Ilyoplax pacifica, Wada, 2006

Wada, Jun Kitaura Keiji, 2006, New Species Of Ilyoplax (Brachyura: Ocypodidae: Dotillinae) From The Philippines And Indonesia: Behavioral, Molecular, And Morphological Evidence, Raffles Bulletin of Zoology 54 (2), pp. 373-379 : 374-377

Ilyoplax pacifica , new species

( Figs. 1-5 )

Material examined. – Holotype (one pleopod originally missing): male (5.4 mm) ( ZRC 2006.99 ), the Philippines, Luzon Is., Lucap, coll. K. Wada, 14 Dec.2000 . Paratypes: 5 males (4.4, 4.8, 5.3, 5.5, 6.0 mm) (OMNH-Ar 7099-7103), data as for holotype ; 2 males (4.0, 5.9 mm) (OMNH-Ar 7104, 7105), 2 females (5.1, 5.6 mm) ( ZRC 2006.102 - 103 ), one ovig. female (5.6 mm) (OMNH-Ar 7106), The Philippines, Luzon Is., Lucap, coll. J. Kitaura, 14 Dec.2000 ; 2 males (4.8 mm) ( ZRC 2006.101 ), (6.1 mm) ( ZRC 2006.100 ), The Philippines, Luzon Is., Tanoborg, coll. K. Wada, 12 Dec.2000 ; 2 males (4.8, 6.0 mm) (OMNH-Ar 7107, 7108), Indonesia Celebes, Manado , Munthea, coll. K. Wada, 2 Sep. 2001 .

Description. – Carapace sub-rectangular, regions poorly defined, dorsal surface smooth, or microscopically granular, with sparsely scattered very short setae on postero-lateral regions. Gastro-cardiac groove well defined, cardiac region with a low swelling on either side of mid-line; branchial regions with two short, small transverse ridges close to base of fourth ambulatory leg, each with a row of short setae. Posterior border slightly concave, with a very broad rim.

Front approximately 0.26 × distance between external orbital angles. Frontal margin slightly concave from dorsal view, upper surface with median furrow. Dorsal orbital margin slightly arched, sloping backwards. External orbital angle subacutely pointed, shallow notch present just behind external orbital angle. Lateral margins behind notch sinuate, slightly divergent posteriorly. Lateral margins behind notch in females regularly convex, not sinuous. Lower orbital margin with a large projecting lobe near outer end.

Third maxilliped: merus longer than ischium; lateral and mesial margins arcuate, convergent anteriorly; anterior margin slightly concave, with plumose setae near lateral angle; outer surface smooth, with longitudinal depression adjacent to external margin. Ischium quadrangular; antero-mesial angle produced; outer surface generally smooth, but with a row of plumose setae slanting down from anterior half of ischium towards middle of external margin.

Abdomen: male telson semi-circular, with rounded tip. Sixth segment a little longer and broader than fifth, almost quadrate. Fifth segment constricted near base. Fourth and third segment divergent, third segment broadest, fourth segment slightly longer than third segment. Second segment very short, longer medially than laterally. First segment as long as second, but slightly broader. Lateral margins of abdomen fringed with short setae. Female abdomen typical for congeners.

Chelipeds: merus trihedral in cross-section, inner surface with sparse, short setae, ventral surface smooth, outer surface with a few scattered granules. Male carpus elongated (about 2 × as long as wide), widest proximally, tapering distally; in females carpus short, quadrate. Internal proximal angle of carpus with obtuse tooth, with a small tuft of short setae immediately behind tooth. Chelae elongated (length about 2.5 × height). Palm broadened distally, sharply carinate on upper margin. Outer surface of palm smooth, with granulated ridge adjacent to lower margin extending to about two-thirds of pollex. An accessory ridge of granules arises from tip of finger, extending over whole length of lower outer surface of pollex. Lower surface of pollex between these two lines finely granulated. A granulate line present near tip on inner surface of fingers, extending about mid-length of palm. Dactylus with a broad denticulated tooth on basal half of cutting margin, distal half with fine denticles. Pollex with an even row of teeth on cutting margin that range from large and rounded proximally to denticle-like distally; tips of fingers acute, slightly curved.

Walking legs: third pair longest, fifth pair shortest. Carpus and propodus of first and second pairs very thickly covered with soft simple setae. In last pair, all segments glabrous. Faintly demarcated oval tympana on each merus.

First male pleopod: Pleopod long, slightly curved, apex divided into two short lobes.

Etymology. – The species name, pacifica , is derived from their distribution area, the Pacific Ocean.

Remarks. – In overall appearance I. pacifica , new species, is most similar to I. orientalis and I. tansuiensis . However, the structure of their first male pleopods, shape of their male carapaces, and the shapes of the lobe near the outer end of the lower orbital margins of these three taxa are sufficiently different. The apex of the first male pleopod is distally divided into two short lobes in I. pacifica , but trilobed in the other two species, with the apex being simple in I. tansuiensis , but not in I. pacifica and I. orientalis . The shorter lobe of the pleopod apex is also relatively more expanded in I. pacifica and I. tansuiensis than I. orientalis ( Fig. 3-A ). The lateral margins of the carapace behind the notch are markedly sinuous in I. pacifica and I. orientalis , but is distinctively convex in I. tansuiensis ( Fig. 3-B ). The characteristic lobe near the outer end of the lower orbital margin is acute in I. pacifica and I. tansuiensis but is obtuse in I. orientalis ( Fig. 3-C ).

Habitat. – Obtained from soft mud flats in mid to high tide level at small inlets.

Geographic distribution. – Distributed from the Philippine Islands to Sulawesi ( Indonesia), not overlapping with the two allied species, I. orientalis and I. tansuiensis . Ilyoplax orientalis is currently known from the Malay Peninsula, Malaysia ( Tweedie, 1935, 1950; Tan & Ng, 1994) while I. tansuiensis has been reported from Taiwan, southern China and Vietnam ( Sakai, 1939; Gao & Li, 1985; Dai & Yang, 1991; Fukui et al., 1989; second author, unpublished data).

Color while alive. — Dark brown on dorsal surface ( Fig. 4 ).

Figures

Fig.1 Ilyoplax pacifica, new species,male holotype (ZRC 2006.99).

Fig. 2 Ilyoplax pacifica, new species: A, suborbital margin; B, male abdomen; C, male first pleopod; D, E, magnifications of apex of first pleopod; F, left chela; G, female abdomen. A, C-F, holotype male; B, paratype male (OMNH-Ar 7105); G, paratype ovig. female (OMNHAr 7106).

Fig. 3 Comparison of the form of the first male pleopod, shape of carapace and shape of the lobe near outer side of the infraorbital border among I. orientalis, I. tansuiensis, and Ilyoplax pacifica, new species. A, magnification of apex of first pleopod:Ilyoplax pacifica, new species, paratype male (OMNH-Ar 7105); I. tansuiensis, male (5.2 mm c.b.) (OMNH-Ar 7111), Tanshui, Taiwan, coll. K. Wada, (27 Mar.1996); I. orientalis, male (5.2 mm c.b.) (OMNH-Ar 7109), Ranong, Thailand, coll. K. Wada, (6 Dec.1982). B, side margin of male carapace: Ilyoplax pacifica, new species, paratype male (OMNH-Ar 7105); I. orientalis, male (OMNH-Ar 7109); I. tansuiensis, male (OMNH-Ar 7111). C, dorsal view of characteristic lobe of the infraorbital border: Ilyoplax pacifica, new species, paratype male (OMNH-Ar 7105); I. orientalis, male (OMNH- Ar 7109); I. tansuiensis, male (OMNH- Ar 7111).

Fig. 4 Dorsal view of living Ilyoplax pacifica at Lucap, Luzon Is., the Philippines, 14 Dec.2000.

Fig. 5. A, successive postures of waving display by Ilyoplax tansuiensis. Values above crabs indicate time in second from the initial position (the mean value of 59 wavings, 7 males). Drawings are traced from videotapes; B, successive postures of waving display by Ilyoplax pacifica, new species. Values above crabs indicate time in second from the initial position (the mean value of 100 wavings, 10 males). Drawings are traced from videotapes.