Scopimera curtelsona Shen, 1936

Hui, T. Y. & Wong, Kingsley J. H., 2019, Tropical sand-bubblers heading north? First discovery of Scopimera curtelsona Shen, 1936 (Crustacea: Decapoda: Dotillidae) populations in Hong Kong: possible range expansion from Hainan, China, Zootaxa 4652 (3), pp. 520-532 : 522-523

Scopimera curtelsona Shen, 1936

( Figs. 2 , 3 )

Scopimera curtelsona Shen, 1936: 73 , text-fig. 4.— Shen 1940b: 73.— Shen & Dai 1964: 123, 1 un-numbered fig.— Wong et al. 2011: 27, figs. 5e–g, 6c–d.

Scopimera curtelsoma .— Dai et al. 1986: 454, fig. 254, pl. 63(8).— Dai & Yang 1991: 498, fig. 254(1), pl. 63(8).—Z. Huang 1994: 596 [list].—P. K. L. Ng et al. 2008: 235 [list]. (for “ curtelsoma ” see Wong et al. 2011)

Scopimera curtelson .— Yang et al. 2008: 805 [list].

Material examined. 1♂ ( CEL), Starfish Bay , Hong Kong, 2002, coll. D.Y.N. Poon ; 1♀ ( CEL), Starfish Bay , Hong Kong, 9 Sep 2008, coll. K.J.H. Wong ; 4♂♂ (SWIMS-CRU-13-001), Shui Hau , Hong Kong, 11 Aug 2013, coll. T.Y. Hui ; 14 ♂♂ 2 ♀♀ (SWIMS-CRU-16-001), Lung Mei , Hong Kong, 16 Sep 2016, coll. K. Wong ; 1♂ (SWIMS-CRU- 16-002), Lung Mei, Hong Kong, 16 Sep 2016, coll. K. Wong; 1 ♂ ( KJHW personal collection), Ting Kok , Hong Kong, 22 Aug 2017 , coll. K. Wong.

Other material: Scopimera curtelsona . 12 ♂♂ 18 ♀♀ (CEL-Sco-Hainan-001), Wenchang, Hainan, China, 2 Dec 2008, coll. K.J.H. Wong, S.-L. Yang & K.H. Lo.

Scopimera intermedia . 27 ♂♂ (CEL-Sco-HK-008), Starfish Bay , Hong Kong, Sep 2008, coll. K. Wong ; 4 ♂♂ 1 ♀ (CEL-Sco-HK-009), Bui O, Hong Kong, Sep 2008, coll. K. Wong.

Diagnosis. Carapace inflated, globular, broader than long, surface generally smooth ( Figs. 2 and 3 ). Maxilliped 3 merus slightly shorter than ischium, joint between merus and ischium oblique ( Fig. 3b ). Chelipeds equal, in adult males total length less than 1.5 times carapace length, carpus rhomboid ( Fig. 2b ), chela movable finger armed with distinct, broad triangular molar along cutting margin ( Fig. 3c ). G1 slender, recurved dorsally, tapering into rounded tip ( Fig. 3e ), orienting slightly laterally in ventral view ( Fig. 3f ), distal opening fringed with stiff setae of subequal lengths ( Figs. 3e and f ).

Live colouration. Overall creamy white, tinted caramel, mottled with dark brown and speckled with whitish spots. Tips of chela fingers vaguely reddish in some individuals. Ambulatory legs pale yellow with faint brownish bands ( Fig. 2 ). Carapace colour somewhat variable, possibly caused by the colour of feeding substrates, light condition and temperature.

Distribution. Hainan Island (type locality: New Town Bay, Hainan Island) and Hong Kong (present report).

Ecological remarks. Locally at Shui Hau, where Scopimera curtelsona , S. intermedia and Dotilla wichmanni were sympatric, the median particle size decreased progressively from the high to low shore, being classified as medium sand at both the high (0.403 ± 0.053 mm, mean ± SE, Wentworth scale), and mid shores (0.326 ± 0.079 mm), to fine sand at the low shore (0.140 ± 0.003 mm, ANOVA, F 2,15 = 6.1, P = 0.01, Fig. 4 ). Sediment organic content showed the opposite trend, increasing from 1.78 ± 0.06 % at the high shore, 2.35 ± 0.14 % at the mid shore, to 2.93 ± 0.13 % at the low shore ( ANOVA, F 2,15 = 24.4, P <0.001, Fig. 4 ). Water content of the sediments, however, was similar among tidal heights and averaged at 22.1 ± 0.2 % ( ANOVA, F 2,15 = 0.1, P> 0.05).

Scopimera curtelsona were found along all tide levels sampled in Shui Hau, but their density differed significantly between levels, with the highest abundance along the mid-shore (Poisson regression, χ 2 2 = 35, P <0.001, Fig. 4 ). Scopimera intermedia was more restricted in distribution, being found only at the high shore with an average density of 0.9 ± 0.3 individuals per 0.0625 m 2 (mean ± SE, Fig. 4 ). Dotilla wichmanni was distributed only along both the mid and low shores in 2013, averaging at 0.5 ± 0.3 individuals per 0.0625 m 2. The population survey, however, did not cover the entire shore as burrows of S. curtelsona and D. wichmanni also occurred further downshore (i.e. <1.5 m + C.D.). The qualitative sampling in 2018 revealed similar patterns in dotillid distribution, with S. intermedia being restricted to the high shore ( Fig. 4 ), and S. curtelsona and D. wichmanni were distributed across all three heights, but S. curtelsona was ~16 times more abundant than D. wichmanni when pooling across all samples.

All three dotillids in Shui Hau possessed spoon-shaped setae in the second maxillipeds as noted by previous workers ( Fig. 5 ; see also Ono 1965; Vogel 1984), but the setae morphology of Dotilla wichmanni was different from both Scopimera species. Spoon-tip size of both Scopimera species were larger than that of D. wichmanni by ~90% when corrected for variation in body size (F 2,20 = 33.9, P <0.001). The setal spoons in D. wichmanni were more triangular instead of being rectangular as in Scopimera . Whilst there were both plumose and spoon-shaped setae in the second maxillipeds of Scopimera , D. wichmanni lacked plumose setae and only possessed spoon-shaped setae. The spoon-shaped setae in D. wichmanii , however, were lined with two patches of fine hairs on either side which were absent in Scopimera ( Fig. 5 ).

Figures

FIGURE 2. Live colouration of Scopimera curtelsona Shen, 1936: (a) male, Shui Hau, Hong Kong; (b) male, Lung Mei, Hong Kong (SWIMS-CRU-16-002).

FIGURE 3. Scopimera curtelsona, male (10.1 × 7.0 mm, SWIMS-CRU-16-002, Lung Mei): (a) carapace, dorsal view; (b) left third maxilliped, external view; (c) left chela, external view; (d) male pleon; (e) left G1, mesial view, (f) tip of left G1, ventral view.

FIGURE 4. Sediment characteristics (a) and dotillid density (b) on the shore in Shui Hau, Hong Kong, where Scopimera intermedia, S. curtelsona and Dotilla wichmanni coexist. H = high (~ 2.1 m + C.D.), M = mid (~ 1.8 m + C.D.) and L = low tidal height (~ 1.5 m + C.D.). n = 6 replicates for sediment characteristics and n = 8 replicates for crab density along each height. Error bars are SE. No D. wichmanni were found along the high shore during the survey in 2013. Pie charts show the relative abundance of the three dotillids along each height during the qualitative sampling in 2018 (white = S. intermedia, black = S. curtelsona, grey = D. wichmannii), numbers next to the charts are total number of crabs collected along each tidal height.

FIGURE 5. Scanning electron micrographs of the second maxillipedal setae of (a) Scopimera curtelsona, (b) S. intermedia and (c) Dotilla wichmanni. Graph (d) showing the variation in spoon-tip size against body size among the three species.