Elamena samalensis, Husana, Daniel Edison M., Kase, Tomoki & Mendoza, Jose Christopher E., 2013

Husana, Daniel Edison M., Kase, Tomoki & Mendoza, Jose Christopher E., 2013, A new species of false spider crab of the genus Elamena H. Milne Edwards, 1837 (Crustacea: Decapoda: Brachyura: Hymenosomatidae), from Davao Gulf, Philippines, Zootaxa 3616 (5), pp. 495-600 : 496-500

Elamena samalensis sp. nov.

( Figs. 1–3 )

Material examined. Holotype, 3, 4.7 × 4.2 mm (NMCR 39074), Samal Is., Davao Gulf, Mindanao, Philippines, 6º 58.453’ N, 125º 43.470’ E, intertidal zone, coll. T. Haga & Walter, 14 March 2007. Paratype, Ƥ, 5.5 × 4.8 mm (ZRC 2013.0095), same data as holotype.

Comparative material. Elamena simplidenta Ng & Chuang, 1996: paratype, Ƥ, 7.6 × 6.3 mm (ZRC 1994.4231), Ambon, Moluccas, Indonesia, coll. Snellius Expedition, 10–17 Sep. 1930. Elamena cristatipes Gravely, 1927: 2 Ƥ, 4.0 × 4.7 mm, 4.0 × 4.5 mm (ZRC 1969.11.212-3), Batu Ferringhi, Penang, Malaysia, coll. University of Kuala Lumpur, 1966. Elamena truncata (Stimpson, 1858) : 2 3, 7.7 × 6.9 mm, 8.1 × 7.0 mm, 2 ovigerous Ƥ, 9.6 × 8.0 mm, 8.4 × 6.8 mm (ZRC 1999.0048), Sumiyoshi, Tanegashima, Japan, coll. M. Takeda, 13 June 1975. Elamena vesca Ng & Richer de Forges, 1996: paratypes, 1 Ƥ, 4.9 × 4.5 mm, 1 ovigerous Ƥ, 6.9 × 6.2 mm (ZRC 1994.4285), Marèe à Ouémo, Nouméa, New Caledonia, coll. B. Richer de Forges, 1992.

Description. Carapace ( Fig. 1 A) subpentagonal, broader than long; dorsal surface deeply concave, gastrocardiac groove present but faint, with fine granules covering entire surface. Rostrum truncated, continuous with carapace; anterior margin medially convex; ventral keel partially visible from dorsal view, deep, triangular in lateral view, continuous with prominent interantennular septum; lateral margin of rostrum continuous with anterolateral margin of carapace. Anterolateral margin cristate, dorsally projecting, slightly sinuous, slightly concave near base of rostrum; first anterolateral tooth replaced by slight convexity; second anterolateral tooth moderately produced, angular. Posterolateral margin similarly cristate, dorsally projecting, generally convex, not well demarcated from posterior margin. Posterior carapace margin convex, similarly cristate, dorsally projecting. Postocular tooth distinct, triangular; suborbital region slightly swollen. Pterygostomian regions with 3 prominent lobiform crests, one anterior to base of cheliped coxa, one at anterolateral angle of buccal cavity, one in between largest. Subhepatic area swollen.

Epistome length subequal to breadth, posterior margin thinly crested, sinuous, with median notch. Antennule developed, basal antennular segment with short, rounded antero-external protuberance; interantennular septum strong. Antennae directed anteriorly, antennal spines absent. Eyes well developed, eyestalks short, partially visible at anterolateral margin from dorsal view.

Third maxillipeds ( Fig. 1 E) covering entire buccal cavity when closed; exopod narrow, distal end almost reaching the distal external angle of merus, with distinct flagellum; ischium subquadrate, external margin shorter than internal margin, subequal to length of merus, forming continuous ridged external border with merus; merus subtriangular, with longitudinal ridge along submedian surface, inner margin filled by palp in situ.

Male thoracic sternum wide, finely granular; sternites 1–3 fused, hidden by third maxillipeds, sunken toward buccal cavity; strong transverse ridge at junction of sternites 3, 4; border of sternite 4 with Milne Edwards aperture, distinctly convex; succeeding sternites triangular, slightly inflated; sternoabdominal cavity moderately deep, anterior tip reaching anterior border of sternite 4, without sutures, prominent press-button situated at level between sternites 5, 6.

Male chelipeds ( Fig. 1 G) almost symmetrical, robust; merus rounded in cross-section, with small tooth on dorso-distal end and protrusion on inner distal end; carpus rounded, distal inner angle blunt; chela with swollen palm, fingers equal in length, with pointed tips, distally curving inwards, no wide gape when closed, cutting edges lined with small teeth interspersed with much smaller teeth, with larger subproximal tooth on dactylus.

P2-P5 ( Fig. 1 A & B) relatively slender, rounded except flattened dactyli, P3 longest, P5 shortest; meri, carpi of all legs with acute extension on distal end of anterior margins, surfaces lined with short, bristly setae; dactyli shorter than propodi, distal one-third gently curving inward, terminating in pointed claw; dorsal, ventral margins lined with long setae, with subdistal conical tooth on flexor margin.

Male abdomen 5-segmented, including pleotelson ( Fig. 1 C). Third, fourth abdominal somites fused, gradually narrowed over distal half with convex lateral margins; lateral margin of fifth abdominal somite concave; pleotelson triangular, apex acute, distinctly longer than fifth somite, with depressions on either side just above suture with fifth abdominal somite.

G1 ( Fig. 2 ) with long, twisted shaft; proximal half directed medially then turning laterally, outwardly in winding S-shaped manner; with row of 7 stiff, subterminal setae on dorsal surface.

Female paratype. Carapace with swollen gastric region; second anterolateral teeth more distinct than in holotype. Chelae not swollen and more slender, slight gap between finger, pollex present when closed. Thoracic sternum completely covering ventral area; small vulvae on medial fused plate of thoracic sternum, at level of sternite 4. Female abdomen wide, subcircular, covering entire thoracic sternum; abdomen 6-segmented, pleotelson triangular, apex convex, pleopods present.

Coloration. Carapace color of Elamena samalensis sp. nov. is dark brown while ambulatory legs of male are darker brown and yellowish brown in female ( Fig. 3 ). Both sexes have white spots on the surface of legs in fresh material.

Habitat and geographical distribution. Intertidal to shallow subtidal, depth 0–3 m, under rocks in rocky and sandy substrate. Elamena samalensis sp. nov. is currently known only from its type locality, Samal Island, in the Davao Gulf, Mindanao, Philippines.

Etymology. This species is named after the type locality, Samal Island.

Remarks. Elamena samalensis sp. nov. is morphologically similar to members of the Elamena truncata species-group (viz. Ng & Chuang 1996), such as E. mathoei (Desmarest, 1823) , E. truncata (Stimpson, 1858) , E.

abrolhensis Gordon, 1940 , and E. panglao Naruse, Mendoza & Ng, 2008, in the general form of the carapace, where the rostrum is truncated rather than tapering, the carapace is subpentagonal, and the anterolateral margin of the carapace is slightly convex, and the junction of the anterolateral and posterolateral margins of the carapace (“posterior lateral angle” of Lucas 1980) is angular (see Gordon 1940; Lucas 1980; Ng & Chuang 1996; Naruse et al. 2008). It can be easily distinguished from these congeners, however, by the presence of only one subdistal tooth, rather than two, on the ambulatory dactyli.

Elamena samalensis sp. nov. is most similar to E. simplidenta Ng & Chuang, 1996, in the general form of the carapace, by having a small portion of the rostral keel visible in dorsal view, and in having only one subdistal tooth on the ambulatory dactylus. The latter condition is shared by only one other species, E. cristatipes Gravely, 1927 , although this species can easily be separated from the other two by the shape of its carapace and by the cristate anterior border of its ambulatory propodi (see Gravely 1927: pl. 21 fig. 24; Ng & Chuang 1996: fig. 7). The new species can be distinguished from E. simplidenta by the following morphological features: 1) the rostrum is more projecting and more distinctly separated from the carapace anterolateral margin ( Fig. 1 A) (rostrum less projecting in E. simplidenta ; cf. Ng & Chuang 1996: fig. 11A); 2) the anterior margin of the rostrum is slightly convex medially ( Fig. 1 A) (straight in E. simplidenta ; cf. Ng & Chuang 1996: fig. 11B); 3) the anterior region of the epistome is relatively flat and the posterior region is more produced ventrally, i.e., thicker ( Fig. 1 F) (anterior region forms a transverse ridge, posterior region less produced, i.e., thinner, in E. simplidenta ); 4) the finger tips of the chelae are simple, not bifurcate ( Fig. 1 G) (bifurcate in E. simplidenta ; cf. Ng & Chuang 1996: fig. 11I); 5) the ambulatory legs are relatively longer and more slender, with merus length: carapace length ratio = 0.7, merus length: width ratio = 8.1 ( Fig. 1 A) (relatively shorter and less slender in E. simplidenta , with merus length: carapace length ratio = 0.6, merus length: width ratio = 5.0; cf. Ng & Chuang 1996: fig. 11G); and 6) the apex of the female pleotelson is convex (concave in E. simplidenta ; cf. Ng & Chuang 1996: fig. 11J). The male characters for E. simplidenta are not known. The shape of the male abdomen of E. samalensis sp. nov. is perhaps most similar to that of E. abrolhensis Gordon, 1940 , but the apex of the pleotelson of the former is more pointed and has two hollow depressions on either side just above the suture with the fifth abdominal somite, whereas the latter has a more rounded apex. Furthermore, the lateral margins of abdominal somites 3 and 4 are also convex in the new species, and those of the fifth abdominal somite are concave (lateral margins distally concave for abdominal somites 3 and 4 and convex for abdominal somite 5 in E. abrolhensis ) (cf. Gordon 1940: fig. 7c; Lucas 1980: fig. 8g).

The shape of the G1 of Elamena samalensis sp. nov. ( Fig. 2 ) is closest to that of E. abrolhensis . Both of them are twisted forming an S-shape, but the twisting and curvature of the G1 of E. samalensis sp. nov. is tighter and more pronounced than that of E. abrolhensis (cf. Gordon 1940: fig. 7a; Lucas 1980: fig. 10I). In addition, the distal tip of the G1 of the new species has fewer subterminal setae (cf. Gordon 1940: fig. 7a; Lucas 1980: fig. 10I).

Figures

FIGURE 1. Elamena samalensis sp. nov., holotype, ♂, 4.7 x 4.2 mm (NMCR 39074), Samal Is. A, habitus, dorsal view; B, propodus and dactylus of right P 4, dorsal view; C, abdomen (pleotelson and somites 1 – 5); D, anterior region, ventral view; E, left third maxilliped, external view; F, epistome, anterior view; and G, left chela, external view. Scale bars: A – G = 1.0 mm.

FIGURE 2. Elamena samalensis sp. nov., holotype, ♂, 4.7 x 4.2 mm (NMCR 39074), Samal Is. Right G 1, A, external (ventral) view; B, internal (dorsal) view; C, distal end, external view; and D, distal end, internal view. Scale bars: A, B = 1.0 mm; C, D = 0.2 mm.

FIGURE 3. Elamena samalensis sp. nov., paratype, Ƥ, 5.5 × 4.8 mm (ZRC 2013.0095), Samal Is. Freshly-preserved coloration.