Visayax osteodictyon, Mendoza & Ng, 2008

Mendoza, Jose Christopher E. & Ng, Peter K. L., 2008, New Genera And Species Of Euxanthine Crabs (Crustacea: Decapoda: Brachyura: Xanthidae) From The Bohol Sea, The Philippines, Raffles Bulletin of Zoology 56 (2), pp. 385-404 : 392-395

Visayax osteodictyon , new species

( Figs. 3 , 4 , 9B )

Material examined. – Holotype: 1 male (6.3 × 4.3 mm) (NMCR- 27508), Station S22, hard ground covered with sand, 15–22 m,

9°29.4'N 123°56.0'E, Pamilacan Island , coll. by Panglao 2004 Marine Biodiversity Project, 21 Jun.2004 .

Paratypes: 2 females (7.4 × 5.3 mm) ( ZRC 2008.0753 ), Station B 14, reef slop with overhangs, 24m, 9°33.2'N 123°48.3'E, BBC Point , Panglao Island , coll. by Panglao 2004 Marine Biodiversity Project, 1 Jun.2004 ; 1 male (6.6 × 5.1 mm) ( ZRC 2008.0754 ), Station B 6, coral patches, 12–14 m, 9°31.1'N 123°41.3'E, Black Forest , Balicasag Island , coll. by Panglao 2004 Marine Biodiversity Project, 4 Jul.2004 ; 1 male (2.3 x 1.7 mm) ( ZRC 2008.0218 ), Station B 17, reef wall with small caves, 3–21 m, 9°37.5'N 123°46.9'E Bingag , Panglao Island , coll. by Panglao 2004 Marine Biodiversity Project, 19 Jun.2004 ; 1 male (3.3 x 2.2 mm) ( ZRC 2008.0219 ), Station B 39, reef wall with small caves, 17–25 m, 9°32.8'N 123°42.1'E, Pontod Lagoon 1, Panglao Island , coll. by Panglao 2004 Marine Biodiversity Project, 2 Jul.2004 .

Description. – Carapace ( Fig. 3A ) broader than long; regions well-defined; 1M, 2M and 2F fused and raised, culminating in a dorsally directed tubercle on 2M; sections of branchial region—3L and 5L—raised into dorsally-projecting tubercles; 3M and 1P distinct, 4M indistinct; entire dorsal surface covered by network of fused granules forming a reticulate pattern, with short setae sparsely distributed at their bases; suborbital region eroded with several small depressions; subhepatic and pterygostomial regions with low, discrete granules. Front deflexed ventrally, appearing truncate, shallowly bilobed from dorsal view; lobes broadly triangular, projecting medially, separated by a wide U-shaped median cleft that continues as a shallow median groove in the frontal region; laterally curving toward inner orbital angle, separated from it by a short groove. Supraorbital region granulose; margin mildly serrated, relatively short, not clearly meeting anterolateral margin, without distinct external orbital tooth. Suborbital margin mildly serrated, outer edge connected to anterolateral margin by a ridge consisting of fused granules. Orbits small, width about 0.1 times carapace width; eyestalks short, distal edge with cornea lined with small, tooth-like granules; corneas well developed. Anterolateral margin strongly arcuate, granulose, appearing irregularly serrated; anteriormost part not meeting supraorbital margin but curving into pterygostomial region where it eventually disappears close to anterolateral corner of buccal cavity; posterior end forming distinct, angular junction with deeply concave posterolateral margin. Anterior portion of posterolateral margin subparallel to frontal margin, and continues as a curve to meet posterior margin. Last ambulatory leg coapted against concavity in posterolateral margin. Junction with posterior carapace margin defined by a granular, upwardly and outwardly projecting tooth; posterior carapace margin straight.

Antennules ( Figs. 3C , 4A ) folding almost transversely. Basal antennal segment large, subrectangular, granulose, almost occupying entire space between antennular fossa and internal orbital angle, orbital hiatus completely filled; long flagellum arising from distal margin, almost reaching outer edge of orbit. Posterior edge of epistome ( Fig. 4D ) slightly undulate, with very shallow, rounded median projection, lateral regions with slight depressions. Endostome without any discernible ridges.

Outer surface of third maxilliped ( Figs. 3B , 4B ) granulose, eroded. Merus subquadrate, median length about half that of ischium, with 2 shallow depressions on either side of a submedian, granular ridge; margins with small granules, anterior and external margins slightly concave, internal margin straight; anteroexternal angle rounded. Ischium subrectangular, inner margin with granules and short, stiff setae; with deep, longitudinal median sulcus, with smaller longitudinal depression anterolateral to it, adjacent to anteroexternal margin; separated from basis by distinct suture. Exopod granulose, tapering toward distal end which almost reaches anterior edge of merus, flagellum long.

Surface of male thoracic sternum ( Fig. 3B ) eroded, with reticulate pattern of ridges and depressions similar to dorsal carapace surface; large distinct depression just anterior to telson of abdomen, no discernible suture within, smaller depressions seen on either side of abdomen; anterior region relatively elongate. Sternites 1 and 2 completely fused into triangular plate, separated from sternite 3 by deep transverse suture. Sternites 3 and 4 partially fused, with partial suture seen near anterior edge of cheliped coxae. Abdominal cavity deep, sternal condyle on sternite 5 slightly nearer to suture with sternite 4, abdomen reaching to imaginary line joining posterior edge of cheliped coxae.

Chelipeds ( Figs. 3A, 3D ) similar, subequal. Fingers shorter than palm, cutting edges with 4 or 5 teeth, tips pointed. Dactylus slightly curved, with three rows of granules, continuing distally as ridges and separated by shallow grooves along its length, base granulose. Fixed finger, slightly deflexed with 2 rows of granules continuing as ridges and broad submarginal groove on outer surface continuing from palm; base granulose and pigmented. Palm outer surface eroded in reticulate pattern similar to dorsal carapace surface, upper margin irregular, wedge-like and granulose, lower margin slightly convex and granulose; inner surface relatively smoother, with fewer and smaller granules; pigmentation on base of fixed finger continues into lower portions of palm outer and inner surfaces forming a dark patch. Carpus short, dorsal and ventral surface eroded, reticulate, inner distal angle with low triangular tooth. Inner surface of fingers, palm and carpus coapted against anterolateral margin of carapace. Merus granulose, slightly longer than carpus, with rectangular, ventro-distal tooth apposed against carpus.

Ambulatory legs ( Figs. 3A , 4C ) relatively short, first leg longest, coxa-to-dactylus length about 0.7 times carapace width, sparsely setose. Merus subrectangular, subtriangular in cross-section; anterior and posterior edges, especially fourth ambulatory leg, lined with large, pointed granules; dorsal surface in fourth ambulatory leg with reticulate pattern of fused granules, others finely granular. Dorsal surface of carpus reticulate, with row of pointed granules on serrated anterior edge. Propodus subrectangular, rugose, anterior and posterior edges serrated in most legs. Dactylus slightly curved inwards, dorsal surface and edges covered with small spines, short setae; terminates distally in curved chitinous claw.

Male abdomen and telson ( Fig. 4E ) with reticulate pattern of fused granules and depressions. Telson rounded; lateral margins convex. Segment 6 subquadrate, about 1.5 times length of telson, lateral margins convex. Segments 3–5 completely fused, without any trace of sutures; lateral margins markedly concave. Segment 2 subtrapezoidal, segment 1 trapezoidal without transverse ridge.

G1 ( Fig. 4F–G ) long and slender, mostly straight, curving outward and tapering distally; terminally located opening bordered by 2 lamellar folds; several long, thick and stiff simple setae located subdistally; basal external region with row of stiff simple setae, surrounded by finer setae.

Live colouration. – The carapace and pereiopods ( Fig. 9B ) are basically white. The fused granules forming the reticulate pattern on the carapace, chelipeds and ambulatory legs are variably tinged light pink. There are also small, discrete spots or smudges of dark orange-brown on carapace, palm of chelae, and anterior edge of merus and carpus of ambulatory legs. The lower part of outer and inner surfaces of palm of the chelae is black while both fingers of the chelae are white.

Etymology. – The specific epithet osteodictyon derives from two Greek words, “osteon” which means bone, and “dictyon” which means net, characterizing the reticulate sculpturing—reminiscent of spongy bone tissue—on the carapace, pereiopods and other surfaces of this species. Used as a noun in apposition.

Remarks. – Visayax osteodictyon , new species, is superficially similar to the various species of Glyptoxanthus A. Milne- Edwards, 1879, particularly in the sculpturing of the carapace and pereiopods (cf. Rathbun, 1930: 263, pls. 107–109). It is easily distinguished from the type species, Glyptoxanthus erosus ( Stimpson, 1859) , by having a networked, anastomosing pattern to the fused granules ( Figs. 3A, D , 4C, E ), whereas in G. erosus , the fused granules tend to take a more vermicular pattern and are more closely spaced. The front of G. erosus has two deep lateral notches, giving it a quadridentate appearance (vs. two simple, broadly triangular lobes in V. osteodictyon , Fig. 3A ); there are no dorsally directed tubercles on the carapace (vs. present, Fig. 3A ); there are oblique ridges in the endostome (vs. absent); there is a visible median longitudinal suture on male thoracic sternite 4, just anterior to the telson (vs. absent, Fig. 3B ); the palm of the chela is stouter and more robust (vs. more slender, Fig. 3A, D ); and while the G1 is similar to those seen in species of Euxanthus : it is much longer, the distal end is blunt, with only one subterminal seta, and the terminus folds over the opening forming a triangular flap (vs. distal end tapering, with several subterminal setae and no triangular flap, Fig. 4F–G ).

Visayax osteodictyon is thus far known only from the type locality, Pamilacan Island, and nearby islands of Panglao and Balicasag, all of which are in the Bohol Sea, central Philippines. It has been collected at depths ranging between 3 to 25 m, in sandy substrate and in coral reef walls. It has been observed to occur together with Rizalthus anconis , new species, and V. estampadori , new species, in reef walls from at least one station (B17).

Figures

Fig. 3. Visayax osteodictyon, new genus, new species, male holotype (NMCR-27508) (6.3 × 4.3 mm): A, dorsal view; B, ventral view; C, frontal view; D, left chela, outer surface.

Fig. 4. Visayax osteodictyon, new genus, new species, male holotype (NMCR-27508) (6.3 × 4.3 mm): A, frontal view, left side, showing antenna, antennule and orbit; B, left third maxilliped, external view; C, left fourth ambulatory leg; D, epistome; E, abdomen and telson; F, left G1, external view; G, left G1, internal view. Scale bars: A–G = 0.5 mm.

Fig. 9. Live or freshly killed colouration of: A, Rizalthus anconis, new genus, new species, female paratype (MNHN- B30700) (11.2 × 7.3 mm); B, Visayax osteodictyon, new genus and new species, paratype male (ZRC 2008.0219) (3.3 × 2.2 mm); C, Visayax estampadori, new genus and new species, male holotype (NMCR-27509) (6.7 × 4.6 mm); and D, Hepatoporus pumex, new species, male holotype (NMCR-27510) (8.0 × 5.7 mm).