Geothelphusa siasiat , Shih, Hsi-Te, Naruse, Tohru & Yeo, Darren C. J., 2008

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, Zootaxa 1877, pp. 37-48: 39-44

publication ID

http://doi.org/ 10.5281/zenodo.184119

publication LSID

lsid:zoobank.org:pub:A69F4E18-C9A2-488A-9087-A15F2D1A6CC0

persistent identifier

http://treatment.plazi.org/id/3298B8B2-C566-4E6D-92A4-E45E0198C467

taxon LSID

lsid:zoobank.org:act:3298B8B2-C566-4E6D-92A4-E45E0198C467

treatment provided by

Plazi

scientific name

Geothelphusa siasiat
status

sp. nov.

Geothelphusa siasiat  sp. nov.

( Figs. 1View FIGURE 1, 2View FIGURE 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. G 1 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. 1View FIGURE 1 c). Male chelipeds are orange with dark brown dots ( Fig. 1View FIGURE 1 d). Female individuals tend to be more maroon ( Fig. 1View FIGURE 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. 1View FIGURE 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 G 1 ( Fig. 2View FIGURE 2 a, b) (smaller in G. candidiensis  , Fig. 4View FIGURE 4 a, b), straight subterminal segment of the G 1 ( Fig. 2View FIGURE 2 a, b) (directed outwards in G. candidiensis  , Fig. 4View FIGURE 4 a, b), and stouter ambulatory meri ( Fig. 1View FIGURE 1 a) (more slender in G. candidiensis  , Fig. 3View FIGURE 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. 11 c –f) illustrated of the G 1 of G. candidiensis  from Dihli, Nantow Hsien (=Dili, Nantou County) ( NTOU F 10090View Materials, 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. 4View FIGURE 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 G 1 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 G 1 s 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 G 1 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. 1View FIGURE 1 a, b, 2 a –d; Shy et al., 1994: figs. 13 a –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 G 1 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. 1View FIGURE 1 a, b, 2 a –d; Shy et al., 1994: figs. 23 a –e).

Geothelphusa siasiat  sp. nov. is also very similar in carapace and the morphology of the G 1 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 G 1 with a more slender, more sinuous terminal segment and broader subterminal segment, with strong proximal tooth on the outer margin (G 1 terminal segment stouter, less sinuous, subterminal segment slenderer, with very low proximal tooth on the outer margin in G. nanhsi  ) ( Figs. 1View FIGURE 1 a, b, 2 a –d; Shy et al., 1994: figs. 22 a –e).

DNA analysis

A 556 -bp segment (excluding the primer regions) of 16 S 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 16 S 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 16 S rRNA and COI (in parentheses) and differences in the total bp numbers (gaps considered) are shown in Table 2. For 16 S 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. (2007 b) studied the systematics of Geothelphusa  from southwestern Taiwan based on 16 S 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 16 S rRNA and ≥ 11 bp (1.8 %) of COI ( Shih et al. 2007 b). 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 16 S 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 16 S 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. 2007 b). 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 16 S 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.

NMNS

National Museum of Natural Science

ZRC

Zoological Reference Collection, National University of Singapore

NTOU

Institute of Marine Biology, National Taiwan Ocean University

DNA

Department of Natural Resources, Environment, The Arts and Sport

COI

University of Coimbra Botany Department