Circulium vitatum ( Ng and Davie, 2011 ) Naruse & Ng, 2020

Naruse, Tohru & Ng, Peter K. L., 2020, Revision of the sesarmid crab genera Labuanium Serène and Soh, 1970, Scandarma Schubart, Liu and Cuesta, 2003 and Namlacium Serène and Soh, 1970 (Crustacea: Decapoda: Brachyura: Sesarmidae), with descriptions of four new genera and two new species, Journal of Natural History (J. Nat. Hist.) 54 (7 - 8), pp. 445-532 : 463-465

Circulium vitatum ( Ng and Davie, 2011) , comb. nov.

( Figure 7 (a,b))

Sesarma oceanicum: Alcock 1900, p. 423 ; George 1978, p. 14.

Sesarma (Episesarma) rotundata papuo-malesiaca: Nobili 1900, p. 510 (part).

Sesarma (Sesarma) rotundata: Tesch 1917, p. 193 (part).

Labuanium rotundatum: Serène and Soh 1970, p. 401 (part); Hicks et al. 1984, p. 64; Davie 2002, p. 221 (part); Ng and Liu 2003, p. 614 (part); Ng et al. 2008a, p. 221 (part).

Labuanium vitatum Ng and Davie, 2011, p. 37 , figs 1, 2A, 3A, 4A, 5A, B, 6A, 7, 8, 10A–G [type locality: Christmas Island].

Material examined

Holotype. WAM C13977, male, 35.3 × 34.7 mm, 60 m above beach , on tree trunk, on track to West White Beach , Christmas Island, coll. D. Merton, 11 February 1978.

Paratype. WAM 19380, 1 male, 39.2 × 39.2 mm, The Dales , Christmas Island, coll. H . Yorkston, ca. January 1989.

Others. RMNH 1989 , male, 24.8 × 25.5 mm, Nias , Indonesia, coll. E.E.W.G. Schröder, 1908; ZRC 2002.0099 , 1 male, 33.7 × 34.9 mm, Cuthbert Bay , Andamans, India, coll. P. Biswas, 2001; ZRC 2014.0283 , 3 males, 17.8 × 17.8–22.6 × 22.8 mm, 1 juv., 9.7 × 10.0 mm, Ambon, Indonesia, coll. H.H. Tan, 12–20 August 2012.

Diagnosis

Two pairs of postfrontal lobes present, lateral lobes exceeding mesial lobes anteriorly, anterior edge of lobes far from frontal margin in dorsal view. Epistome posterior margin with 3 low lobes, lateral lobes terminally directed ventrally, median lobe terminally directed anteroventrally. Chela outer surface covered with closely arranged small granules; upper surface with incomplete row of small granules. G1 stout, relatively long, straight proximally, distally bent about 45° against main axis; distal beak-like and corneous part relatively short, narrow. Vulva not known.

Colouration

In life, carapace variable from yellowish brown to purplish with beige lateral margins, pale purple legs, bright purple palm and red fingers ( Ng and Davie 2011).

Distribution

Eastern Indian Ocean to Indonesia: Christmas Island ( Hicks et al. 1984) [type locality]; Nicobar Island ( Alcock 1900), Nias ( Nobili 1899, 1900), west Java ( Tesch 1917), Ambon (present study).

Remarks

Ng and Davie (2011) described Circulium vitatum from islands of the north-eastern Indian Ocean. Circulium vitatum is morphologically similar to C. papuomalesiacum known from Western New Guinea [type locality: Cenderawasih Bay, Irian Jaya], Caroline Islands and Solomon Islands ( Ng and Davie 2011), but the former is differentiated from the latter as the G1 is proportionately shorter and the corneous distal part is shorter and gently sinuous ( Ng and Davie 2011, fig. 10A, B), whereas that of C. papuomalesiacum is relatively longer and the corneous distal part is proportionately longer and almost straight ( Ng and Davie 2011, fig. 10H, I). We have examined Circulium specimens from Ambon, only some 100 km away from New Guinea Island ( Figure 7 (a,b). Interestingly, those specimens from Ambon have proportionately shorter G1 with shorter and gently sinuous corneous distal part, which are diagnostic of C. vitatum . They agree with C. vitatum also in other diagnostic characters. Despite the wide geographic distance from the north-eastern Indian Ocean, the specimens from Ambon are here referred to as C. vitatum for the time being.

Ecological note

Labuanium vitattum is also an arboreal species and has been collected usually at the base of trees in relatively close proximity to the sea ( Ng and Davie 2011). This species grows up to 40 mm in carapace width and spawns about the time of the full moon between November and April ( Hicks et al. 1984, p. 64). The species has also been observed among leaves of palms (M. Orchard, personal communication). Females with eggs walk across the sand to release their larvae during the beginning of the year, several weeks after the mass spawning event of the island’s famous red crabs ( Gecarcinidae : Gecarcoidea natalis (Pocock, 1889)) (Liu Hung-Chang, personal communication).

Figures

Figure 7. a, b, Circulium vitatum (Ng and Davie, 2011), ZRC 2014.0283 (Ambon, Indonesia) showing colouration in life; c, Scandarma gracilipes (H. Milne Edwards 1853), ZRC 2018.0056, male, 12.8 × 13.7 mm (Vanuatu), showing colouration in life; d, Scandarma malagasy sp. nov., ZRC 2010.0303, female, 20.5 × 22.0 mm (Madagasacar), showing colouration in preservative (about 6 years and 8 months). Photographed by Tan Heok Hui (a, b) and P.K.L. Ng (c).