mm), 4 ♀♀ (9.8-18.6 mm) (NCHUZOOL 15448), Liuwudian, Xiamen, Fujian, 31 July 2018; 1 ♂ (19.2 mm) (NCHUZOOL 15449), Qinzhou, Guangxi, 10 May 2009. Hong Kong: 1 ♂ (18.3 mm) (NCHUZOOL 15451), Tung Chung, coll. K. J. H. Wong, 21 Mar. 2009; 1 ♂ (15.4 mm) (ZRC 2019.0581), 4 ♂♂ (11.2-16.7 mm) (NCHUZOOL 15450), Tung Chung, coll. K. J. H. Wong, 9 Apr. 2016; 1 ♂ (9.3 mm), 2 ♀♀ (8.6-9.8 mm) (NCHUZOOL 15452), Tung Chung, coll. K. J. H. Wong, 11 July 2015; 15 ♂♂ (6.6-12.7 mm), Tung Chung, coll. K. J. H. Wong, 17 July 2015; 4 ♂♂ (6.0-8.8 mm) (NCHUZOOL 15455), Tung Chung, coll. K. J. H. Wong, 18 July 2011; 3 ♂♂ (17.7-23.7 mm), 1 ♀ (13.3 mm), Tung Chung, coll. K. J. H. Wong, 22 Apr. 2019; 3 ♂♂ (6.8-8.6 mm), 3 ♀♀ (10.0-14.7 mm) (NCHUZOOL 15503), Tung Chung, coll. H.-T. Shih and K. J. H. Wong, 2 June 2019; 1 ♂ (17.6 mm) (NCHUZOOL 15502), Lantau Island, 2 June 2019; 2 ♂♂ (9.9-22.3 mm); 1 ♂ (24.8 mm), 1 ovig. ♀ (19.0 mm) (ZRC 2019.0542), ca. 22.495486N, 114.029947E, mudflats at mangroves, Mai Po Nature Reserve, coll. K. J. H. Wong, 24 May 2019. Macao: 1 ♀ (17.5 mm) (NCHUZOOL 15454), Coloane, coll. K. J. H. Wong, 3 July 2015. Taiwan: 1 ♀ (17.7 mm) (KPM-NH 0107076), Danshuei, New Taipei City, coll. S. Takahashi (?), 1933 (?); 1 ♀ (14.7 mm) (NTOU), Danshuei, New Taipei City, 25 May 1984; 1 ♀ (14.4 mm) (NTOU), Danshuei, New Taipei City, coll. L.-H. Hsieh, 7 May 1992; 2 ♂♂ (10.6-20.0 mm) (ASIZ), Danshuei River mangroves, New Taipei City, 17 Mar. 1986; 1 ♂ (24.1 mm) (ZRC 1999.0708), Danshuei, New Taipei City, 8 July 1999; 1 ♂ (21.8 mm) (ZRC 1999.0708), Danshuei, New Taipei City, 8 July 1999; 3 ♂♂ (6.9-17.4 mm), 2 ♀♀ (7.9-10.3 mm) (NCHUZOOL 15458), Wujiang R. estuary, Kinmen, 6 Mar. 2008; 1 ♂ (19.1 mm), 1 ♀ (16.9 mm) (NCHUZOOL 15459), Wujiang R. estuary, Kinmen, 16 Aug. 2011; 7 ♂♂ (7.4-14.6 mm), 1 ♀ (9.3 mm) (NCHUZOOL 15460), Wujiang R. estuary, Kinmen, coll. H.-T. Shih and P.-Y. Hsu, 29 June 2018; 2 ♂♂ (7.0-7.1 mm) (NCHUZOOL 15461), Cihhu, Kinmen, coll. H.-T. Shih and P.-Y. Hsu, 29 June 2018; 1 ♀ (19.9 mm) (NCHUZOOL 15462), Mashan, Kinmen, 17 Aug. 2011; 1 ♀ (21.1 mm) (NCHUZOOL 1551), 1 ♀ (5.9 mm) (NCHUZOOL 15552), 1 ♂ (20.6 mm), 1 ♀ (17.5 mm) (NCHUZOOL 15553), 1 ♀ (20.1 mm) (NCHUZOOL 15554), Lieyu, Kinmen, coll. H.-T. Shih and P.-Y. Hsu, 28 June, 2018; 1 ♂ (18.1 mm) (NCHUZOOL 15463), Cingshuei, Matsu, coll. J.-H. Li, 9 July 2005; 1 ♂ (20.0 mm) (NCHUZOOL 15464), Cingshuei, Matsu, coll. J.-H. Li, 9 July 2005.

Diagnosis.

Carapace ( Figs 2D , 4A, E, F ) subquadrate, 1.36 times broader than long (N = 98, SD = 0.05), mildly convex longitudinally and laterally, region faintly defined; front medially slightly concave; lateral margin nearly parallel, interrupted by four notches (cutting into five teeth), anterior two lateral teeth pronounced, posterior two very indistinct; posterior facet depressed, decorated by two oblique granular ridges, anterior one extended from second notch. Infraorbital ridge ( Figs 2E , 4C ) marked sexually dimorphic: males with 7-13 lobes and tubercles, medial 2 broad, decreasing in breadth laterally, innermost four or five decreasing in size, lateral ones small, isomorphic; females with 16-22 small isomorphic tubercles. Chelipeds ( Figs 2F , 4D ) symmetrical, robust, palm 2.3 times as long as broad, length of palm approximately 1.3 times length of dactyl (N = 16), merus denticulate along anterior and posterior margins; chelae surface smooth, pollex and dactylus unarmed of pronounced molars along cutting edge. Ambulatory legs slender, elongated, meri unarmed along anterior margin, proximal half of meri, and propodi of all furnished with setal mats. G1 ( Fig. 7 E–H ) elongated, relatively stout, almost straight.

Distribution.

Western Taiwan (including Matsu and Kinmen), China (Jiangsu; Zhejiang; Fujian; Guangdong; Guangxi), and northern Vietnam (Haiphong) ( Fig. 1 ). The record in the Gulf of Thailand ( Naiyanetr 2007: 112) requires further verification.

Habitat.

At Tung Chung Wetland, Hong Kong, where numerous specimens were collected, the habitat of this species is composed of muddy substrates and substantial freshwater influences. Considerable numbers flourish under fringes of mangrove stands, as well as the adjacent more open mudflats.

Remarks.

The identity of Metaplax longipes had long remained unclear since the publication of M. takahasii Sakai, 1939. The confusion between the two nominal species was mainly caused by two crucial morphological features used for species identification: the number of tubercles and lobes along the male infraorbital ridge, and the number of teeth on the lateral margin of the carapace.

Originally described from Hong Kong by Stimpson (1858, 1907), type material(s) of M. longipes was destroyed in the Great Chicago Fire in 1871 ( Evans 1967). Illustrations based on material from Hong Kong were eventually presented by Koelbel (1897: pl. 1(5-6)), and further records from Hong Kong and elsewhere in South China include those by Gee (1926), Gordon (1931), Shen (1940a, b) and Shen and Dai (1964). Morphology of the infraorbital ridge in males serves as a good taxonomic character ( Tesch 1918); delimitations provided in various work under the name M. longipes range from 7 to 10: “seven-lobed” ( Stimpson 1907), "fogak száma összesen tehát kilencz" (= total number of nine teeth; Koelbel 1897), "number of lobules or teeth … 7 –9” ( Tesch 1918, Gordon 1931), and "9 to 10 tubercles" ( Shen and Dai 1964).

Interpretations of M. longipes by Dai et al. (1986) and Dai and Yang (1991) brought much confusion. These authors illustrated two forms of infraorbital ridges based on specimens from South China (Guangdong to Zhejiang), one bearing 17 lobes and tubercles, and the other bearing nine (fig. 288(1) in Dai et al. 1986 and Dai and Yang 1991). It appeared very likely that their material was composite (also see Remarks under M. tredecim ). Anyhow, this “shift” in the number of tubercles was subsequently followed by various authors: "with 15-17 lobules and teeth" ( Davie 1992) and "about 9-17 tubercles" ( Lee and Leung 1999). Reflecting this confused situation, the dichotomous key to the Metaplax species provided by Davie (1992: 352), which differentiated " M. longipes " (15 to 17 lobules and teeth) from " M. takahasii " (9 teeth), was problematic. Following diagnoses given by Stimpson (1858, 1907), and authors such as Gordon (1931) and Shen and Dai (1964), only those with around 9 lobes or tubercles, should be considered as the true M. longipes .

Without accessing any material of M. longipes from South China, Sakai (1939) described a similar form named M. takahasii based on one male specimen from Tansui (= Danshuei), northwestern Taiwan, after the naturalist and collector, Sadae Takahashi (or Sadae Takahasi in another translation). The species was subsequently reported elsewhere in China, including Guangdong and Fujian ( Dai et al. 1986; Dai and Yang 1991) and Hong Kong ( Davie 1992). Regarding the correct spelling of the species epithet, " takahasii " (original as in Sakai 1939), instead of " takahashii " as in Sakai (1976), should be maintained (ICZN 1999: Article 32.2).

Nevertheless, M. takahasii was described with an infraorbital ridge composed of 8 tubercles and the lateral margin of the carapace cut into five teeth. Considering the original descriptions of M. longipes and M. takahasii ( Stimpson 1907 and Sakai 1939, respectively), holotypes of the two (CW 15.5 mm and 14.2 mm, respectively) differ by the numbers of lateral carapace teeth (four vs. five) of the carapace and the infraorbital lobes and tubercles (seven vs. eight). The number of infraorbital tubercles of both forms overlap might be explained by variation between intraspecific individuals (see "Note on the number of infraorbital tubercles and lobes"; Fig. 8 ), whereas the posterior-most notch along the lateral margin, however, can be very indistinct and often obscured by a layer of sediment-laden setae and easily omitted ( Davie and Nguyen 2003; see Remarks under M. tredecim below). This led Davie and Nguyen (2003: 384) to the view that M. longipes is "almost certain(ly) … a senior synonym of M. takahashii ". In enumerating Chinese species of Metaplax , Yang et al. (2008: 803), probably following Davie and Nguyen’s (2003) suggestion, listed M. takahasii as a junior synonym of M. longipes without further elaboration. In our material referred to M. longipes , the number of infraorbital tubercles and lobes varies from 7-13 for males and 14-22 in females (Table 2 ; Fig. 8 )

In the present study, we compared specimens from Hong Kong (identified as M. longipes ) and various lots from Taiwan main island (originally labeled as M. takahasii : see Materials examined above) with morphological and molecular approaches. As noted by Davie and Nguyen (2003; also see above), the number of notches (hence teeth) on the lateral margin of the carapace is easily underestimated unless the surface is carefully denuded. This aspect is well-illustrated in the case of M. tredecim (as discussed below), and also between specimens of M. longipes from Hong Kong ( Fig. 4A ) and " M. takahasii " from Danshuei, Taiwan ( Fig. 4E ), the two being identical. Molecular analyses also support only one clade of specimens from various localities of China and Taiwan (Table 1 ; Fig. 9 ).

Figures

Figure 1. Collection sites (solid symbols) for species of the genus Metaplax used in this study: green rhombus for M. elegans; red circles for M. longipes; blue triangles for M. sheni; and purple squares for M. tredecim. Empty symbols mean the additional records from references (see synonym lists for each species).

Figure 2. Metaplax elegans De Man, 1888 (A-C NCHUZOOL 15496, male, 12.7 mm), M. longipes Stimpson, 1858 (D-F ZRC 2019.0581, male, 14.9 mm), M. sheni Gordon, 1930 (G-I NCHUZOOL 15466, male, 9.9 mm), and M. tredecim Tweedie, 1950 (J-L paratype, ZRC 1964.7.14.4 - 18, 16.2 mm). A, D, G, J, A carapace B, E, H, K left infraorbital ridge C, F, I, L outer view of right cheliped. Scale bars: 1.0 mm.

Figure 4. Metaplax longipes Stimpson, 1858. A, E Dorsal view B ventral view C left infraorbital ridge D right cheliped. A-D Male (CW 15.4 mm; ZRC 2019.0581; Hong Kong) E male (CW 24.1; ZRC 1999.0708; Danshuei, northwestern Taiwan) F-H live coloration F-G male (CW 20.6 mm; NCHUZOOL 15553; Lieyu, Kinmen, Taiwan) H male (CW 23.7 mm; NCHUZOOL 15501; Hong Kong). Scale bars: 2.0 mm.

Figure 7. Metaplax elegans De Man, 1888 (A-D NCHUZOOL 15496, male, 12.7 mm), right G 1; M. longipes Stimpson, 1858 (E-H ZRC 2019.0581, male, 14.9 mm), right G 1; M. sheni Gordon, 1930 (I-L NCHUZOOL 15466, male, 9.9 mm), right G 1; and M. tredecim Tweedie, 1950 (M-P paratype, ZRC 1964.7.14.4 - 18, 16.2 mm), left G 1. Scale bars: 0.5 mm (A-H, M-P); 0.2 mm (I-L).

Figure 8. The number of infraorbital tubercles and lobes plotted as a function of carapace width (CW) of Metaplax elegans De Man, 1888, M. longipes Stimpson, 1858, M. sheni Gordon, 1930, and M. tredecim Tweedie, 1950.

Figure 9. A Bayesian inference (BI) tree for Metaplax elegans De Man, 1888, M. longipes Stimpson, 1858, M. sheni Gordon, 1930, and M. tredecim Tweedie, 1950, and the outgroups, based on the cytochrome c oxidase subunit I (COI) gene. Probability values at the nodes represent support values for BI and maximum likelihood (ML). For haplotype names, see Table 1.