Scandarma malagasy, 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 : 493-496

Scandarma malagasy sp. nov.

( Figures 7 (d), 26)

Sesarma Finni : Lenz 1910, p. 560.

Sesarma (Sesarma) gracilipes: Crosnier 1965, p. 59 , figs 80, 87, 95, pl. 3, fig. 2; Cumberlidge et al. 2005, p. 304.

Material examined

Holotype. MNHN-B11025 , male, 17.0 × 18.4 mm, Ivontaka , Cȏte est de Madagascar, coll. Voeltzkow, 1903–1905.

Others. ZRC 2010.0303 , 1 female, 20.5 × 22.0, Mosoala Peninsula, Madagasacar, coll. W. Emmerson, June 2005 .

Diagnosis

Carapace squarish, external orbital angle blunt, lateral margins almost parallel; 2 pairs of postfrontal lobes present, all lobes aligned anteriorly; anterior margins of all lobes far from frontal margin in dorsal view ( Figure 26 (a)). Chelae stout ( Crosnier 1965, pl. 3, fig. 2); palm of male chela ( Figure 26 (b,c)) swollen; outer surface granulated, with weak protuberance on proximal part of smooth sloping area around bases of fingers; upper surface ( Figure 24 (d); Crosnier 1965, fig. 95) with several short rows of small granules, these rows not longitudinally transverse. Immovable finger straight, occlusal margin lacking marked proximal elevation, lined with small teeth on proximal two-fifths, 1 large tooth submedially, followed distally by 3 small teeth, 1 large tooth on distal fifth, 1 smaller tooth subdistally; lower margin of immovable finger with irregular row of small teeth. Movable finger ( Figure 26 (c)) gently curved, occlusal margin lined with 2 large teeth flanking 1 small tooth, followed distally by small teeth, and 1 subdistal tooth; inner side of upper surface of movable finger with sparsely aligned small granules. Subdistal tooth of movable finger ( Figure 26 (c)) fitting between 2 subdistal teeth of immovable finger when closed. Male pleonal somite 3 widest, somite 4 abruptly narrowed distally, lateral margins of somites 3–5 clearly concave; telson rounded distally, slightly longer than somite 6 ( Figure 26 (b); Crosnier 1965, fig. 80). G1 ( Crosnier 1965, fig. 87) short, almost straight, stout, narrowed medially, distal end with laterally directed wide corneous process. Vulvae adjacent to thoracic sternal suture 5/6 on distal half of sternite 6, oblique ellipsoidal, rimmed proximally; sternal vulval cover developed from posterolateral margin, covering vulva, except for gap on mesial fifth, cover produced ventromesially as earlobe-like structure.

Variations

In small females (e.g. CW 11 mm), the anterior margin of the front is almost straight; the postfrontal lobes are aligned anteriorly, the mesial lobe are as wide as the lateral lobe; and there are 2 discernible epibranchial teeth on the anterolateral margin of the carapace ( Lenz 1910).

Colouration

In life, carapace dark brown to purple, ventral thoracic surface light brown; upper surface of cheliped merus, carpus and propodus bight orange, fingers cream; P2–5 uniformly light brown ( Cumberlidge et al. 2005). Cephalothorax dark reddish brown with a few irregularly scattered lighter spots; legs lighter; chelae reddish yellow ( Lenz 1910).

Distribution

Madagascar [Ivontaka (type locality), Fénérive, Ste. Marie and Tampolo] ( Crosnier 1965; Cumberlidge et al. 2005).

Etymology

Malagasy is the name used for people and items derived from Madagascar; and it is here used as the Latin name for the present new species. The name is used as a noun in apposition.

Remarks

Alfred Voeltzkow collected 1 male and several female specimens of what can be referred to as Sesarma finni from Fénérive and Ste. Marie, Madagascar, during his trip in 1903–1905 (see Lenz 1910, p. 539). Lenz (1910) compared these specimens with the original description of Sc. finni ( Alcock, 1900; Alcock and McArdle 1903, pl. 66, fig. 1). He also examined small Madagascar specimens (up to CW 11 mm, see Variation above) to consider the small size of the holotype of Sc. finni (CW 11 mm) and concluded that they are conspecific. However, Lenz (1910) noted that the Madagascar specimens have the postfrontal lobes of the carapace almost the same width in both lateral and mesial ones, whereas the mesial lobes are about 2 times wider than the lateral lobes in the holotype of Sc. finni ( Figure 25 (a)). Moreover, Lenz (1910, p. 561) mentioned that the ambulatory legs of the Madagascar specimens are very similar to those of S. maculata De Man [= Geosesamra maculatum ( De Man 1892) ], the meri of which are relatively wide with convex anterior and posterior margins ( De Man 1892 pl. 21, fig. 19c; Ng and Lemaitre 2017, fig. 2A). This statement may be rather exaggerated, as Voeltzkow’s specimen examined by Crosnier (1965, pl. 3, fig. 2, as Sesarma (Sesarma) gracilipes, CW 18.4 mm, also see p. 1) has not-so-wide ambulatory meri with almost parallel and not foliaceous anterior and posterior margins, but it is possible that the ambulatory meri of Voeltzkow’s specimens are slightly wider than those of Sc. finni s.s. The ambulatory meri of Sc. finni are relatively more slender with parallel anterior and posterior margins ( Alcock and McArdle 1903, pl. 66, fig. 1). In light of these differences, we consider the Madagascar specimens are not Sc. finni and describe them as Sc. malagasy sp. nov. Voeltzkow’s Madagascar specimen (MNHN-B11025) is designated as the holotype.

Crosnier (1965, p. 60) listed five diagnostic characters differentiating Sc. malagasy (as Se. gracilipes ) from Sc. finni : (1) more clearly demarcated regions of the dorsal surface of the carapace (vs regions indicated but not emphasised in Sc. finni ), (2) medially inclined frontal margin (vs almost straight in Sc. finni ), (3) relatively shorter and wider ambulatory legs (vs legs relatively longer and more slender in Sc. finni ), (4) foliaceous ambulatory meri (vs not foliaceous in Sc. finni ) and (5) relatively shorter ambulatory dactyli (vs longer in Sc. finni ). Characters (3), (4) and (5) may be partially based on Lenz’s (1910) statement that the ambulatory legs of the Madagascar specimens are similar to those of G. maculatum .

De Man (1887) was the first to record Sesarma gracilipes from Madagascar. However, he merely mentioned the measurements of his Malagasy specimen in the course of redescribing Sesarma schuetteii (as a junior synonym of Se. gracilipes ). De Man (1887) recognised important diagnostic characters of the Sc. gracilipes complex, such as the presence of a large median protuberance around the bases of the fingers of the palm, a longitudinally traversing row of granules on the upper surface of the palm, and the ornamentation on the occlusal margin of the immovable finger of the chela, which are not shared with Sc. malagasy . Further examination is necessary to identify De Man’s (1887) Malagasy specimen.

Scandarma malagasy can be easily distinguished from Sc. gracilipes by its anteriorly aligned four postfrontal lobes of the carapace ( Figure 26 (a); Crosnier 1965, pl. III (2)), proportionately stouter cheliped ( Figure 26 (d); Crosnier 1965, pl. 3(2)), interrupted row of granules on the upper surface of the male palm ( Figure 26 (d); Crosnier 1965, fig. 95); less produced protuberance on the outer surface of the palm near the bases of fingers ( Figure 26 (c); Crosnier 1965, fig. 95); and more concave lateral margins of the male pleon ( Figure 26 (b); Crosnier 1965, fig. 80).

Ecological note

Scandarma malagasy is an arboreal species. Cumberlidge et al. (2005) found Sc. malagasy on phytotelmata of Pandanus leaf axes at heights between 15 and 17 m above the forest floor.

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).

Figure 24. Scandarma papua sp. nov. a, b, RMNH.CRUS.D. 45517, male, 15.4 × 16.7 mm (Hollandia, Papua New Guinea); c, NHM 1922.11.9.2–5, female, 11.3 × 12.8 mm (Huon Gulf, Papua New Guinea). a, pleon; b, right G1, ventral view; c, right vulva. Scale bars: a= 5 mm; b, c= 1 mm.

Figure 25. Scandarma finni (Alcock, 1900). Holotype, ZSI, female, 11.0 × 11.0 mm (Andamans). Photographed by Santanu Mitra, ZSI. a, carapace, dorsal view; b, cephalothorax and chelae, anterior view; c, thoracic sternum and pleon, ventral view.

Figure 26. Scandarma malagasy sp. nov. Holotype, MNHN-B11025, male, 17.0 × 18.4 mm (Madagascar). a, cephalothorax, dorsal view; b, cephalothorax, ventral view; c, left chela, outer view; d, left chela, upper view.