Geothelphusa boreas, Shy & Shih & Mao, 2021

Shy, Jhy-Yun, Shih, Hsi-Te & Mao, Jean-Jay, 2021, Geothelphusa boreas, a new montane freshwater crab (Crustacea: Potamidae Geothelphusa) from northeastern Taiwan, and the identity of G. hirsuta Tan & Liu, 1998, Zootaxa 5060 (1), pp. 93-104 : 96-99

Geothelphusa boreas sp. nov.

( Figs. 4–5 )

urn:lsid:zoobank.org:act:6DC2B082-D052-49B3-B243-941D38306477

Geothelphusa sp. 1 . — Shih et al. 2011: 461.

Material examined. Holotype: 1 ♂ (21.2 × 16.4 mm) (NCHUZOOL 13615), Hapen River, head branch of Danshuei (= Tansui) River, the Fushan Botanical Garden area , New Taipei City (24°45’30”N; 121°34’35”E), elevation of 740 m, coll. H.-T. Shih, 16 Feb. 1994 . Paratypes: 3 ♂♂ (15.7 × 12.4–19.0 × 14.7 mm), 2 ♀♀ (15.3 × 12.1, 17.1 × 13.1 mm) (NCHUZOOL 13429), 1 ♂ (16.2 × 13.2 mm) ( ZRC 2021.0648 ); same data as holotype. Others : 7 ♂♂ (11.4 × 9.2–15.3 × 12.2 mm), 1 ♀ (16.6 × 12.9 mm) (NCHUZOOL 13616), Dakeng Bridge, Suao , Yilan (24°31’48.3”N; 121°51’13.0”E), elevation of 280 m, coll. Y.-H. Wang et al., 8 Sep. 2010 ; 2 ♀♀ (15.1 × 10.9, 16.7 × 12.8 mm) (NCHUZOOL 16436), around the lake of Shenmihu, Nan-ao , Yilan (24°22'43.9"N; 121°44'58.7"E), elevation of 1100 m, coll. J.-J. Mao, 10 Mar. 2018 ; 1 ♂ (12.7 × 9.7 mm), 1 ♀ (13.9 × 10.5 mm) (NCHUZOOL 14998), 1 ♀ (13.5 × 10.3 mm) ( ZRC 2021.0649 ), Tongshan, Nan-ao , Yilan (24°30'15.5"N; 121°37'41.8"E – 24°30'03.5"N; 121°38'10.2"E), elevation of 1735–1880 m, coll. J.-J. Mao, 26 Sep. 2009 .

Comparative material. Geothelphusa takuan Shy, Ng & Yu, 1994 : see “Material examined” under Geothelphusa takuan ; Geothelphusa tali Shy, Ng & Yu, 1994: 1 holotype male ( NTOU F10187), Dali (= Tali), Yilan Co., Taiwan, coll. J.-Y. Shy & W.-L. Tsay, 4 Apr. 1993.

Diagnosis. Carapace length, width 1.7-, 2.3-times carapace height, respectively. Anterolateral margins distinct, lined with inconspicuous granules, without epibranchial tooth. Subterminal segment of G1 ( Fig. 3A–C ) curving inwards, outer proximal margin without tooth; terminal segment slightly curving outwards to almost straight; total length of G1 5.8 times terminal segment.

Description. Carapace ( Fig. 2A, B ) swollen longitudinally, transversely; dorsal surface smooth, glabrous, with fine pits. Carapace length, width 1.7-, 2.3-times 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 angles stout, external orbital regions concave. Anterolateral margins distinct, lined with inconspicuous granules, without epibranchial tooth. Postorbital cristae faint, smooth. Gastric, cardiac, intestinal regions smooth. H-shaped groove distinct. Tip of medium lobe of epistome stout. Distance between tip of sternopleonal cavity ( Fig. 2C ) and anterior margin of thoracic sternite 3 about 2.2 times length of thoracic sternites 1 and 2.

Chelipeds ( Fig. 2A, B ) of adult male unequal, fingers of larger chela forming obliquely triangular gape when closed. Ambulatory legs ( Fig. 2A, C ) smooth, dorsal, ventral margins of dactyli with 2 rows of small spines, respectively. Second leg about 1.8 carapace length. Telson bell-shaped, moderately short, width about 1.5 length.

Subterminal segment of G1 ( Fig. 3A–C ) curving inwards, outer proximal margin without tooth in most specimen, some smaller specimen (<13.8 mm) with low tooth, inner proximal margin slightly dilated; terminal segment slightly curving outwards to almost straight; total length of G1 5.8 times terminal segment; length of synovial membrane about 4.6 times maximum width. Outer proximal margin of basal segment of G2 ( Fig. 3D ) dilated, showing a single lobe; distal segment short, about 0.16 times total length.

Etymology. The species is derived from the Greek “ boreas ” (for north), alluding to the northernmost distribution of this species in the Central Range.

Ecological notes. The specimens were collected from the montane area with an elevation of 740 m (the Fushan Botanical Garden area) to 1100 m (Shenmihu) and about 1800 m (Tonghsan), but also extended to the coastal cliff area of Suao (elevation of 280 m) ( Fig. 1 ). The distributional range of this species covers an area of 45 km (from Fushan to Shenmihu; Fig. 1 ). There was running water in most habitats ( Fig. 2D–F ), but some crabs were more semiterrestrial, hiding under fallen leaves with only some seepage in Tongshan ( Fig. 2G, H ). Other species sympatric with this species include members of the G. eucrinodonta species complex, G. tali and G. ilan Shy, Ng & Yu, 1994 in Fushan area ( Shih et al. 2010). In the higher altitude (Tongshan and Shenmihu), the habitats of the new species are near the Fagus hayatae ( Taiwan beech) forest ( Fig. 2E–H ), with the mean (and standard deviation) water temperature 17.66 ± 2.12 oC (April 2018) and 23.25 ± 1.78 oC (May to September 2018), pH 7.4 ± 0.3 (April to October 2018) and dissolved oxygen 8.7 ± 0.9 mg /L (April to October 2018) in Shenmihu ( Fig. 2F ).

Remarks. Geothelphusa boreas sp. nov. is morphologically most similar to G. takuan and G. tali which occurs in adjacent regions in northern Taiwan. The G1 structures remain the best way to separate them. The subterminal segment of the G1 of G. tali is straight ( Shy et al. 2020: fig. 124), while those of present new species and G. takuan are distinctly curved inwards ( Figs. 3 , 4A, B ; Shy et al. 2020: fig. 121). In addition, the G1 subterminal segment in G. takuan has a distinct tooth on the outer proximal margin ( Fig. 4A ), while in G. boreas , there is usually no tooth present on the structure (or at most with a faint knob in some small individuals) ( Fig. 3A ). The distance between the tip of the sternopleonal cavity and the anterior margin of thoracic sternite 3 in G. takuan and G. tali being 1.0 times and 1.2 times the length of sternites 1 and 2, respectively, which are shorter than the ratio 2.2 times in G. boreas .

Figures

FIGURE 1. Collection sites (empty circles) for the Geothelphusa species from northern Taiwan. For locality names, see Table 1. R. = river.

FIGURE 2. Geothelphusa boreas sp. nov. A, B, C, dorsal, frontal and ventral views of the holotype (NCHUZOOL 13615); D, habitat in Dakeng Bridge, Suao, Yilan; E, F, habitat in Shenmihu, Nan-ao, Yilan; G, H, habitat in Tongshan, Nan-ao, Yilan. The arrows in E and G indicated the localities with crabs observed. The two rulers in H were used for a separate ecological study of the habitat.

FIGURE 3. Male right G1 and G2 of Geothelphusa boreas sp. nov. (holotype, NCHUZOOL 13615). A, D, ventral view of G1; B, dorsal view of G1; C, terminal segment of G1; D, ventral view of G2. Scale = 2.5 mm for A, B, D; scale = 0.5 mm for C.

FIGURE 4. Male right G1s of Geothelphusa takuan Shy, Yu & Ng, 1994 (holotype, NTOU F10205; A, B) and G. hirsuta Tan & Liu, 1998 (holotype, TMCD 3285; C, D). A, C, ventral view; B, D, dorsal view. Scale = 1 mm.

FIGURE 5. A Bayesian Inference (BI) tree of Geothelphusa boreas sp. nov. and related montane species from northern Taiwan based on cytochrome oxidase I (COI) marker. Probability values at the nodes represent the support values for BI and maximum evolution (ME). For haplotype abbreviations, see Table 1. Corresponding numbers of localities in Fig. 1 are in parenthesis behind haplotype abbreviations.