Geosesarma faustum, Ng, 2017

Ng, Peter K. L., 2017, On the identities of the highland vampire crabs, Geosesarma foxi (Kemp, 1918) and G. serenei Ng, 1986, with description of a new phytotelmic species from Penang, Peninsular Malaysia (Crustacea: Decapoda: Brachyura: Sesarmidae), Raffles Bulletin of Zoology 65, pp. 226-242 : 235-240

Geosesarma faustum n. sp.

( Figs. 8–12 )

Material examined. Holotype: male (10.6 × 10.5 mm) ( ZRC 2016.617 ), Penang Hill , near Bellevue Hotel, Penang, 800 m, Peninsular Malaysia, inside introduced bromeliad Neoregalia compacta ( Bromeliaceae ), coll. J. Tan & Z.Y. Chan, June 2014 . Paratypes: 2 males (10.6 × 10.5 mm, 8.9 × 8.7 mm), 4 females (12.0 × 11.5 mm, 11.1 × 10.7 mm, 11.0 × 10.7 mm, 10.6 × 10.6 mm), 2 ovigerous females (10.6 × 10.4 mm, 9.5 × 9.4 mm) ( ZRC 2014.340 ), same data as holotype ; 5 males (10.2 × 10.1 mm, 10.0 × 10.3 mm, 8.6 × 8.4 mm, 8.3 × 8.2 mm, 6.2 × 6.0 mm), 2 females (10.8 × 10.9 mm, 8.6 × 8.6 mm), 1 ovigerous female (9.2 × 9.3 mm), 1 young female (6.8 × 6.5 mm) ( ZRC 2016.0599 ), in various bromeliads and Pandanus growing in shaded gardens at summit of Penang Hill , mostly near Bellevue Hotel, Penang, ca. 850 m, Peninsular Malaysia, coll. P.K.L. Ng & P.Y.C. Ng, 20 December 2016 .

Diagnosis. Carapace quadrate, slightly wider than long or subequal, adult width to length ratio 0.97–1.04, lateral margins parallel ( Figs. 9A–C , 10); dorsal surface with regions just visible, anterior regions with small rounded granules on gastric regions ( Fig. 9B–D ); front distinctly deflexed, frontal lobes broad, usually with truncate margins in dorsal view; postfrontal, postorbital cristae sharp, distinct ( Figs. 9A–C , 10); external orbital tooth acutely triangular, directed obliquely laterally, outer margin gently convex, tip not extending beyond lateral margin; second lateral tooth low, barely discernible from rest of margin, often fused with rest of margin ( Figs. 9B, C , 10). Merus of third maxilliped subovate, shorter than ischium; exopod slender with no trace of flagellum ( Fig. 12A ). Outer surface of palm of adult male covered with small rounded granules and striae; inner surface granulated but without transverse ridge; dorsal margin of dactylus with 7–9 low, non-chitinous tubercles on proximal half ( Figs. 9A , 10, 11D). Ambulatory legs with long, slender merus, with sharp subdistal spine on dorsal margin, surfaces gently rugose ( Figs. 9A , 10). Male pleon broadly triangular; somite 6 very wide, with convex lateral margins; telson relatively triangular, not recessed into distal margin of somite 6 ( Figs. 11A–C, E ). G1 slender; outer margin of subdistal part of subterminal segment (in ventral view) with sloping, subangular shelf-like area ( Fig. 12B–E ), distal chitinous part conspicuously elongated, distal part gently curved, tip spatuliform ( Figs. 11F , 12B–G ).

Females. Females resemble males in all non-sexual characters, with the chelae equal, relatively slenderer and less inflated ( Figs. 8H , 10B). The pleon is ovate, covering most of the thoracic sternum, with the telson broadly triangular with convex lateral margins and distinctly inserted into the distal margin of somite 6 ( Fig. 11G ). The vulvae on thoracic sternite 6 are large, positioned closer to suture with sternite 5, with an operculum and a large truncate vulvar process which arches over the opening ( Fig. 11H ). The ovigerous females (10.6 × 10.4 mm, 9.5 × 9.4 mm, ZRC 2014.340) had large subovate eggs, each measuring about 1.5 mm in diameter ( Fig. 8D ).

Variation. The margins of the frontal lobes in G. faustum is usually subtruncate, but in several specimens, it appears more convex (Fig. 10A). As in G. foxi , the carapace shape varies slightly from just longer than broad to broader than long. The carapaces of many of the adult females and young males appear to be slightly more trapezoidal with the lateral margins gently diverging ( Figs. 8H , 9C ).

Colour. The colour and pattern of G. faustum n. sp. is very similar to G. foxi . The anterior half of the carapace, chelipeds, suborbital, subhepatic and pterygostomial regions are usually pale yellow to light orange ( Fig. 8 ), never red. The posterior half of the carapace and ambulatory legs vary from brown to purplish black, with numerous small white or light blue spots ( Fig. 8 ).

Etymology. The species name is derived from the Latin for fortunate and lucky; alluding to the circumstances leading to the discovery of the new species.

Taxonomic remarks. Kemp (1918: 240) reported on a “ Sesarma sp. ” from an altitude of about 370 m on Penang Hill. Tweedie (1940) obtained more specimens from Penang Hill (no altitude provided), named the species Sesarma penangensis , and referred Kemp’s (1918) record to his new taxon. From Kemp’s (1918) description of his specimens, the author has little doubt that Tweedie is correct, and his specimens are not conspecific with what is here described as G. faustum . Geosesarma faustum is one of the highland Geosesarma species (see earlier; Ng, 1988), while G. penangense is a congener that is generally found at relatively lower altitudes; it is easily distinguished from G. faustum by its distinctly broader than long carapace, conspicuously shorter and stouter ambulatory legs, the exopod of the third maxilliped possessing a long flagellum and the G1 is proportionately stouter with short, spade-like chitinous distal part (cf. Ng, 1988: fig. 58A, C–E).

Geosesarma foxi and G. faustum n. sp. share a similar colour pattern, with the anterior half of the carapace and chelipeds bright yellow or orange, with the dark brown to almost black posterior half of the carapace and ambulatory legs covered with numerous small white dots. The same appears to be the case for G. serenei , with the more recent specimens showing traces of the small dots on the ambulatory legs.

While G. foxi s. str. is very similar to G. faustum , adults of G. faustum can easily be distinguished by the second lateral tooth on the carapace being poorly developed or almost undiscernible ( Figs. 9B, C , 10) (distinct in G. foxi , Figs. 1A , 3B, C , 4 ); the male pleonal somite 6 is more subtruncate in shape ( Fig. 11A–C, E ) (margins distinctly more convex in G. foxi , Fig. 5A–C ); the telson is more triangular in shape ( Fig. 11A ) (more semicircular in G. foxi , Fig. 5A ); the outer margin of the subdistal part of the subterminal segment is gently sloping ( Fig. 12B–E ) (area forms a distinct angular shelf-like structure in G. foxi , Fig. 7B–E ); and the chitinous distal part of the G1 is proportionately longer ( Fig. 12B–E ) (proportionately shorter in G. foxi , Fig. 7B–E ). In addition, the external orbital tooth is usually relatively more acutely Fig. 10. Geosesarma faustum n. sp., overall dorsal view. A, triangular ( Figs. 9A–C , 10) (more broadly triangular in G. paratype male (10.6 × 10.5 mm) (ZRC 2014.340), Penang Hill, foxi , Figs. 3A–C , 4 ). The colour in life of the anterior half Penang; B, paratype female (12.0 × 11.5 mm) (ZRC 2014.340), of the carapace and chelipeds of adult G. foxi s. str. is deep Penang Hill, Penang. orange ( Fig. 2A–D ), sometimes becoming almost red ( Fig. 2F, G ). In contrast, the live colour of G. faustum tends to Sympatric taxa. A second species of Geosesarma , G. be pale yellow ( Fig. 8A–D ) to light orange ( Fig. 8E–H ). penangense ( Tweedie, 1940) is present on Penang Hill, Although colour will probably vary slightly in a species, but has not been found higher than 370 m asl (see above). the good series of specimens of both species indicate that Living in the waterfalls and rocky streams is the fully aquatic the orange of G. foxi generally tends to be darker. potamid Stoliczia stoliczkana ( Wood-Mason, 1871) , but this species is not known from the summit (see Ng, 1992). Compared to G. serenei , the external orbital tooth of adult G. faustum is relatively more acutely triangular ( Figs. 9A–C , 10) (more broadly triangular in G. serenei , Fig. 6A, B, E , GENERAL DISCUSSION F); the second lateral tooth on the carapace of G. faustum n. sp. is poorly developed or almost undiscernible ( Figs. 9B, C , Geosesarma foxi , G. serenei and G. faustum are high altitude 10) (more distinct in G. serenei , Fig. 6A, B, E, F ); the male species, occurring in montane habitats higher than 700 m pleonal somite 6 is more subtruncate in shape ( Figs. 11A–C , asl. With regards to G. foxi, Kemp (1918: 240) recorded E) (relatively less broad in G. serenei , Fig. 6C ); the telson that the “specimens obtained by Mr. Buxton, the types of is more triangular in shape ( Fig. 11A ) (more semicircular the species, were found on Gunong Raya in Langkawi I, in G. serenei , Fig. 6C ); and the chitinous distal part of the at a height of 2000 ft. They were collected in moist places G1 is proportionately longer ( Fig. 12B–E ) (proportionately under stones or rotten wood at some distance from any shorter in G. serenei , Fig. 7I, J ). The live colours of G. stream.” He also noted that “It appears probable that in serenei are not known. these places the Sesarma have been able to adopt a strictly terrestrial mode of life and to ascend to considerable altitudes In its carapace shape, elongated ambulatory legs and color owing to the damp climate that prevails...” ( Kemp, 1918: pattern, G. faustum bears a close resemblance to what has been 238). The recent specimens of G. foxi were all found near reported in the aquarium trade as “ Geosesarma krathing ” (see the summit of Gunung Raya: “they were collected in the Rademacher & Mengedoht, 2011). This material supposedly densely forested area near the top of the Gunung Raya came from the type locality, Krathing Waterfalls in Thailand, hiking trail, at roughly 700 m plus asl. Geosesarma foxi is but considering the general unreliability of aquarium records, nocturnal, and the majority of specimens were collected it is quite possible that the specimens were from Penang or late at night (after 10 pm) foraging among the plants, often even Langkawi instead. While the colour (yellow) and pattern ferns, along the side of the trail. The area is a considerable (the anterior half of the carapace and chelipeds are yellow) distance from any stream or permanent water source, but are very similar, these aquarium specimens do not appear almost always moist due to cool temperatures of the high to have the posterior part of the carapace and legs covered altitude and thick mist that blankets the area in the early with fine spots like in true G. faustum ( Fig. 8 ). morning and night. During the day, this species probably takes refuge in the moist leaf litter or in phytotelms such as between the leaves of Pandanus spp. ” (P.Y.C. Ng, personal communication). Not much is known about the ecology of G. serenei , with the types collected at the summit of Bukit Larut, over 1000 m asl. As far as is known, they were found in the forest, with the recent material (ZRC 2003.64) collected at night.

The discovery of G. faustum in Penang is interesting because the species has never been reported in earlier publications despite the fact that Penang had been a major British bastion since 1786 and Penang Hill, the highest point on the island, has been inhabited for most of that time. This may not be surprising considering the biology of G. foxi and G. serenei . They are very cryptic species, hiding in the dense forest or among vegetation during the day, coming out to forage only late at night. Phytotelms are probably one of their major habitats or foraging sites. In natural forests or urban habitats where water may be scarcer, the crabs are rarely seen. Even for G. foxi , they have only been found recently, and not in large numbers. Since 2010, Penang Hill, especially the summit area, has been developed with the addition of new tourist facilities, hotels and natural attractions. These include many ecogardens and newly planted areas. Many areas are heavily planted with non-native bromeliads and Pandanus . The density of bromeliad plantings in and around the hotel area as well as the gardens means a new habitat has been created for species of Geosesarma , allowing them to flourish in good numbers so much so that they are now far more accessible for scientists to study. In the natural ecosystem, they are almost certainly more widely dispersed due to the more scattered distribution of suitable plants and the density of the vegetation on the forest floor.

Geosesarma faustum was observed to hide between the leaves of the bromeliads and Pandanus , scurrying into the water if disturbed ( Fig. 8A, B ). They were common during the day, especially in more shaded areas, and when there was cloud cover with light rain. Several females with eggs were seen, and numerous very small crabs were also seen around the plants, suggesting the crabs are breeding in the phytotelm. The large size of the eggs of all three species indicates that they practice direct development but it is not known if they carry the young crabs under their pleon, on the back of their carapaces (see Ng & Tan, 1995), or perhaps release the newly hatched crabs in the waters of the phytotelms.

Several species of Geosesarma are known to use various phytotelmata. Geosesarma malayanum Ng & Lim , in Ng, 1986, has been found in the cups of pitcher plants at high altitudes ( Ng & Lim, 1987), while G. peraccae ( Nobili, 1903) and G. nemesis Ng, 1986 , from Singapore have been known to also frequent or use pitcher plants (notably Nepenthes ampullaria ) ( Tan & Ng, 2008; Ng & Court, 2010). In Sarawak (and Brunei), G. gracillimum (De Man, 1902) has been found in pitcher plants (unpublished data).

As to their conservation status, Ng & Yeo (2007: 115) listed G. foxi as “endangered”, while G. serenei was regarded as “critically endangered”; the authors noting that the small known distribution range and possible threats to the forests were problems. While the present study has managed to get more specimens of G. foxi for study, the various environmental threats facing this species have not been reduced. In fact, the threats may get worse in the years ahead as more parts of Gunung Raya (and Bukit Larut for G. serenei ) are opened for increasing numbers of tourists. The same may be true for G. faustum , although the prolific planting of plants like bromeliads on the summit of Penang Hill has clearly helped the species, at least for the moment. Another potential problem is the aquarium trade. Ng et al. (2015: 12) noted that over-collecting is a serious threat for a species if it becomes popular in the trade as catching animals from the wild is not a sustainable practice. The ease by which Geosesarma crabs are kept and their often striking colours in life and habits, have made them much sought after terrarium subjects (see Rademacher & Mengedoht, 2011; Ng et al., 2015). The conservation status of primarily or wholly freshwater sesarmids like Geosesarma , however, have not been analysed following IUCN Red List guidelines, as had been done for primary freshwater crabs (see Cumberlidge et al., 2009).

Figures

Fig. 8. Geosesarma faustum n. sp., colour in life, Penang Hill, Penang. A, B, specimens photographed in bromeliad in situ, part of type species; C, holotype male (10.6 × 10.5 mm) (ZRC 2016.617); D, paratype ovigerous female (10.6 × 10.4 mm) (ZRC 2014.340); E–G, paratype male (10.2 × 10.1 mm) (ZRC 2016.0599); H, paratype female (10.8 × 10.9 mm) (ZRC 2016.0599). Photo credits: A–D, Ji Tan; E–H, Paul Y. C. Ng.

Fig. 9. Geosesarma faustum n. sp. A, B, D, holotype male (10.6 × 10.5 mm) (ZRC 2016.617), Penang Hill, Penang; C, paratype female (12.0 × 11.5 mm) (ZRC 2014.340), Penang Hill, Penang. A, overall dorsal view; B, C, dorsal view of carapace; D, frontal view of cephalothorax.

Fig. 11. Geosesarma faustum n. sp. A–D, holotype male (10.6 × 10.5 mm) (ZRC 2016.617); E, F, paratype male (10.6 × 10.5 mm) (ZRC 2014.340); G, H, paratype female (12.0 × 11.5 mm) (ZRC 2014.340). All specimens from Penang Hill, Penang. A, anterior thoracic sternum, telson and pleonal somites 5 and 6; B, anterior thoracic sternum, telson and pleonal somites 3–6; C, posterior thoracic sternum, telson and pleonal somites 2–6; D, outer view of right chela; E, posterior thoracic sternum, telson and pleonal somites 3–6; F, male sternopleonal cavity showing G1s; G, female pleon; H, female sternopleonal cavity showing vulvae.

Fig. 12. A–H, G. faustum n. sp., holotype male (10.6 × 10.5 mm) (ZRC 2016.617), Penang Hill, Penang. A, left third maxilliped (mostly denuded); B, left G1 (ventral view); C, left G1 (dorsal view); D, distal part of left G1 (ventral view); E, distal part of left G1 (dorsal view); F, distal part of left G1 (outer lateral view); G, distal part of left G1 (mesial view); H, left G2. Scales = 0.5 mm.

Fig. 1. Geosesarma foxi (Kemp, 1918), lectotype male (9.8 × 9.8 mm), Gunung Raya, Langkawi (after Kemp, 1918: figs. 3, 4). A, overall dorsal view; B, outer view of left chela.

Fig. 3. Geosesarma foxi (Kemp, 1918), male (11.4 × 11.0 mm) (ZRC 2016.0598), Gunung Raya, Langkawi. A, overall dorsal view; B, C, dorsal view of carapace (viewed from slightly different angles); D, frontal view of cephalothorax.

Fig. 4. Geosesarma foxi (Kemp, 1918). A, C, male (9.9 × 10.0 mm) (ZRC 2016.618); B, D, female (10.8 × 10.9 mm) (ZRC 2016.618). Both specimens from Gunung Raya, Langkawi. A, B, overall dorsal view; C, D, dorsal view of carapace.

Fig. 5. Geosesarma foxi (Kemp, 1918). A–D, male (11.4 × 11.0 mm) (ZRC 2016.0598); E, F, female (10.8 × 10.9 mm) (ZRC 2016.618). Both specimens from Gunung Raya, Langkawi. A, anterior thoracic sternum, telson and pleonal somites 4–6; B, anterior thoracic sternum, telson and pleonal somites 3–6; C, posterior thoracic sternum, telson and pleonal somites 2–6; D, outer view of right chela; E, female pleon; F, female sternopleonal cavity showing vulvae.

Fig. 7. A–H, Geosesarma foxi (Kemp, 1918), male (11.4 × 11.0 mm) (2016.0598), Gunung Raya, Langkawi; I–M, G. serenei Ng, 1986, holotype male (8.3 × 8.2 mm) (ZRC 1964.9.8.1), Bukit Larut, Perak; N–P, G. serenei Ng, 1986, young male (7.0 × 6.9 mm) (ZRC 2003.64), Bukit Larut. A, left third maxilliped (mostly denuded); B, I, N, left G1 (ventral view); C, J, left G1 (dorsal view); D, distal part of left G1 (ventral view); E, distal part of left G1 (dorsal view); F, K, O, distal part of left G1 (outer lateral view); G, L, P, distal part of left G1 (mesial view); H, M, left G2. Scales = 0.5 mm.

Fig. 2. Geosesarma foxi (Kemp, 1918), colour in life, Gunung Raya, Langkawi. A, B, male (10.9 × 10.9 mm) (ZRC 2016.618); C, male (9.9 × 10.0 mm) (ZRC 2016.618); D, female (10.8 × 10.9 mm) (ZRC 2016.618); E, juvenile male (8.0 × 7.9 mm) (ZRC 2016.618); F, male (11.5 × 11.4 mm) (ZRC 2016.619); G, probably male (9.6 × 9.7 mm) (ZRC 2016.619). Photo credits: A–E, Paul Y.C. Ng; F, G, J.-J. Li.

Fig. 6. Geosesarma serenei Ng, 1986. A–D, holotype male (8.3 × 8.2 mm) (ZRC 1964.9.8.1); E, F, young male (7.0 × 6.9 mm) (ZRC 2003.64); G, H, paratype ovigerous female (10.4 × 9.7 mm) (ZRC 1964.9.8.2). All specimens from Bukit Larut, Perak. A, E, overall dorsal view; B, F, dorsal view of carapace; C, male pleon; D, outer view of left chela; G, female pleon; H, female sternopleonal cavity showing vulvae.