Geosesarma sodalis, Ng, 2021
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publication ID |
https://dx.doi.org/10.3897/zookeys.1031.63134 |
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publication LSID |
lsid:zoobank.org:pub:15B4DD80-14BD-42EA-BB6D-11E8FE9392BA |
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persistent identifier |
https://treatment.plazi.org/id/69A4BE4D-8B0B-4243-9B2D-BA1D559A2C28 |
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taxon LSID |
lsid:zoobank.org:act:69A4BE4D-8B0B-4243-9B2D-BA1D559A2C28 |
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treatment provided by |
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scientific name |
Geosesarma sodalis |
| status |
sp. nov. |
Geosesarma sodalis sp. nov. Figures 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3
Material examined.
Holotype: male (10.1 × 9.8 mm) (ZRC 2020.0413), limestone cave, Bukit Sarang, Bintulu, Sarawak, Malaysia, coll. Stuebing RB, early 2005.
Diagnosis.
Carapace quadrate, slightly wider than long, width to length ratio 1.03, lateral margins gently concave, subparallel (Fig. 1A, B View Figure 1 ); dorsal surfaces with well-defined regions, anterior half with low granules, posterior half almost smooth (Fig. 1A, B View Figure 1 ); frontal margin distinctly deflexed, frontal lobes broad, with truncated margins in dorsal view, separated by wide shallow median concavity; postfrontal and postorbital cristae sharp, distinct (Fig. 1A-C View Figure 1 ); external orbital angle triangular, directed obliquely anteriorly, extending just beyond lateral carapace margins, outer lateral margin convex; separated from first epibranchial tooth by deep V-shaped cleft; first epibranchial tooth distinct, second epibranchial tooth visible only as low lobe, barely separated from first tooth by shallow concavity (Fig. 1A, B View Figure 1 ); merus of third maxilliped subovate; exopod slender, flagellum absent (Fig. 3A View Figure 3 ); outer surfaces of palm of chela covered with small rounded granules, inner surface without transverse ridge; fingers longer than palm, dorsal margin of dactylus with 10 or 11 sharp, anteriorly directed sharp tubercles (Fig. 2A-D View Figure 2 ); ambulatory merus with sharp subdistal spine on dorsal margin, surface weakly rugose, propodus slender, relatively long (Figs 1A View Figure 1 , 2E, F View Figure 2 ); pleon triangular; somite 3 widest, somite 6 with lateral margins gently convex; telson triangular, longer than broad, lateral margins gently convex (Fig. 2G View Figure 2 ); G1 relatively slender, proximal, distal part bent at angle of ca. 45° along longitudinal axis, subdistal part of outer margin gently angular with shelf-like feature (Figs 2H-K View Figure 2 , 3B-D, F View Figure 3 ), distal part elongate, tapering in lateral view, spatuliform in marginal view, with small submedian cleft at tip when viewed mesially (Fig. 3E, G View Figure 3 ).
Colour.
Not known.
Females.
Not known.
Etymology.
The name is derived from the Latin noun for comradeship; alluding to the deep friendship the author has had over the last 30 years with the collector, Rob Stuebing, who has collected many interesting species for him.
Remarks.
The island of Borneo has 13 known species of Geosesarma , all of which are endemic to the island. Five species occur in the state of Sarawak ( Ng and Grinang 2018; Ng and Ng 2019). One group of Geosesarma species is characterised by their relatively quadrate carapace, presence of a row to sharp tubercles on the dorsal margin of the cheliped dactylus, absence of a flagellum on the third maxilliped exopod, and a relatively stout G1 with a tapering corneous distal part (in lateral view). In Borneo, the species in this group are G. gracillimum (De Man, 1902), G. sabanus Ng, 1992, G. aurantium Ng, 1995, G. katibas Ng, 1995, G. danumense Ng, 2002, G. bau Ng & Grinang, 2004, G. ambawang Ng, 2015, G. pontianak Ng, 2015, G. larsi Ng & Grinang, 2018, and G. spectrum Ng & Ng, 2019.
Five of the species in this group are present in Sarawak and Brunei: G. gracillimum , G. katibas , G. bau , G. larsi , and G. sodalis sp. nov. Compared to G. gracillimum , the carapace of G. sodalis sp. nov. is more quadrate with the lateral margins subparallel (Fig. 1A, b View Figure 1 ) (versus gently diverging in G. gracillimum ; see Ng 2015: fig. 14A, B; Ng and Ng 2015: fig. 5F). The G1 of G. sodalis sp. nov. (Figs 2H, I View Figure 2 , 3B, C View Figure 3 ) is distinct in that it is proportionately more slender than those of G. gracillimum , G. katibas , and G. larsi (cf. Ng 1995: fig. 12A-E; Ng and Grinang 2018: fig. 5B-F, Ng and Ng 2019: fig. 9B-E, G, H, I-M). In addition, the distal corneous part of the G1 is almost straight in G. sodalis sp. nov. (Fig. 3B-D, F, H-K View Figure 3 ) but gently upcurved in G. gracillimum (see Ng and Ng 2019: fig. 9I-M). Compared to G. bau , which also has a more slender G1, G. sodalis sp. nov. has the distal part bent at an angle of about 45° along the longitudinal axis and the subdistal part of the outer margin is more angular and shelf-like (Figs 2H-K View Figure 2 , 3B-D, F View Figure 3 ) (versus G1 bent at about 30° along longitudinal axis and subdistal part of outer margin is gradually sloping in G. bau ; see Ng and Grinang 2004: fig. 9D, F).
The relatively longer fingers (distinctly longer than the palm) and the outer surface of the chela with fewer small granules in G. sodalis sp. nov. (Fig. 2A-D View Figure 2 ), differ from the condition in G. katibas and G. larsi , with the shorter fingers and the outer surface densely covered with small rounded granules (see Ng and Grinang 2018: figs 2D, 3A; Ng and Ng 2019: fig. 1C). The longer fingers of the chela most closely resemble those of G. gracillimum and G. bau (see Ng 1995: fig. 13A; Ng and Grinang 2004: fig. 8A; Ng 2015: fig. 14E, F). The male pleon of G. sodalis sp. nov. (Fig. 2G View Figure 2 ) is similar to that of G. katibas (see Ng and Ng 2019: fig. 8D), but this character is not reliable to differentiate taxa as it varies some degree in relative widths of the somites and convexity of the lateral margins of somite 6 ( Ng and Ng 2019).
The male chela and G1 differences between G. sodalis sp. nov. and G. spectrum (from Brunei) are the same as for the Sarawakian G. katibas . Geosesarma sodalis sp. nov. differs markedly from the two species in this group from Indonesian Kalimantan, G. ambawang and G. pontianak , in possessing a G1 that is proportionately stouter and the subdistal part of the outer margin has a prominent right angled hump-like arch (see Ng 2015: figs 9D-G, 13D-H, J-M). The three species in this group from the eastern Malaysia state of Sabah, G. sabanus , G. aurantium , and G. danumense differ markedly from G. sodalis sp. nov. in that the corneous G1 distal part is longer and distinctly spatuliform in lateral view ( Ng 1992, 1995, 2002; Ng and Ng 2018).
Biology.
Noteworthy is that G. sodalis sp. nov. was collected inside a cave where a cavernicolous species of gecarcinucid, Arachnothelphusa sarang Grinang & Ng, 2021, is present. Bukit Sarang is an isolated limestone outcrop with a complex of small caves, most of which probably have subterranean interconnections, and is part of the Tatau river basin in central Sarawak. The type specimen was obtained in moist areas several hundred meters from the cave entrance (RB Stuebing pers. comm.). Although more surveys in and around the Bukit Sarang were conducted in 2006 and more specimens of A. sarang were collected ( Grinang and Ng 2021), no other specimens of Geosesarma were forthcoming.
Geosesarma sodalis sp. nov., however, does not have prominently elongated legs or reduced eyes typical of true troglobitic taxa, and must be treated as troglophile. It is probably more widespread outside the cave habitat. The site it was collected from is several hundred metres from the cave entrance and there was no light at all. The sympatric Arachnothelphusa sarang possesses some cave-dwelling characters-there is hardly any pigmentation on the body and legs and the pereopods are elongated, but the eyes are not reduced with the cornea still distinct, with Grinang and Ng (2021) treating it only as a troglophilic species.
No Geosesarma species had previously been recorded from caves, although one sesarmid genus Karstarma Davie & Ng, 2007, is known to live in or closely associated with limestone caves. Karstarma species are widely distributed in the Indo-West Pacific, with 18 recognised species (see Wowor and Ng 2018; Poupin et al. 2018; Ng 2020). Wowor and Ng (2018) recognised three species-groups in Karstarma and discussed the affinities of one of these groups with Geosesarma . They commented that the characters of some Karstarma species (e.g, K. microphthalmus (Naruse & Ng, 2007) and K. malang Wowor & Ng, 2018) are close to Geosesarma . Until the present discovery of G. sodalis sp. nov., no species of Geosesarma has previously been found in caves. Geosesarma sodalis sp. nov., however, has none of the morphological features associated with a cavernicolous lifestyle, e.g., reduced eyes and/or cornea and elongated pereopods. In any case, G. sodalis sp. nov. differs markedly from the group of Karstarma species highlighted by Wowor and Ng (2018) in its quadrate carapace, proportionately shorter ambulatory legs, and stouter G1, as well as its well-developed eyes with the large pigmented cornea.
Another species of sesarmid which was originally desrribed from near the entrance of a cave in Myanmar, Pseudosesarma brehieri Ng, 2018, is now known to normally live in mangrove habitats ( Ng 2018; Schubart and Ng 2020).
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