Geothelphusa siasiat Shih, Naruse & Yeo, 2008, sp. nov.
Creators: name: Shih, Hsi-Te
name: Naruse, Tohru
name: Yeo, Darren C. J.
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Potamidae
Geothelphusa
Geothelphusa siasiat

description: Geothelphusa siasiat sp. nov.
(Figs. 1, 2)
Material examined. Holotype: male (16.7 x 13.3 mm) (NMNS 5688-001), Fengsiang waterfall, Hengshan, Hsinchu, Taiwan, elevation of 700 m, coll. Jiun-Nan Huang, 9 Dec. 2000. Paratypes: 1 female (21.4 x 15.9 mm) (NCHUZOOL 13157), same data as holotype; 2 males (14.2 x 10.9, 17.6 x 13.6 mm), 2 females (19.3 x 15.2, 22.1 x 16.8 mm) (NCHUZOOL 13158), same data as holotype; 1 female (21.9 x 16.5 mm) (NCHU- ZOOL 13159), same data as holotype; 1 male (16.6 x 12.8 mm) (ZRC 2008.0010), same data as holotype; 2 males (14.1 x 10.9, 15.0 x 11.4 mm), 2 females (17.3 x 13.2, 19.5 x 14.4 mm) (ZRC 2008.0011), Baguali River, Tai-an, Miaoli, Taiwan, 700 m, coll. Hsi-Te Shih, 25 Jan. 2002; 4 males (10.4 x 8.13 – 13.4 x 10.2 mm), 12 females (12.4 x 9.64 – 18.6 x 13.9 mm) (NCHUZOOL 13160), Baguali River, Tai-an, Miaoli, Taiwan, 700 m, coll. H.-T. Shih, 25 Jan. 2002.
Comparative material: See Appendix 1.
Diagnosis. Carapace relatively flat, low, transverse; epigastric cristae relatively low, weakly developed, gastric and branchial regions gently swollen; external orbital angle broadly triangular; epibranchial tooth barely discernible; anterolateral margin distinctly cristate and granular in appearance; branchial region rugose. Eye-stalk slender, with relatively small cornea. Ambulatory legs of normal length, hairy; dactyli relatively stout. Anterior thoracic sternum broad, with gently convex suture between thoracic sternites 3 and 4. Male abdomen relatively broad in appearance, with lateral margins almost straight; telson with gently concave lateral margins. G1 terminal segment gently but distinctly sinuous in appearance; subterminal segment relatively broad, with strong proximal rounded tooth on the outer margin.
Etymology. The new species is named after the aboriginal tribe, the Siasiat, who dwell only in a small area in the mountains between Hsinchu and Miaoli counties, which is also the distributional range of this new species. The name is used as a noun in apposition.
Coloration. Carapace and ambulatory legs are greenish-grey or maroon, with scattered dark brown dots (Fig. 1 c). Male chelipeds are orange with dark brown dots (Fig. 1 d). Female individuals tend to be more maroon (Fig. 1 e).
Ecological notes. The Miaoli specimens of G. s i a s i a t sp. nov. were collected under cobbles near the bank of an upstream creek, about 2 m wide (Fig. 1 f) at an altitude of approximately 700 m. Geothelphusa siasiat sp. nov. is sympatric with Candidiopotamon rathbunae (De Man, 1914) but the latter prefers to hide submerged under larger rocks in the stream.
Distribution. The new species is found in the mountainous region of Hsinchu and Miaoli counties, northwestern Taiwan.
Remarks. Geothelphusa siasiat sp. nov. is characterized by its small size, the largest specimen being only 22.1 x 16.8 mm (NCHUZOOL 13158, adult female with fully expanded abdomen). Geothelphusa candidiensis Bott, 1967, described from the Candidius Sea (presently known as Sun Moon Lake or Rihyuetan), Nantou County, is superficially similar to G. siasiat sp. nov., and is the only small-sized species that has been reported from Hsinchu County where G. s i a s i a t sp. nov. is present (Shy et al. 1994). Our comparison of the type specimen of G. candidiensis against G. s i a s i a t sp. nov. specimens from Hsinchu and Miaoli Counties, however, revealed that G. s i a s i a t sp. nov. clearly differs from G. candidiensis by the strong outer basal tooth of the subterminal segment of the G1 (Fig. 2 a, b) (smaller in G. candidiensis, Fig. 4 a, b), straight subterminal segment of the G1 (Fig. 2 a, b) (directed outwards in G. candidiensis, Fig. 4 a, b), and stouter ambulatory meri (Fig. 1 a) (more slender in G. candidiensis, Fig. 3 a). In general, freshwater crabs tend to have relatively narrow geographical distribution (Shih et al. 2004, 2007b) but Geothelphusa siasiat sp. nov. and G. candidiensis have similar habitats (See “Ecological notes” above; Shy et al. 1994: 809; Shy & Yu, 1999: 36) and both have been recorded from close areas in Hsinchu County (See “Distribution” above; Shy et al. 1994: fig. 30). Since the type locality of G. candidiensis is about 90 km away from where Shy et al. (1994) recorded “ G. candidiensis ” in Hsinchu, and the locality is within the distributional area of G. s i a s i a t sp. nov., it is possible that the “ G. candidiensis ” from Hsinchu is G. s i a s i a t sp. nov. instead.
Shy et al. (1994: fig. 11c–f) illustrated of the G1 of G. candidiensis from Dihli, Nantow Hsien (=Dili, Nantou County) (NTOU F10090, 28.0 x 22.3 mm), near the type locality of G. candidiensis. The drawings show a shorter and stouter appearance when compared with the holotype of G. candidiensis (Fig. 4 a–d). We examined Shy et al.’s (1994) specimen and confirmed that their drawing is accurate. This range of morphological variation of the G1 suggests that G. candidiensis may be a species complex and is in need of revision. This, however, is beyond the scope of the present study, and we tentatively treat the specimens with short and stout G1s as G. candidiensis. In any case, the above mentioned differences between G. siasiat sp. nov. and the type specimen of G. candidiensis also apply to the specimen from Dili.
In addition to G. candidiensis, G. siasiat also superficially resembles G. tali Shy, Ng & Yu, 1994, G. tawu Shy, Ng & Yu, 1994, and G. nanhsi Shy, Ng & Yu, 1994, as well. Geothelphusa siasiat sp. nov. can be distinguished from G. tali by some external differences such as the relatively lower and weaker epigastric cristae, which are divided by a shallower groove (epigastric cristae relatively higher and stronger, with deeper groove in between in G. t a l i); relatively broader male abdomen, with flatter segments (narrower, with higher segments in G. t a l i); relatively stout ambulatory leg dactyli (relatively more slender in G. tali); as well as by G1 differences seen in the narrower tip of the terminal segment (broader terminal segment in G. t a l i) and subterminal segment being gently curved outwards (subterminal segment sinuous, but appearing bent, not curved in G. tali) (Figs. 1 a, b, 2a–d; Shy et al., 1994: figs. 13a–e). Likewise, G. siasiat sp. nov. can be differentiated from G. t a w u by the telson of the male abdomen having gently concave lateral margins (almost straight in G. t a w u) and by the sinuous, relatively stouter G1 terminal segment being distinctly or sharply narrowed at the tip (terminal segment straight, relatively slenderer and gradually tapered towards the tip in G. t a w u) and basal part of the subterminal segment being broader than in G. t a w u (Figs. 1 a, b, 2a–d; Shy et al., 1994: figs. 23a–e).
Geothelphusa siasiat sp. nov. is also very similar in carapace and the morphology of the G1 to G. nanhsi Shy, Ng & Yu, 1994. Individuals of the new species are distinctly smaller in size and the two species can be easily separated by the size difference, e.g., a female of G. siasiat sp. nov. measuring 21.4 x 15.9 mm (NCHU- ZOOL 13157) is clearly a mature adult with a fully expanded abdomen while a similar-sized female of G. nanhsi measuring 22.1 x 17.5 mm (NCHUZOOL 13149) still lacks the expanded abdomen of a mature adult female. In addition, the new species can also be separated from G. nanhsi by several morphological characters including a flatter, lower carapace, which is more transverse in shape (carapace more convex longitudinally, higher, more squarish in shape in G. nanhsi); hairy ambulatory legs (glabrous in G. nanhsi); stouter dactyli of the ambulatory legs; broader male anterior thoracic sternum (narrower and deeper in G. nanhsi); and G1 with a more slender, more sinuous terminal segment and broader subterminal segment, with strong proximal tooth on the outer margin (G1 terminal segment stouter, less sinuous, subterminal segment slenderer, with very low proximal tooth on the outer margin in G. nanhsi) (Figs. 1 a, b, 2a–d; Shy et al., 1994: figs. 22a–e).
DNA analysis
A 556-bp segment (excluding the primer regions) of 16S rRNA from 17 specimens was amplified and aligned. Of these, 69 positions were variable and 27 parsimoniously informative, and 13 different haplotypes were distinguished (Table 1). The studied segment of the 16S rRNA sequences was AT rich (72.4%) (37.0% T, 35.4% A, 17.3% G, and 10.3% C). For the COI gene from 16 specimens, a 616-bp segment was compared, resulting in 14 different haplotypes (Table 1). The studied segment of the COI sequences was also AT rich (66.6%) (37.6% T, 29.0% A, 15.2% G, and 18.2% C). In this gene fragment, 145 positions were variable and 74 were parsimoniously informative.
The pairwise nucleotide divergences for 16S rRNA and COI (in parentheses) and differences in the total bp numbers (gaps considered) are shown in Table 2. For 16S rRNA, the genetic distances within the four main clades (G. s i a s i a t sp. nov., G. candidiensis, G. aff. olea, and G. o l e a clade) (ranging from 0 to 0.37%, mean=0.24%) was significantly lower than that between species (from 0.37 to 1.66%, mean=1.14%) (p <0.01, Mann-Whitney U-test). The mean number of differences within species (from 0 to 3, mean=1.96) also was significantly lower than that between species (from 2.5 to 16, mean=11.5) (p = 0.05, Mann-Whitney Utest). For the COI gene, the genetic distance within each main clade (from 0 to 0.82%, mean=0.60%) was significantly lower than that between species (from 1.56% to 4.53%, mean=3.41%) (p <0.01, Mann-Whitney Utest); and the mean number of differences within species (from 0 to 5, mean=3.67) was also significantly lower than that between species (from 9.5 to 26.83, mean=20.39) (p <0.01, Mann-Whitney U-test).
within clade between clades Shih et al. (2007b) studied the systematics of Geothelphusa from southwestern Taiwan based on 16S rRNA and COI genes. They concluded that the G. o l e a clade (G. o l e a -like species viz. G. caesia, G. nanhsi, G. olea, G. tsayae, and G. wutai) from Chiayi County to northwestern Pingtung County are possibly conspecific. Previous phylogenetic studies on potamids (Shih et al. 2004, 2005, 2006, 2007b) have suggested that, with respect to the relationship and topology in the phylogenetic tree, distinct species differ by ≥ 5 bp (0.9%) of 16S rRNA and ≥ 11 bp (1.8%) of COI (Shih et al. 2007b). The molecular data in the form of bp differences between G. siasiat sp. nov. and other examined species exceed the expected differences between species (Table 2), providing further support for the establishment of the new species. Despite the strong morphological similarity between G. s i a s i a t sp. nov. and G. candidiensis (see Remarks), G. s i a s i a t sp. nov. is genetically closer to G. aff. olea and G. o l e a clade. Geothelphusa siasiat sp. nov. differs from G. aff. olea by an average of 5.8 (24) bp and 0.87% (4.02%) divergence in 16S rRNA (COI), and differs from the G. o l e a clade by an average of 6.3 (21.8) bp and 0.87% (3.66%) in 16S rRNA (COI). Additionally, the present molecular analysis indicates that the G. olea clade from southwestern Taiwan includes some species which have been suggested as synonymies (Shih et al. 2007b). It is also clarified that specimens identified as G. aff. olea (from centro-western Taiwan) differ from the G. o l e a clade (from southwestern Taiwan), by an average of 2.5 bp in 16S rRNA and 9.5 bp in COI (Table 2), suggesting that it may in fact be a geographical subspecies. However, more studies will be needed to confirm this.
description: Published as part of Shih, Hsi-Te, Naruse, Tohru & Yeo, Darren C. J., 2008, A new species of Geothelphusa Stimpson, 1857, from Taiwan (Crustacea: Brachyura: Potamidae) based on morphological and molecular evidence, with notes on species from western Taiwan, pp. 37-48 in Zootaxa 1877 on pages 39-44, DOI: 10.5281/zenodo.184119