Tunebia hatagumoana (Sakai, 1961) Sakai, 1961

Mendoza, Jose Christopher E. & Ng, Peter K. L., 2011, The Polydectinae Dana, 1851, of the Philippines, with description of a new genus for Lybia hatagumoana Sakai, 1961 (Crustacea: Decapoda: Brachyura: Xanthidae), Zootaxa 3052, pp. 51-61 : 56-59

Tunebia hatagumoana (Sakai, 1961) , comb. nov.

Figs. 1 C, D, 2, 3

Lybia hatagumoana Sakai, 1961: 142 , fig. 2a–d; 1965: 162, pl. 80 fig. 1; 1967: 77, 80; 1976: 505, pl. 180 fig. 3. Serène 1968: 88; 1984: 25. — Miyake 1983: 128, pl. 43 fig. 5. — Baba & Noda 1993: 283, fig. 1. — Tan & Ng 1994: 741. —Ng et al. 2008: 201 (list).

Lybia cf. hatgumonana, Ng et al. 2008: 211, fig. 150.

Material examined. 1 male, 2.9 × 2.9 mm ( ZRC 2011.0771), stn T 2, 152 m, coarse sand, Bolod, Panglao Is., PAN- GLAO 2004, 31 May 2004; 1 male, 3.9 × 3.9 mm ( ZRC 2011.0772), stn T 28, 80 m, Biking-Catarman, Panglao Is., PANGLAO 2004, 1 Jul. 2004; 1 male, 3.2 × 3.2 mm ( ZRC 2010.0147), stn T 9, 97–120 m, fine sand with seagrass, off San Isidro, Panglao Is., PANGLAO 2004, 14 Jun. 2004; 1 male, 3.2 × 3.1 mm ( ZRC 2011.0773), stn CP2408, 121– 137 m, Maribojoc Bay, Panglao Is., PANGLAO 2005, 1 Jun. 2005.

Remarks. The specimens from Panglao ( Figs. 1 C, 2, 3) agree well with the description and illustrations of Sakai (1961: 142, fig. 2a–d) and Guinot (1976: 76, figs. 20K, 22G, pl. 19 fig. 7). The specimen figured in Ng et al. (2008: 211, fig. 150), and included in the material examined here, is from PANGLAO 2004 station T28. A fifth specimen was collected during the LUMIWAN 2008 expedition by dredge from a depth of 105 m (stn DW2861), from off the western coast of Batangas province, Luzon. Although this specimen has not been examined, the livecolour photograph ( Fig. 1 D) is enough to make a definite identification. It is noteworthy that the photo shows a small nudibranch clutched by the left cheliped of the specimen.

The live colouration of this species is distinctive ( Fig. 1 C, D). It consists of assorted polygonal patches of white on the carapace: 1 on each of the protogastric regions, 1 on the metagastric region, 5–6 clustered on the lateral margins of each of the branchial regions, and 2 on the cardiac region. These white patches (smaller in young specimens) are bordered by thin brownish-maroon lines, and the patch on the metagastric region has its apex prominently tipped with a triangle of the same brownish-maroon. The rest of the carapace is yellowish-orange. The pereiopods are indistinctly banded with white and brownish-maroon (except the dactyli); the palm of the chela is bright purple; the distal tip of the ambulatory propodi has a prominent white patch. The corneas are reddish-orange and the eyestalks have one or two maroon lines visible dorsally.

There appears to be some variation in the morphology of the G1 between the Philippine material ( Fig. 3 I, J) and the Japanese type material. Sakai’s (1961: fig. 2c, d) illustration of the G1 shows the distal aperture with an encircling flange (absent in the Philippine material), and does not clearly show the lateral crest on the proximal half (prominent in the Philippine material). This may be due to variation or just how the types were drawn. Also, while Sakai (1961: 144) describes the male abdomen as consisting of 7 free segments, segments 3–5 are immovably fused though traces of the sutures are visible in the Philippine material ( Fig. 3 E). No other obvious variations in morphology and live colouration have been observed. The type material, probably in the Emperor’s Collection of the National Museum of Nature and Science at Tsukuba, Japan, was not examined. For the moment, we regard the Philippine and Japanese material as conspecific.

This deep-water species was previously known only from Japan (type locality: Sagami Bay). Unlike species of Lybia , which have been observed to carry only sea anemones, this species also carries small nudibranchs in its chelae (Sakai 1961; Baba & Noda 1993), which has also been observed in the Philippine specimens as well.

Figures

FIGURE 1. Live colouration of Philippine Polydectinae species. A, Lybia leptochelis (Zehntner, 1894), male, 6.2 × 5.8 mm (ZRC 2011.0762), Pamilacan; B, Polydectus cupulifer (Latreille in Milbert, 1812), female, 16.1 × 13.3 mm (ZRC 2011.0768), Balicasag; C, D, Tunebia hatagumoana (Sakai, 1961), C, male, 3.9 × 3.9 mm (ZRC 2011.0772), Panglao; D, specimen not examined (coll. off western coast of Batangas; stn DW 2861, LUMIWAN 2008).

FIGURE 3. Tunebia hatagumoana (Sakai, 1961); A – H, male, 3.2 × 3.1 mm (ZRC 2011.0773); I – K, male, 3.9 × 3.9 mm (ZRC 2011.0772). A, carapace, dorsal view; B, anterior and buccal area, ventral view; C, right mxp 3, external view; D, anterior thoracic sternum, ventral view; E, abdomen, external view; F, right chela, external view; G, left P 2, dorsal view; H, left P 4, dorsal view; I, J, left G 1, external view (I), internal view (J); K, right G 2, external view. Scale bars: A, B, G, H = 1.0 mm; C – F, I – K = 0.5 mm.