Geosesarma larsi Ng & Grinang 2018, n. sp.
Creators: name: Ng, Peter K. L.
name: Grinang, Jongkar
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Geosesarma
Geosesarma larsi

description: Geosesarma larsi n. sp.
(Figs. 1–4)
Material examined. Holotype: male (13.6 × 13.4 mm) (ZRC 2017.1296), Gunung Ampungan, 600 m asl, Serian Division, Sarawak, at night, coll. J. Grinang & L. Fehlandt, 21 June 2017. Paratypes: 1 female (14.5 × 13.5 mm), 1 ex-ovigerous female (12.6 × 12.5 mm) (ZRC 2017.1297), 3 males (largest 13.4 × 13.0 mm) (SBC), 1 female (14.1 × 12.8 mm) (SBC), 3 females with young crabs (largest 12.7 × 12.1 mm), same data as holotype, male (13.5 × 12.5 mm (SBC), 1 female (15.0 × 15.0 mm) (SBC), Gunung Ampungan, 600 m asl, Serian Division, Sarawak, night, coll. L. Fehlandt, 22 December 2016.
Diagnosis of male. Carapace almost square, width to length ratio 1.01–1.07, lateral margins gently sinuous, subparallel (Fig. 2A, C); dorsal surface with well-defined regions, anterior regions covered with small rounded or flattened granules (Fig. 2C); front deflexed, with 2 broad subtruncate lobes, separated by shallow median concavity; postfrontal, protogastric lobe prominent, very sharp, strong (Fig. 2C, D); external orbital tooth triangular, outer margins curving anteriorly, tooth directed obliquely laterally, clearly extending beyond lateral margin (Fig. 2 A–C). Merus of third maxilliped subovate, subequal in length to ischium; exopod slender, without trace of flagellum (Fig. 5A). Outer surface of palm of adult male covered with small rounded granules; inner surface with low median ridge; dorsal margin of dactylus with 11 or 12 tubercles (distal one smallest), each with corneous tip (Fig. 3 A–C). Ambulatory legs with relatively slender merus, with sharp subdistal spine on dorsal margin, surfaces slightly rugose (Figs. 1A, B, 3 D–F). Male pleon triangular; somite 6 relatively broad, with gently convex lateral margins; telson triangular with convex lateral margins (Fig. 4 A–C). G1 stout, subdistal part of outer margin (ventral view) with distinct sloping hump-like structure; corneous distal part elongate from lateral view, bent at angle of ca. 45° from longitudinal axis, spatuliform from marginal view, with small median cleft (Fig. 5 B– G).
Females. In larger females, the carapace shape is relatively more trapezoidal, with the lateral margins more divergent towards posterior carapace margin (Fig. 2B). The female pleon is almost round, covering most of thoracic sternum (Fig. 4D), and the vulva is ovate, positioned on the anterior half of sternite 6 with an opercular cover (Fig. 4E).
Live colouration. Adult G. larsi n. sp. (Fig. 1) have the anterior half of the carapace, ambulatory meri, and the merus, carpus and palm of the cheliped purple to purplish-red; with the posterior carapace surface pink to reddishwhite, the ambulatory prodi and dactyli orange to red, the fingers of the chela orange. The ventral surfaces are a pale purplish-red to pink (Fig. 1D). The eyes are yellow to reddish-yellow (Fig. A). The eggs are reddish-orange (Fig. 1F).
Etymology. The species is named after Lars Fehlandt who first observed this species and helped the authors get specimens.
Remarks. The purplish-red colour of Geosesarma larsi n. sp. is not known in any other congener in Borneo. Morphologically, G. larsi n. sp. belongs to a group in which the exopod of the third maxilliped has no trace of a flagellum, the G1is relatively stout and short, and whose members often occur at higher altitudes (see Ng 2015, 2017).
The western part of Sarawak has two other species, G. sarawakense (Serène, 1968) and G. bau Ng & Grinang, 2004, both from lowlands. Geosesarma larsi n. sp. is immediately separated from G. sarawakense by the absence of a flagellum on the third maxilliped exopod. Geosesarma larsi n. sp. more closely resembles G. bau (from Bau and Kuching areas) in the squarish carapace shape, obliquely directed external orbital teeth and absence of a flagellum on the exopod of the third maxilliped, but can be distinguished by its more granular lateral carapace surfaces (Fig. 2 A–C) (versus smoother lateral carapace surfaces; Ng & Grinang 2004: figs. 8, 9A, B); proportionately stouter and shorter ambulatory meri (Figs. 2A, B, 3 D–F) (versus proportionately more slender and longer ambulatory meri; Ng & Grinang 2004: fig. 8); and taxonomically significant, G1 being relatively short and stout with the distal corneous process bent at angle of 45° from the longitudinal axis (Fig. 5B, C, D, F) (versus G1 slender and long, with corneous distal part bent at an angle of 30°; Ng & Grinang 2004: fig. 9D, F).
In its squarish male carapace, obliquely directed external orbital teeth, absence of a flagellum on the exopod of the third maxilliped and stout G1 with the corneous part directed at about 45°, Geosesarma larsi n. sp. most closely resembles G. ambawang Ng, 2015, from Pontianak in West Kalimantan in Indonesian Borneo. Geosesarma larsi n. sp., however, can be distinguished from G. ambawang by the carapace surfaces with proportionately much fewer granules (Fig. 2C) (versus anterior part of the carapace being strongly granulated on the frontal, gastric and branchial surfaces, with prominent rounded granules in G. ambawang; Ng 2015: fig. 8B); the male pleonal somite 6 is proportionately broader (Fig. 4A, B) (versus proportionately more narrow in G. ambawang; Ng 2015: fig. 8D), and the G1 is relatively shorter and stouter (Fig. 5B, C) (versus relatively more slender in G. ambawang; Ng 2015: fig. 9D, E). The colour of G. larsi n. sp. is purplish-red on the anterior half of the carapace, ambulatory meri and chelipeds (Fig. 1), whereas G. ambawang is brown to reddish-brown on the anterior half of the carapace with the chelipeds and ambulatory legs reddish-brown to red (Ng 2015: fig. 10). The morphology of the carapace in larger females of G. larsi n. sp. (Fig. 2B) has also been reported for montane species like G. foxi (Kemp, 1918) from Pulau Langkawi in Peninsular Malaysia (Ng 2017).
From G. gracillimum (De Man, 1902) which occurs in lowlands in eastern Sarawak and Brunei, G. larsi n. sp. can be easily be distinguished by its less quadrate carapace, proportionately stouter and shorter ambulatory legs, and relatively stouter G1 (Figs. 2 A–C, 3D–F, 5B–G) (cf. Ng 1995: fig. 13B–E; Ng 2015: fig. 14A, B).
Ecological notes. Geosesarma larsi n. sp. lives in shallow soil burrows on a steep slope under shaded canopy at relatively higher altitudes. Individuals were observed foraging at night on the ground among the bases of ferns. They were also found inside the phytotelms formed by the water-filled bases of the ferns.
From habitats just lower down Gunung Ampungan, Grinang & Ng (2015) described a new species of semiterrestrial gecarcinucid crab, Lepidothelphusa loi, from around 500 m asl. The aquatic potamid Ibanum pilimanus Ng & Grinang, 2004, is also present, as is a potentially new species of gecarcinucid (genus Bakousa Ng, 1995), which was also collected with L. loi. At this site, however, no other species of Geosesarma was collected or observed.
Conservation notes. From the conservation perspective, G. larsi n. sp. is a species of concern because it appears to be confined to a relatively small highland area. The habitat is not protected and has a high chance of being degraded if adjacent agricultural activities such as oil palm plantations and orchards are expanded. The area will need to be more thoroughly surveyed to see if the species is more widespread.
description: Published as part of Ng, Peter K. L. & Grinang, Jongkar, 2018, A new species of highland vampire crab (Crustacea: Brachyura: Sesarmidae: Geosesarma) from Serian, Sarawak, pp. 569-575 in Zootaxa 4508 (4) on pages 570-573, DOI: 10.11646/zootaxa.4508.4.5, http://zenodo.org/record/2607544