Pilumnus armatus, Komai, Tomoyuki & Motoh, Hiroshi, 2012

Komai, Tomoyuki & Motoh, Hiroshi, 2012, The identity of Pilumnus dofleini Balss, 1933 (Crustacea: Decapoda: Brachyura Pilumnidae), with descriptions of three new species from the Western Pacific, Zootaxa 3305, pp. 1-27 : 12-17

Pilumnus armatus n. sp.

( Figs 8–11 )

Pilumnus dofleini . — Takeda & Manuel 2000: 157 (part), figs 3F, 5.

Material examined. Holotype: male (15.4 x 18.4 mm), NMCR 39035, Visayas, off Panglao, Bohol Sea, Philippines, steep slope of outer reef edge, depth unknown, 2004, tangle net, coll. local fisherman.

Description. Carapace ( Fig. 8 A, B, 10A–D) fairly vaulted, subovoid in general, surface covered with numerous short, stiff setae; greatest width across fourth anterolateral spines, 1.2 times of length; dorsal surface somewhat convex longitudinally, slightly convex transversely, regions weakly defined, surface of regions with several conical spines or spinulose tubercles; cardiac region not particularly elevated, only with few, low tubercles partially obscured by setae; grooves between regions also with short setae. Frontal margin slightly produced, separated medially by wide, V-shaped notch; each frontal lobe divided in two parts by broad hiatus, mesial lobe with 7 subequal minute tubercles, lateral lobes each consisting of small conical spine slightly larger than spines on mesial lobe; inner supraorbital angle with minute tubercle; supraorbital margin with row of small spines, with 2 narrow cleft (one at middle, one near external orbital angle). Anterolateral margin with 4 principal spines (including spinose external orbital angle), these anterolateral spines subequal in size, obliquely erect, each bearing some accessory spines or spinules. Posterolateral margin almost straight, converging towards posterior margin. Posterior part with submarginal row of small but conspicuous tubercles, posterior margin nearly straight. Suborbital margin sinuous with mesial angle weakly produced, with row of small spines. Suborbital region with covering of numerous spinules or spinulose granules; pterygostomial groove lined with distinct granular row along dorsal side. Dorsolateral portion of buccal frame with cluster of spinules.

Orbits ( Fig. 10 A, D) moderately large, slightly obliquely transversal in dorsal view, transverse in anterior view; eyes filling entire orbits. Basal segment of antennular peduncle with 1 obliquely transversal ridge on outer surface, bordering fossa. Antennal peduncle just entering orbital hiatus; second segment with minute tubercle distally on outer surface.

Epistome divided into 4 crested lobes. Endostomal ridges indistinct.

Third maxilliped ( Fig. 10 E) similar to that of P. dofleini . Ischium with mesial margin bearing row of tiny rounded teeth; outer surface finely granular in most part, but mesial part coarsely granular. Merus coarsely granular on outer surface. Carpus with few coarse granules on outer surface. Propodus, dactylus surfaces smooth. Exopod with inner subdistal tooth prominent.

Chelipeds ( Figs 8 A, 9A, 11A–E) slightly unequal, slightly dissimilar with right stouter than left. Anterodorsal margin of basis-ischium fused segment with row of small tubercles. Merus nearly as long as high; upper surface concave to fit lateral surface of carapace; posterodorsal margins crested, each with 2 prominent spines distally and row of much smaller spines; outer (posterior) distal margins each with few minute spinules, ventrolateral outer angle with minute spine; outer (posterior) surfaces with covering of short setae, with spinules along ventral margin; anterior (inner) surface slightly convex, with minute granules along distal margin; ventral margin bluntly carinate, with rows of spinules or minute spiniform tubercles. Carpus with scattered, numerous, conical spines on dorsal surface, inner distal angle with prominent spine. Palm with numerous scattered spines, short setae covering outer surface, inner dorsal margin bluntly carinate with row of spines; ventral surface bluntly carinate, spinulose; inner surface nearly smooth. Fingers crossing at tips. Fixed finger of major cheliped slightly deflexed, curved inward, with row of low, rounded teeth on cutting edge; outer surface shallowly concave medially. Fixed finger of minor cheliped more strongly deflexed than that of major cheliped, with sharply edged, faintly dentate cutting edge. Dactylus weakly curved, with numerous small tubercles or granules proximally; outer surface with blunt median carina flanked by deep longitudinal sulci.

Ambulatory legs ( Figs 8 A, 9A, 11F, G) moderately long, relatively slender for genus (merus of fourth leg about 3.0 times longer than wide); surfaces with covering of minute setae; dorsal (extensor), ventral (flexor) surfaces with sparse, moderately long to long, stiff setae, first leg (second pereopod) longest, about 1.6 times of carapace width. Coxa with low granules on ventral surface. Basis-ischium fused segment with minute tubercles on ventral surface in first to third legs, that of fourth leg (fifth pereopod) with small spinulose tubercles on outer (posterior) surface. Merus with single row of spines increasing in size distally on dorsal (extensor) margin; ventral (flexor) surface flanked by clearly delimited margin each bearing row of small spines or tubercles; outer (posterior) surface unarmed (first to third legs) or armed with many spines or spiniform tubercles arranged in 2 irregular rows (fourth leg). Carpus with single row of spines on extensor surface; outer (posterior) surface with median row of spines. Propodus with 2 or 3 rows of spines or spiniform tubercles on extensor surface; flexor margin unarmed. Dactylus moderately slender, slightly curved distally, terminating in small corneous claws, longer than respective propodus; dorsal margin with 3–6 small spiniform tubercles.

Thoracic sternum ( Fig. 9 B) covered with coarse granules (granules becoming more conspicuous in posterior sternites).

Male abdomen ( Fig. 10 F) moderately narrow, somites 1 and 3 widest. Somite 1 transversely trapezoidal, lateral margins tuberculate, outer surface with numerous small but conspicuous tubercles. Somite 2 subtrapezoidal, narrower than flanking somites, with paired minute tubercles laterally. Somites 3–6 unarmed, smooth; somite 3 broadly trapezoidal, narrowed distally, lateral margin gently convex, unarmed; somite 4 trapezoidal, lateral margins slightly concave; somites 5 and 6 subrectangular, with straight lateral margins. Telson ( Fig. 10 F) triangular with rounded tip, approximately as long as wide, lateral margins slightly convex.

First gonopod ( Fig. 10 G–J) sinuous; distal 0.2 strongly arcuate, hooked in lateral or mesial view, slightly directed laterally in ventral view, gradually tapering, bearing 2 rows of minute stiff setae not extending to apex. Second gonopod similar to that of P. dofleini .

Coloration in life. Not known.

Distribution. Known only from the Bohol Sea, the Philippines; bathymetric range unknown.

Remarks. Pilumnus armatus n. sp. is most similar to P. dofleini , particularly in the general armature of the carapace and abdomen, the shape of the ambulatory legs, armed extensor margin of the ambulatory dactyli, and noticeably arcuate distal part of the first gonopod. Pilumnus armatus n. sp. can be differentiated from P. dofleini , however, in the following characters: the cardiac region of the carapace is not elevated and bears only a few, very low tubercles in P. a r m a t u s n. sp., whereas there are about 10 conspicuous spines or tubercles on the slightly elevated cardiac region in P. d o f l e i n i ( Fig. 8 B versus Fig. 1 B); the outer surface of the palm of major cheliped bears spines or tubercles scattered in P. a r m a t u s n. sp., rather than arranged in irregular rows in P. dofleini ( Fig. 11 A versus Fig. 4 A); the outer (posterior) surface of the merus of the fourth ambulatory leg has several scattered spines in P. a r m a t u s n. sp., but is unarmed in P. dofleini ( Fig. 11 G versus Fig. 4 G); and the distal part of the first gonopod is more strongly arcuate in P. a r m a t u s n. sp. than in P. d o f l e i n i ( Fig. 3 H versus Fig. 10 H).

As mentioned above, the record P. dofleini from Balicasag Island made by Takeda & Manuel (2000) is here referred to P. a r m a t u s n. sp.

Etymology. From the Latin, armatus (= armed), alluding to the armature on the body and thoracic appendages.

Figures

FIGURE 1. Pilumnus dofleini Balss, 1933, male (12.5 x 15.3 mm), CBM-ZC 10621. A, entire animal, dorsal view; B, carapace, dorsal view.

FIGURE 3. Pilumnus dofleini Balss, 1933, male (12.5 x 15.3 mm), CBM-ZC 10621. A, left upper orbital and anterolateral margins, dorsal view (setae omitted); B, frontal margin, anterodorsal view (setae omitted); C, posterior margin of carapace and first abdominal somite, posterodorsal view (setae omitted); D, left anterior part of carapace and cephalic appendages, anterior view (setae omitted); E, left third maxilliped, ventral (outer view; setae partially omitted); F, abdomen and telson, ventral view (setae omitted); G, left first gonopod, ventral view; H, same, mesial view; I, same, distal part, ventral view; J, same, mesial view; K, same, lateral view; L. left second gonopod. Scale bars: 2 mm for A, B, D, F; 1 mm for C, E, G, H; 0.5 mm for I – L.

FIGURE 4. Pilumnus dofleini Balss, 1933, male (12.5 x 15.3 mm), CBM-ZC 10621. A, right major chela, outer view; B, carpus of right major cheliped, dorsal view; C, merus of right major cheliped, outer view; D, left minor chela, outer view; E, merus of left minor cheliped, outer view; F, left third ambulatory leg (fourth pereopod), posterior view; G, left fourth ambulatory leg (fifth pereopod), posterior view). Setae omitted. Scale bars: 2 mm.

FIGURE 8. Pilumnus armatus n. sp., holotype, male (15.4 x 18.4 mm), NMRC 39035. A, entire animal, dorsal view; B, carapace, dorsal view.

FIGURE 9. Pilumnus armatus n. sp., holotype, male (15.4 x 18.4 mm), NMRC 39035. A, entire animal, ventral view; B, thoracic sternum and abdomen, ventral view.

FIGURE 10. Pilumnus armatus n. sp., holotype, male (15.4 x 18.4 mm), NMRC 39035. A, left upper orbital and anterolateral margins, dorsal view (setae omitted); B, frontal margin, anterodorsal view (setae omitted); C, posterior margin of carapace and first abdominal somite, posterodorsal view (setae omitted); D, left anterior part of carapace and cephalic appendages, anterior view (setae omitted); E, left third maxilliped, ventral (outer) view (setae partially omitted); F, abdomen and telson, ventral view (setae omitted); G, left first gonopod, ventral view; H, same, mesial view; I, same, distal part, mesial view; J, same, lateral view. Scale bars: 2 mm for A – F; 1 mm for G, H; 0.5 mm for I, J.

FIGURE 11. Pilumnus armatus n. sp., holotype, male (15.4 x 18.4 mm), NMRC 39035. A, right major chela, outer view; B, carpus of right major cheliped, dorsal view; C, merus of right major cheliped, outer view; D, left minor chela, outer view; E, merus of left minor cheliped, outer view; F, right third ambulatory leg (fourth pereopod), posterior view; G, left fourth ambulatory leg (fifth pereopod), posterior view (broken at articulation between carpus and propodus). Setae omitted. Scale bars: 5 mm for A – E; 2 mm for F, G.