Geosesarma demani ( Bürger, 1893 ) 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 : 509-513

Geosesarma demani ( Bürger, 1893) , comb. nov.

( Figures 31 , 32 )

Sesarma demani Bürger, 1893, p. 625 , pl. 21, fig. 7 [type locality: Siargao , Philippines]. Sesarma (Sesarma) demani: De Man 1902, p . 521; Tesch 1917, p. 146.

Labuanium demani: Serène and Soh 1970, p. 402 ; Ng et al. 2008a, p. 221.

Material examined

Lectotype (present designation). SMF ZMG 614 , male, 15.4 × 15.3 mm, Dapa , Siargao, Philippines, coll. C. Semper, 1863–1864.

Paralectotypes. SMF ZMG 614 , 1 male, 15.2 × 15.4 mm, 1 female, 11.5 × 11.5 mm, same data as lectotype .

Redescription

Carapace ( Figure 31 (a)) squarish, as long as wide; dorsal surface with regions distinct, almost glabrous. Front deflexed at anterior margin of postfrontal lobes at more than 90°; frontal margin bilobed with wide median concavity, each lobe recurved, directed anteriorly, slightly overhanging onto antennular fossae, medially attached with antennular septum. Two pairs of postfrontal lobes sharply defined, serrated, mesial lobes wider than lateral lobes, all lobes aligned anteriorly, mesial lobes partially reaching frontal margin in dorsal view; weak rows of tiny granules posterior to each lobe. External orbital angle sharply pointed anteriorly, followed posteriorly by sharp, thin epibranchial tooth and, if present, a small tubercle (vestigial tooth); tip of first epibranchial tooth placed closer to that of external orbital angle than to tip of second epibranchial tooth; lateral margins of carapace almost parallel. Antennular septum narrow, short, dorsally covered by front.

Orbit, in dorsal view, tilted J-shaped, median part of supraorbital margins oblique; infraorbital margin cristate, with triangular inner orbital tooth, directed dorsoanteriorly. External orbital angle with longitudinal ridge on ventral surface.

Epistome relatively long, posterior margin with 3 triangular lobes, lateral lobes distally rounded, recurved, directed anteroventrally, median lobe directed ventrally.

Eye ( Figure 31 (a)) bulb-like, distally swollen. Antennule with rounded basal article. Antenna with wide, ellipsoidal basal article, antenna entering orbit through space between inner orbital tooth and front.

Mxp3 leaving wide gape between mesial margin of ischia and meri; ischium subtriangular, as long as merus; merus ovoid, with oblique depression mesially lined with setae, setose around base of carpus. Exopod reaching proximal half of merus, with long flagellum.

Male chelipeds ( Figure 31 (a)) subequal and similar. Merus short, triangular in cross section, lower-inner margin granulated, expanded into lamellar form on distal half. Carpus granulated, inner surface with 2 teeth. Male palm ( Figure 31 (b,c)) swollen, length about 1.5 times height, entirely granulated; upper surface ( Figure 31 (c)) without conspicuous ridge or distinct protuberance, but with a few short rows of minute granules; 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. Fingers terminating in pointed corneous tip; occlusal margins lined with large and small teeth. Movable finger with 4 ridges on outer, upper and inner surfaces, outer ridge proximally with small granules, second inner ridge with 10–16 granules. Female cheliped weaker than those of male, carpus unarmed on inner surface.

Ambulatory legs ( Figure 31 (a)) relatively long for genus. Meri compressed dorsoventrally, with subparallel anterior and posterior margins, distal corner of anterior margin angled, followed proximally by sharp subequal tooth, margin between distal corner and subdistal tooth convex. P2 and 3 with black, short setae or tufts of soft setae on distal half of propodi and all margins of dactyi; black short setae only on propodi and dactyli of P4 and P5.

Male thoracic sternum transversely narrow; sternopleonal cavity reaching distal half of bases of cheliped coxae.

Male pleon ( Figure 32 (a)) subtrapezoidal, lateral margins of somites 3–6 sinuous, distal margin of somite 6 concave to accommodate proximal part of telson.

G1 ( Figure 32 (b,c)) slender; terminal process long but relatively wide, flattened and drainpipe-like, directed laterally. G2 ( Figure 32 (d)) short.

Colouration

Live colouration not known.

Distribution

Known only from the type locality, Siargao , Philippines ( Bürger 1893).

Remarks

Sesarma demani Bürger, 1893 , was originally described on the basis of the three syntypic specimens (two males and one female) from Siargao, off north-east Mindanao, Philippines. De Man (1902) also examined one of the syntypes deposited in the Museum of Göttingen and provided with additional morphological information available at that time ( De Man 1902, p. 521). When Serène and Soh (1970) transferred the speciesto Labuanium , they included it in ‘group 1’ together with Se. politum (now referred to Labuanium s.s.), Se. cruciatum (now reassigned to Mindanium ) and Se. rotundatum (now transferred to Circulium ), emphasising the elongate shape of the male pleon in those species ( Figure 32 (a)), a similar shape of the G1 ( Figure 32 (b,c)), and the short dactyli of P2–5 ( Figure 31 (a)). Sesarma demani , however, differs from Circulium in the squarish carapace outline with parallel lateral margins ( Figure 31 (a)) (vs laterally inflated in Circulium , Figure 5 (a)), relatively wide and anteriorly serrated mesial postfrontal lobe (about 2 times wider than lateral lobe) ( Figure 31 (a)) (vs mesial postfrontal lobe about 3 times wider than lateral lobes, with only granulated, non-serrated anterior margin in Circulium , Figure 5 (a)), male pleon rectangular, with the lateral margins of somites 3–6 sinuous, subparallel, abruptly narrowed at distal part of somite 6, distal margin of somite 6 deeply concave ( Figure 32 (a)) (vs bell shaped, with lateral margins of somites 3–5 forming concavity in Circulium , Figure 6 (c)); and G1 relatively short and slender, with laterally directed long terminal process ( Figure 32 (b,c)) (vs G1 relatively long and stout, bent distally, and terminal process short in Circulium ). Bürger (1893, p. 625) noted the similarity between Se. demani and L. politum (as Sesarma ). Indeed Se. demani resembles Labuanium politum in the serrated anterior margin of the postfrontal lobes, with mesial lobes being about 2 times wider than lateral lobes, longitudinally elongated carapace, and the presence of a row of granules on the upper margin of the cheliped movable finger. Sesarma demani , however, differs markedly from L. politum at the genus level in their ambulatory propodi and dactyli (relatively slender vs wide), male pleon (relatively wide, with deeply concave distal margin of somite 6 vs relatively narrow, with only slightly concave distal margin) and G1 (distal beak like-process short, directed dorsally vs terminal process long, directed laterally). As outlined above, Se. demani cannot be assigned to either Circulium or Labuanium .

Sesarma demani has a characteristic G1, with a long terminal process that is wide, flattened and drainpipe-like ( Figure 32 (b,c)), and in this regard it is linked to the following species of Geosesarma : G. amphinome ( De Man, 1899) , G. aurantium Ng, 1995 and G. pylaemenes Ng, 2015 ; Consequently, Se. demani is here transferred to Geosesarma . The diagnostic characters of G. demani from the above three species are carapace shape (about as long as wide vs distinctly wider), shape of male pleon (rectangular vs triangular) and position of the postfrontal lobes (mesial lobes reaching frontal margin vs far behind frontal margin) ( De Man 1899, pl. 12 fig. 16, 16b, c for G. amphinome ; Ng 1995, fig. 1A, H for G. aurantium, 2015 , figs 1A, B, 2A, C, G–K, 3A, 4B, D–G for G. pylaemenes ).

Seven Geosesarma species have been reported from the Philippines: G. vicentense ( Rathbun, 1914) (Palaui Island), G. rathbunae ( Serène, 1968a) (Panay Island), G. protos Ng and Takeda, 1992 (Mindanao) , G. hednon Ng, Liu and Schubart, 2003 (western Cebu), G. lawrencei Manuel-Santos and Yeo, 2007 (Palawan) , G. batak Manuel-Santos, Ng and Freitag, 2016 (Palawan) and G. tagbanua Manuel-Santos, Ng and Freitag, 2016 (Palawan) ( Manuel-Santos et al. 2016; Ng and Lemaitre 2017). Geosesarma demani is superficially similar to G. lawrencei , G. batak and G. tagbanua , but the former differs from the latter three species in its stouter ambulatory legs, concave distal margin of male pleonal somite 6, and shape of the G1 ( Figure 31 (a), 32 vs Manuel-Santos and Yeo 2007, figs 1, 2A, B for G. lawrencei ; Manuel-Santos et al. 2016, figs 1A, B, 2A, B, 3A, B, 4 for G. batak and G. tagbanua ).

Figures

Figure 5. Circulium rotundatum (Hess, 1865). Neotype, USNM 1150304, male, 36.3 × 36.3 mm (Tonga). a, habitus, dorsal view; b, anterior part of cephalothorax, anteroventral view.

Figure 6. Circulium rotundatum (Hess, 1865). Neotype, USNM 1150304, male, 36.3 × 36.3 mm (Tonga). a, right chela, outer view; bright chela, upper view; c, cephalothorax, ventral view; d, meri of right P4 and P5.

Figure 31. Geosesarma demani (Bürger, 1893), comb. nov. Lectotype, SMF ZMG 614, male, 15.4 × 15.3 mm (Siargao, Philippines). a, habitus, dorsal view; b, left cheliped, outer-lower view; c, left cheliped, upper view.

Figure 32. Geosesarma demani (Bürger, 1893), comb. nov. Lectotype, SMF ZMG 614, male, 15.4 × 15.3 mm (Siargao, Philippines). a, pleon and telson; b, left G1, ventral view; c, left G1, dorsal view; d, left G2, ventral view. Scale bars: a= 3 mm; b–d = 1 mm.