Scandarma gracilipes (H.Milne Edwards, 1853)

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 : 481-488

Scandarma gracilipes (H. Milne Edwards, 1853), comb. nov.

( Figures 7 (c), 19–21)

Sesarma impressa ? junior: Hombron and Jacquinot 1842 –1854 (1846), pl. 6, fig. 5.

Sesarma gracilipes H. Milne Edwards 1853 , p. 182 [type locality: Tonga]; Jacquinot and Lucas 1854, p. 72; De Man 1887, p. 645, 663.

Sesarma compressa ? junior: H. Milne Edwards 1853, p. 182 [incorrect spelling of Sesarma impressa H. Milne Edwards, 1834 –1840 (1837)]

Sesarma schuetteii Hess, 1865, p. 24 , pl. 6, fig. 11*; Kingsley 1880, p. 217; Haswell 1882, p. 109.

Labuanium gracillipes [sic]: Serène and Soh 1970, p. 402; Ng et al. 2008a, p. 221 (part).

Labuanium schuetteii: Ng et al. 2008a, p. 221 .

Not Scandarma gracilipes : Sesarma jacquinoti ; Ortmann, 1894b, p. 718 = Geosesarma angustifrons (A. Milne-Edwards 1869) (See Remarks on Sc. gracilipes ).

Material examined

Lectotype. MNHN-B3947 , male, 16.6 × 17.3 mm, Vavao (Vava’u, Tonga) (simultaneous neotype of Sesarma schuetteii Hess, 1865 , designated herein).

Others. NHM 1877.24, 1 male, 17.5 × 17.8 mm, Lifu , Loyalty Islands, coll. S.J. Whitmee; NHM 1936.10.2.1–2, 1 male, 17.5 × 18.3 mm, 1 female, 14.7 × 16.2 mm, Lunga , Guadalcanal Island, Solomon Islands; ZRC 2018.0053 , 11 males, 10.8 × 11.3–17.6 × 18.2 mm, 7 females, 10.1 × 11.3–15.7 × 17.7 mm, back mangrove near boatshed of Vanuatu Maritime College , Luganville, Espiritu Santo, Vanuatu, coll. P.K.L. Ng, H.H. Tan, S.H. Tan and J.C.E. Mendoza, 11 September 2006; ZRC 2018.0054 , 7 males, 10.3 × 10.8–13.1 × 14.3 mm, 5 females, 9.6 × 10.8–11.1 × 11.9 mm, 1 ovig. female, 11.3 × 12.7 mm, 1 juvenile, 6.4 × 7.0 mm, Vanuatu, coll. SANTO 2006 expedition; RUMF-ZC-5014, 1 male, 14.8 × 16.1 mm, 6 females, 9.6 × 10.7–14.0 × 15.2 mm, Vanuatu, coll. SANTO 2006 expedition; ZRC 2018.0056 , 1 male, 12.8 × 13.7 mm, Vanuatu,coll. SANTO 2006 expedition; ZRC 2015.0517 ,female,16.6 × 18.5 mm, Espiritu Santo, Vanuatu, 6 November 2006; MNHN, 1 male 12.1 × 13.0 mm, 1 female 12.8 × 13.9 mm, Vanuatu, coll. SANTO 2006 expedition .

Redescription

Carapace ( Figure 19 (a)) subsquarish, 1.02–1.13 times (mean = 1.07, n = 36) as wide as long, lateral margins slightly divergent posteriorly. Dorsal surface slightly convex longitudinally and transversely, glabrous, regions poorly defined; posterolateral regions sloping. Front deflexed at anterior margin of postfrontal lobes, distally recurved, directed anteriorly, frontal margin gently concave medially, overhanging onto antennular septum and fossae. Two pairs of postfrontal lobes present, lateral lobes slightly exceeding mesial lobes anteriorly in large individuals ( Figure 19 (a)); anterior margins of all lobes relatively close to but never reaching frontal margin in dorsal view; 1 pair of short lobes posterior to lateral pair of postfrontal lobes. External orbital angle blunt, directed anteriorly, without longitudinal ridge on verntral surface; lateral margins of carapace weakly undulate, with traces of 2 rudimentary epibranchial teeth. Antennular septum wide, short. Orbit, in dorsal view, tilted J-shaped, median part of supraorbital margins oblique; infraorbital margin cristate, mesial end forming triangular inner orbital tooth, directed dorsoanteriorly. Suborbital crista straight, granulated, setose. Suborbital, pterygostomial, subhepatic regions with reticulate mat of setae.

Epistome long, setose, posterior margin with 3 triangular lobes, lateral lobes sharper, directed anteroventrally, median lobe directed ventrally.

Ocular peduncle ( Figure 19 (a)) cylindrical; cornea moderately large, as broad as peduncle. Antennule with rounded basal article. Antenna with wide, ellipsoidal basal article; antenna entering into orbit through space between inner orbital tooth and front.

Mxp3 ( Figure 20 ) with relatively narrow subtriangular ischium, ovoid merus, leaving long, wide rhomboidal hiatus between them; flagellum of exopod reaching just anterior to mesial margin of merus.

Chelipeds ( Figure 19 ) symmetrical in both male and female; male chelipeds larger. Male cheliped with merus subtriangular in cross section, upper and lower-inner margins keeled; upper margin with shallow concavity subdistally, forming angle behind concavity, lower-inner margin weakly serrate, subdistally with triangular lobe; lower-outer margin serrate, with distal sub-pentagonal lobe near articulation with carpus; outer surface covered with short rows of granules; inner surface with 2 longitudinal rows of soft setae; carpus ( Figure 19 (a,c)) with granulated upper surface,inner angle blunt; palm ( Figure 19 ) swollen; outer surface ( Figure 19 (b)) granulated, granules smaller on lower part; distally sloping smooth area around bases of fingers well delimited, large median protuberance present proximal to sloping surface; upper surface ( Figure 19 (a,c)) with 1 gently sinuous, longitudinally traversing row of small granules, and with few shorter, subparallel rows of granules on inner side; inner surface swollen, with oblique row of granules from upper distal angle to middle, and with large granules medially; thick rim extending along occlusal margin of immovable finger to dactylar articulation on both outer and inner surfaces, thick rims of both outer and inner surfaces not interrupted near dactylar articulation.Immovable finger almost straight,gradually tapering towards tip;occlusal margin lined with elevation over proximal two-fifths (3–5 teeth on elevation), followed distally by 4 or 5 teeth,distal quarter with 2 large teeth; lower margin with irregular row of small teeth. Movable finger with distal part strongly curved downwards; occlusal margin lined with large proximal 3 teeth, followed distally by entire margin or small teeth, and 1 large subdistal tooth; inner side of upper margin regularly lined with flat, rounded granules, these granules becoming smaller proximally and distally. Tips of both fingers corneous, hoof-like. Subdistal tooth of movable finger fitting between 2 subdistal teeth of immovable finger when closed.

Ambulatory legs ( Figure 19 (a)) long, P3 and P4 longest, P4 merus 0.73–0.92 times (mean = 0.81, n = 35) CL. Tufts of soft setae present between P1–5 coxae, of them tufts between P2–4 coxae larger than others. Meri with distal anterior corner toothed, followed by subdistal tooth, and with short setae near anterior and posterior margins. Propodi with longer setae on inner and outer margins, setae black proximally, yellowish distally, distal inner part with small patch of short black setae in P2 and P3. Dactyli gently curved distally, margins with dense row of long setae that are similar to longer setae on propodus.

Male thoracic sternum ( Figure 20 ) transversely wide, sternites 1–4 fused, 2/3 and 3/4 indicated superficially by distally produced row of granules and horizontal groove, respectively. Sternite 2 setose. Male sternopleonal cavity reaching distal third of bases of cheliped coxae; margin of sternopleonal cavity on somite 4 rimmed except for posterior end, posterior end of rim thick, slightly produced posteromesially, produced part of rim adjacent to articulation of pleonal somite 6 and telson when pleon closed; lateral slope of sternopleonal cavity below non-rimmed part on sternite 4 produced mesially, posteriorly accomodating distal end of G 1 in situ. No sternal button for locking mechanism on sternite 5. Penis sternal.

Male pleonal somites 1 and 2 short, wide, somite 3 widest, lateral margins of somites 3–6 forming gradually narrowing curvature; telson rounded distally, slightly longer than somite 6 ( Figure 19 (a), 20).

G1 ( Figure 21 (b)) short, almost straight, stout, narrowed medially, distal end with dorsolaterally directed and wide corneous process. G2 short.

Vulvae ( Figure 21 (c)) located on distal three-fifths of sternite 6, anterior margin adjacent to thoracic sternal suture 5/6, ellipsoidal, margin rimmed except for posteromesial corner, double-rimmed anteromesially, sternal vulval cover developed from anterolateral margin, covering almost entire vulva, except for slit-like gap on posteromesial corner, sternal vulval cover produced ventrally as earlobe-like structure.

Variation

Small individuals with all postfrontal lobes aligned anteriorly; lobes close to but never reaching frontal margin in dorsal view (e.g. CW 12.0 mm) ( Figure 17 (b)).

Colouration

In life, very similar to that of Scandarma lintou (see above). There are, however, minor differences in the posterolateral margins of the carapace (yellow but partially interrupted by black patches) and the outer surface of the chela (dark red) ( Figure 7 (c)).

Distribution

South Pacific: Vavao, Viti Islands (Vava’u?), Tonga [type locality]; Lifu, Loyalty Islands; Vanuatu; Lunga, Guadalcanal Island, Solomon Islands ( Hombron and Jacquinot 1842 – 1854 (1846); H. Milne Edwards 1853; present study). Erroneous records: Sydney ( Hess 1865 as Sesarma schuetteii ); Madagascar (De Man 1887, table on p. 664).

Remarks

Examination of the lectotype ( Figures 19 , 20 ; see below) as well as other specimens ( Figure 21 ) of Sesarma gracilipes H. Milne Edwards 1853 confirms that Se. gracilipes possesses the generic characters of Scandarma as defined here, and the species is now referred to the genus. ‘ Sesarma gracilipes ’ has been widely recorded from the Indo-Pacific regions, but at least two undescribed species have been included under this name (here described as Sc. malagasy and Sc. papua , see below), and Labuanium schuetteii ( Hess, 1865) is synonymised under Sc. gracilipes . To stabilise the taxonomy of Sc. gracilipes and allied species, a male specimen (MNHN-B3947) from Vavao (Vava’u) is here designated as lectotype.

The nomenclature of Sesarma gracilipes H. Milne Edwards 1853,needs explanation. Sesarma gracilipes first appeared as a figure in a plate of ‘Zoologie.Voyage au Pôle Sud et dans l’Océanie sur les corvettes l’Astrolabe et la Zélée pendant les années 1837–1838–1839–1840’ ( Hombron and Jacquinot 1842 –1854 (1846), pl. 6, fig. 5; see Clark and Crosnier 2000 for published year) and captioned in a footnote as ‘S[esarma] IMPRESSA? Junior (Edw.)’.The figured crab,however, clearly differs markedly from Sesarma impressum H. Milne Edwards, 1834 –1840 (1837) (currently the type species of Sesarmops Serène and Soh,1970 ). Henri Milne Edwards (1853, p. 182) realised that the figured crab represented a new species, and formally named it Sesarma gracilipes . Jacquinot and Lucas (1853) [see Clark and Crosnier (2000) and Holthuis (2002) for its publication date] also used the name ‘ Sesarma gracilipes ’ in their work and noted

Les genres et les espèces portant une † sont décrits pour la première fois dans ce travail; ils ont été presque tous créés par M.H. Jacquinot et figurés par lui dans l’Atlas, à l’exception du Sesarma gracilipes , qui appartient à M. Milne Edwards,.. ..(4)

This means that both Jacquinot and Lucas (1853) and Milne Edwards (1853) used the same name in the same year. Clark and Crosnier (2000) noted that Jacquinot and Lucas (1853) might have been published at the end of 1853. The exact publication date of H. Milne Edwards (1853) from Annales des Sciences Naturelles, Zoologie, is also unclear; the paper was published as the second issue of 2 volumes published in 1853, implying that it was published possibly in late 1853. Further study is needed to confirm which authorship has priority. The present study tentatively adopts ‘ Sesarma gracilipes H. Milne Edwards 1853 ’ following Holthuis’s (2002, p. 421) opinion.

Ng et al. (2008a) listed Sesarma compressum Jacquinot, 1853 , as a junior subjective synonym of Labuanium gracilipes . Ng et al.’s (2008a) authorship of ‘ Jacquinot 1853 ’ was copied from the synonymy list of Se. gracilipes by H. Milne Edwards (1853, p. 182), which included the name ‘ Sesarma compressa ? junior ’. There is no publication ‘ Jacquinot 1853 ’, and the authorship of the name must be attributed to the work of Jacquinot and Lucas (1853) (see Holthuis 2002). We have not been able to find any taxon named ‘ Sesarma compressa ? junior ’ and are of the opinion that Milne Edwards (1853, p. 182) had merely misspelled the name ‘S[esarma] IMPRESSA? Junior (Edw.)’ which first appeared in the footnote of Hombron and Jacquinot (1842 –1854 (1846), pl. 6, fig. 5). We therefore treat ‘ Sesarma compressa ? junior ’ as an incorrect spelling of the original name (see ICZN 1999, Article 33.3).

Sesarma jacquinoti Ortmann, 1894 , was described on the basis of one female from ‘Südsee’ and one male and one female from Tahiti. Tesch (1917, p. 155) regarded it as conspecific with Se. gracilipes . Marie Meister from the Musée zoologique de la ville de Strasbourg was kind enough to take photographs of a syntype male (MZS Cru1895) and a syntype female (MZS Cru1896) of Se. jacquinoti from Tahiti. Both major (right) and minor (left) chelae of the male ( Figure 22 ) have a short but strong vertical ridge on the inner surface of the palm, and a relatively slender and gently incurved dactylus. The male also has a wide and rounded median concavity of the front, gently concave anterolateral margins with small epibranchial tooth and relatively narrow pleonal somites 5 and 6. The female specimen agrees well with the male specimens except for sexual characters. These characters confirm that Se. jacquinoti is in fact conspecific with Geosesarma angustifrons (A. Milne-Edwards 1869) (see comparative material of this species examined). Sesarma jacquinoti is here formally synonymised under G. angustifrons . The systematic position of G. angustifrons is also problematic and it is certainly not a species of Geosesarma as currently defined. Paulay and Starmer (2011, p. 11) recommended transferring G. angustifrons to Sesarmops for now, an action we agree with. The male specimen from Tahiti (MZS Cru1895) is here designated as the lectotype of Sesarma jacquinoti .

The taxonomic identity of Sesarma schuetteii Hess, 1865 , is herein reassessed, because the taxon was once synonymised with Scandarma gracilipes by De Man (1887). In spite of the action by De Man (1887), Serène and Soh (1970) resurrected Hess’s taxon as a good species (as Labuanium shuettii ) without comment. Hess (1865) noted that the type locality of Se. schuetteii was Sydney, although he did not specify how many specimens were available to him for study. Sesarma schuetteii has not since been collected from eastern Australia, and McCulloch (1913) and Davie (2002) questioned the existence of the taxon there. Furthermore, Davie (2002, p. 221) noted the type material of Se. schuetteii was likely collected from the islands of the south-west Pacific (see also discussion by Ng 2012, p. 268, for Hess’s species Circulium rotundatum ).

Wilhelm Hess of the Zoologische Museum Göttingen, Germany, studied the collection made by Rudolf Schütte in Australia. A part of Schütte’s collection is known to have been exchanged by De Man in Leiden,and what was left of the remaining collection was transferred to Senckenberg Museum ( Fransen et al. 1997; Davie 2002). We tried to locate the type material of Se. schutteii in the Naturalis, Leiden, and Senckenberg Museum in which collections of the Göttingen Museum are now deposited, but no specimen corresponding to Hess’s material was found. It is known, however, that the Swedish Museum of Natural History (Naturhistoriska Riksmuseet) has the holotype of Pagurus minutus Hess, 1865 ; ( Sandberg and McLaughlin, 1993), although why it is there is not certain. Rasmus Hovmöller and Mattias Forshage of the Swedish Museum of Natural History kindly searched their collections for more material of Hess but found no other specimens. There are several old brachyuran specimens in the museum dating back to Hess’s time, but none of the data corresponds to his type material. The type specimen of Se.schutteii is,therefore,certainly lost. The original descriptions of Se. schuetteii by Hess (1865) and the subsequent redescription by De Man (1887), who examined the type specimen of Se. schuetteii at the Göttingen Museum, clearly showed the presence of a strong protuberance on the outer surface of the palm near the bases of the fingers, a proximal elevation on the occlusal margin of the immovable finger,and two distal teeth on the occlusal margin of the immovable finger ( Hess 1865, pl. 6, fig. 11; Figure 19 (d)), characters which are diagnostic of Sc. gracilipes s.s. ( Figure 19 (b,c)). To stabilise the nomenclature of Sc. gracilipes and Se. schuetteii , we here designate the lectotype of Sc. gracilipes as the neotype of Se. schuetteii , making the latter name an objective junior synonym of the former.

‘ Sesarma gracilipes ’ has been widely recorded, from Vavao (= Vava’u, Tonga) to Madagascar, by many authors, but our study shows that there are at least four species under this name. The distributional range of what we here refer to as the Se. gracilipes complex can be roughly divided into 4 regions: (1) the South Pacific to Solomon Islands, (2) from Louisiade Archipelago to New Guinea Island, (3) eastern Indian Ocean (Atjeh, Nicobaren and Pulau Nias), and (4) western Indian Ocean ( Madagascar). All the specimens we examined from (1) the South Pacific localities represent Sc. gracilipes s.s. The specimens from (2) Louisiade Archipelago to New Guinea Island are markedly different from Sc. gracilipes s.s. and recognised as a new species, Scandarma papua sp. nov. (see below). Specimens recorded from (3) the eastern Indian Ocean (Atjeh, Nicobaren and Pulau Nias) and (4) the western Indian Ocean ( Madagascar) will be discussed in the Remarks on Sc. finni and Sc. malagasy sp. nov., respectively.

De Man (1902, p. 507) identified material from Halmahera (Patani) and Ternate as ‘ Sesarma gracilipes ’. He said that his specimens have cristae of the upper surface of the cheliped palm that are separated into three parts. Tesch (1917, p. 155) examined material from Andai ( Papua New Guinea) and Amboina, identified as ‘ Se. gracilipes ’, and also mentioned this interrupted crista. Those specimens are clearly not Sc. gracilipes or Sc. papua sp. nov., as these two species have a single crista in the cheliped palm. It is necessary to re-examine material studied by De Man (1880, 1902) and Tesch (1917) to fully clarify the specific identity of their material.

Although many references in the literature have used the names ‘ gracilipes ’ and ‘ schuetteii ’, it is difficult to fully clarify the specific identities of material reported in those references ( Table 2 ). They are treated as incertae sedis for the moment, and the material will need to be re-examined to ascertain precise identities.

Ecological note

The recently collected specimens from Vanuatu were all found in low shrubs and small trees near a swampy area several hundred metres from the sea, with thick grass in the undergrowth. All the plants were less than 10 m tall. All the crabs were caught at night, after sundown, foraging on the plants.

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 17. Dorsal view of carapace of small individuals of Scandarma species. a, Sc. lintou, RUMF-ZC -2024, female, 12.9 × 13.6 mm; b, Sc. gracilipes, RUMF-ZC-5014, female,11.2 × 12.0 mm; c, Sc. papua, NHM 1922.11.9.2–5, female, 11.3 × 12.8 mm.

Figure 19. Scandarma gracilipes (H. Milne Edwards, 1853), comb. nov. a–c, lectotype of Se. gracilipes, MNHN-B3947, male, 16.6 × 17.3 mm (Tonga); a, habitus, dorsal view; b, right chela, outer view; c, right cheliped, upper view; d, holotype of Sesarma schuetteii Hess, 1865 (now a junior synonym of Sc. gracilipes), outer surface of right chela (after Hess 1865, pl. 6, fig. 11).

Figure 20. Scandarma gracilipes (H. Milne Edwards, 1853), comb. nov. Lectotype, MNHN-B3947, male, 16.6 × 17.3 mm (Tonga). Cephalothorax, ventral view.

Figure 21. Scandarma gracilipes (H. Milne Edwards, 1853), comb. nov. RUMF-ZC-5014 (Vanuatu). a, b, male, 14.8 × 16.1 mm; c, female, 14.0 × 15.2 mm. a, pleon; b, left G1, ventral view; c, right vulva. Scale bars: a= 5 mm; b= 1 mm.

Figure 22. Lectotype of Sesarma jacquinoti Ortmann, 1894 [now a junior synonym of Geosesarma angustifrons (A. Milne-Edwards, 1869)]. MZS Cru1895, male, 14 × 15 mm (Tahiti). a, habitus, dorsal view; b, habitus, ventral view. Arrow indicates a vertical ridge.