Geothelphusa cilan, Shy & Shih & Mao, 2014

Shy, Jhy-Yun, Shih, Hsi-Te & Mao, Jean-Jay, 2014, Description of a new montane freshwater crab (Crustacea: Potamidae: Geothelphusa) from northern Taiwan, Zootaxa 3869 (5), pp. 565-572 : 567-568

Geothelphusa cilan sp. nov.

( Figs. 1–2 )

Geothelphusa sp. 2 —Shih et al. 2011: 461.

Material examined. Holotype: 1 ♂ (18.8 x 14.4 mm) (NCHUZOOL 13617), Cilan , Takejin (= Takazinm ) River , the headstream of Danshuei (= Tansui ) River , Jianshih , Hsinchu County (near Yilan [= Ilan] County), Taiwan, 24°32’08.7”N; 121°23’09.7”E, elevation of 1950 m, coll. H.- T. Shih & J.-J. Mao, 28 March 2009.

Paratypes: 2 ♂♂ ( CW 12.4–13.5 mm) , 3 ♀♀ (13.8–15.5 mm) (NCHUZOOL 13430); 2 ♂♂ (10.4–20.6 mm) (NCHUZOOL 13618); 1 ♂ (13.4 mm) (NCHUZOOL 13619); 5 ♂♂ (15.5–18.9 mm), 13 ♀♀ (14.5–19.3 mm) (NCHUZOOL 13620), same data as holotype .

Comparative material. Geothelphusa monticola Shy, Ng & Yu, 1994: 1 holotype male ( NTOU F10204), Siaoyako (= Sheauyeakow), Heping (= Hoping), Taichung City, Taiwan, coll. J.-Y. Shy & W.-L. Tsay, 6 Jun. 1992; Geothelphusa takuan Shy, Ng & Yu, 1994: 1 holotype male ( NTOU F10205), Daguan (= Takuan), Fusing (= Fuhsing), Taoyuan County, Taiwan, coll. J.-Y. Shy & W.-L. Tsay, 1 Nov. 1992 .

Description. Carapace ( Fig. 2A–B ) swollen longitudinally, transversely; dorsal surface smooth, glabrous, with fine pits. Carapace length, width 1.7, 2.2 carapace height, respectively. Frontal margin slightly dived into 2 lobes, without tooth. Postorbital cristae distinct, supraorbital margin smooth, without granules; infraorbital margin smooth to almost smooth, lined with inconspicuous granules. External orbital angle stout, external orbital region concave. Anterolateral margin distinct, lined with inconspicuous granules, without epibranchial tooth. Postorbital crista faint, smooth. Gastric, cardiac, intestinal regions smooth. H-shaped groove distinct. Tip of medium lobe of epistome stout. Distance between tip of closed male abdomen, anterior margin of thoracic sternite 3 about 1.1 length of thoracic sternites 1, 2 ( Fig. 2C ).

Chelipeds of adult males unequal, fingers of larger chela forming obliquely triangular gape when closed. Ambulatory legs smooth, dorsal, ventral margins of dactyli with 2 rows of small spines, respectively. Second leg about 1.8 carapace length. Telson of male abdomen bell-shaped, moderately short, width about 1.4 length ( Fig. 2C ).

Subterminal segment of G1 ( Fig. 1A–C ) curving inwards, outer proximal margin with small tubercle, inner proximal margin clearly dilated; terminal segment slightly curving inwards to almost straight (length /width = 2.4); total length of G1 5.5 terminal segment; length of synovial membrane about 3.3 maximum width. Outer proximal margin of basal segment of G2 ( Fig. 1D ) dilated, showing a single lobe; distal segment short, about 0.12 total length.

Etymology. The species is named for the type locality, the Cilan Forest, in northern Taiwan. The name is used as a noun in apposition.

Coloration. Carapace and ambulatory legs grayish brown, mottled with dark brown spots; chelae orange-red, with dark brown spots; tip and inner edge of fingers white ( Fig. 2D–G ).

Ecological notes. The specimens were collected from the headstream of Danshuei River ( Fig. 2H ) near the boundary of Hsinchu and Yilan counties, near Yuanyang Lake Nature Reserve, with an altitude about 2000 m. The mean monthly water temperatures were 10.3–14.6°C during April to December, 2012 (mean 12.6°C) for the adjacent Yuanyang Lake, with the same drainage.

Remarks. Geothelphusa cilan sp. nov. is similar to G. monticola and G. takuan both of which are present in the adjacent regions. The subterminal segment of the G1 of G. monticola is slightly S-shaped, and those of G. takuan and G. cilan sp. nov. are slightly curved inwards, but G. monticola and G. takuan have a conspicuous tubercle and G. cilan sp. nov. a small tubercle at the outer proximal margin. The terminal segment of the G1 of G. monticola is slender (length/width = 3.3), and those of G. takuan and G. cilan sp. nov. are stouter (length/width = 1.8 and 2.4, respectively). Geothelphusa takuan and G. cilan sp. nov. have shorter distance between the tip of the closed male abdomen and anterior margin of thoracic sternite 3 (ratio = 1.0 and 1.1, respectively) than that in G. monticola (ratio = 1.6).

DNA analyses and discussion. A 616-658 basepair (bp) segment of the COI was amplified from 9 specimens of G. cilan and 10 specimens of the closely related G. monticola , resulting in 5 different haplotypes ( Table 1 ). The studied segment was AT rich (63.2%) (T, 35.4%; A, 27.8%; G, 16.5%; and C, 20.3%). In this gene, 18 positions were variable and 13 parsimoniously informative.

The phylogenetic tree constructed by BI and ML methods ( Fig. 3 ) supports the clade of G. cilan sp. nov., which is a sister species to another montane clade, G. monticola . The pairwise nucleotide divergences for COI with K2P distance is shown in Table 2 . The mean interspecific K2P distance of G. cilan is 2.26% with G. monticola , which is 38 or 17 times greater than the mean intraspecific distance of G. cilan (0.06%) or G. monticola (0.13%), respectively ( Table 2 ). The lowest interspecific K2P distance of G. cilan is 2.15% with G. monticola , which is 13 or 4.7 times greater than the largest intraspecific distance of G. cilan (0.16%) or G. monticola (0.46%). The interspecific K2P distance of 2.15% – 2.65% between G.cilan sp. nov. and G. monticola is not high, but still higher than the distance between G. marginata Naruse, Shokita & Shy, 2004 and G. fulva Naruse, Shokita & Shy, 2004 (1.48%–1.99%, Shih et al. 2011); and the distance among G. makatao Shih & Shy, 2009 , G. shernshan Chen, Cheng & Shy, 2005 , and G. pingtung Tan & Liu, 1998 (1.65%–1.98%, recalculated from Shih & Shy 2009).

Although the nearest distance between the localities of G. cilan sp. nov. and G. monticola (see nos. 32 and 27 in fig. 1 of Shih et al. 2011) is only about 13 km, both areas belong to different drainages, the Danshuei and Daja rivers, respectively. Furthermore, several mountains more than 2000 m a.s.l. separated the two areas. Based on the substitution rates of 2.33% per 10 6 yr for COI of terrestrial crabs (see Schubart et al. 1998), the two sister species diverged at 1.0±0.2 million years ago (mya) (with uncorrected p-distance divergences of 2.35%±0.56%), which is quite young allopatric speciation, considering the geological history of Taiwan is about 5 mya (see Shih et al. 2006).

Figures

FIGURE 1. Male right first and second gonopods of Geothelphusa cilan sp. nov. (holotype, NCHUZOOL 13617). A, ventral view of right G1; B, dorsal view of right G1; C, terminal segment of G1; D, ventral view of right G2. Scale = 1 mm for A, B, D; scale = 0.5 mm for C.

FIGURE 2. Geothelphusa cilan sp. nov. A, B, C, dorsal, frontal and ventral views of the holotype (NCHUZOOL 13617); D–G, live coloration of the male, dorsal view (D, E) and frontal view (F, G); D, F, NCHUZOOL 13618 (CW 20.6 mm); E, G, NCHUZOOL 13620 (CW 15.5 mm); H, habitat in a montane creek in the headstream of Danshuei River, Jianshih, Hsinchu County.

FIGURE 3. A Bayesian Inference (BI) tree of Geothelphusa cilan sp. nov. and related montane species from northern Taiwan based on cytochrome oxidase I (COI) marker. Probability values at the nodes represent confidence values for BI and maximum likelihood (ML). For haplotype abbreviations, see Table 1.