Arachnothelphusa bako, Ng, 2021

Ng, Peter K. L., 2021, On two new species of arboreal crabs from phytotelms in Sarawak, Borneo (Crustacea: Brachyura: Gecarcinucidae: Arachnothelphusa), Zootaxa 5016 (3), pp. 407-418 : 413-416

publication ID	https://doi.org/ 10.11646/zootaxa.5016.3.6
publication LSID	lsid:zoobank.org:pub:369BA2BD-7673-44EC-9D54-D846F112E4A4
persistent identifier	https://treatment.plazi.org/id/A86C190B-FE78-FFC4-FF0F-2775E241F861
treatment provided by	Plazi
scientific name	Arachnothelphusa bako
status	sp. nov.

Treatment

Arachnothelphusa bako View in CoL n. sp.

( Figs. 7 View FIG , 8 View FIG , 10A–D View FIG )

Arachnothelphusa aff. kadamaiana View in CoL – Ng & Ng 2018: 99; Grinang & Ng 2021: 2. (not Potamon (Geothelphusa) kadamaianum Borradaile, 1900 ).

Material examined. Holotype: female (19.0 × 14.2 mm) ( ZRC 2002.0098 View Materials ), Bako National Park , Sarawak, coll. I. Das & L. Grismer, 27 March 2001.

Diagnosis. Carapace with dorsal surface gently surface punctate, finely granular; branchial regions inflated; epigastric and postorbital cristae distinct; cervical and H-shaped gastric grooves distinct, not confluent; anterolateral margins convex, finely granulate and serrate; antero- and posterolateral regions rugose; epibranchial tooth not discernible, margin barely separated from external orbital tooth; external orbital tooth triangular, outer margin gently concave, twice length of inner margin ( Fig. 7A, B View FIG ). Basis-ischium of third maxilliped rectangular, length to width ratio 1.59, oblique median sulcus deep ( Fig. 7D View FIG ). Outer surfaces of chelipeds gently rugose; carpus rugose, with granules, inner angle with low triangular tooth ( Fig. 7A, G View FIG ). Posterior margin of epistome less wide, median love rounded ( Fig. 7C View FIG ). P2–P5 long; merus unarmed, dorsal margin gently serrated; outer surface gently rugose; female P5 merus slightly longer than length of carapace; length to width ratio of female P4 and P5 merus 4.49–4.52 and 4.62–4.66, respectively ( Figs. 7A View FIG , 10A–D View FIG ). Vulvae large, occupying median part thoracic of sternite 6, without obvious sternal vulvar cover ( Fig. 8B View FIG ).

Etymology. The name is derived from its type locality, Bako National Park. The name is used as a noun.

Remarks. The species had previously been referred to as“ Arachnothelphusa aff. kadamaiana ” by Ng & Ng (2018) and Grinang & Ng (2021). The holotype female of A. kadamaiana is almost the same size as the holotype of A. bako n. sp., and allows for direct comparisons. Arachnothelphusa bako n. sp. can be distinguished by having the carapace proportionately narrower, the width to length ratio being 1.34 ( Fig. 7B View FIG ) (vs. 1.40 in A. kadamaiana ; Fig. 9B View FIG ); the lateral angle of the frontal margin is confluent with the rest of the margin and not visible in dorsal view ( Fig. 7B View FIG ) (vs. lateral angle clearly defined, separated from rest of frontal margin by low, wide concavity in A. kadamaiana ; Fig. 9B View FIG ); the lateral margin of the posterior margin of the epistome is proportionately shorter and only slightly convex ( Fig. 7F View FIG ) (versus margin is wider and clearly convex in A. kadamaiana ; Fig. 9F View FIG ); the basis-is- chium of the third maxilliped is proportionately shorter (length to width ratio 1.59) ( Fig. 7D View FIG ) (versus basis-ischium proportionately longer, length to width ratio 1.68; Fig. 9D View FIG ); the chela is proportionately shorter ( Fig. 7G View FIG ) (vs. proportionately longer in A. kadamaiana ; Fig. 9G View FIG ); and the female P2–P5 are proportionately shorter (e.g., length to width ratio of P4 merus 4.49–4.52; Fig. 10A, C View FIG ) (vs. legs distinctly longer, length to width ratio of P4 merus 5.45 in A. kadamaiana ; Fig. 10E View FIG ).

Compared to A. sarang from caves in Bintulu which is also superficially similar to A. bako n. sp., with similar carapace proportions and features; A. sarang can easily be distinguished by the presence of a small epibranchial tooth, a wider epistome, the median lobe of the posterior margin of the epistome is triangular, and relatively longer female ambulatory legs (cf. Grinang & Ng 2021).

Ng (1995a) recorded four species of freshwater brachyuran crabs from Bako National Park: the sesarmid Pseudosesarma bocourti (A. Milne-Edwards, 1869) , and three gecarcinucids – Perithelphusa borneensis (von Martens, 1868) , Bakousa sarawakensis Ng, 1995 , and Terrathelphusa kuchingensis ( Nobili, 1901) (all Gecarcinucidae ), the latter with doubt.

Grinang & Ng (2014, 2015) later commented that the record of “ Terrathelphusa kuchingensis ” was probably Thelphusula cristicervix ( Ng & Grinang, 2004) instead. Pseudosesarma bocourti is a species-complex of two species, the Bornean one is now P. cheirogona (Targioni Tozzetti, 1877) ( Schubart & Ng 2020) . Naruse & Ng (2007) subsequently described the arboreal sesarmid Scandarma splendidum from Bako National Park (see also Naruse & Ng 2020). The present study adds one gecarcinucid species, the arboreal Arachnothelphusa bako n. sp.