Gymnodoris subflava Baba, 1949
Gymnodoris subflava Baba, 1949: 135, pl. 12 fig. 44, text fig. 38; Rudman & Darvell, 1990: 50.
Trevelyana ? Bergh, 1905: pl. 5 fig. 15 (no accompanying text) syn. nov.
Material.— RMNH.MOL.131662, RBE Stn 34, Ruhmatiga, Hitu, 3 m depth, 3.xii.1990, leg. K. van Egmond, two very contracted specimens 6 mm and 7 mm and two more extended specimens 10 × 6 mm and 10 × 5 mm, photos M. Lavaleye 39-20/24.
Fig. 7. Gymnodoris subflava. a, Left rhinophore of 10 mm specimen; b, radular teeth near old end, left half of radula, showing one rotated 1st lateral (left of photo), 7 mm specimen; scale bar 50 µm.
Description.— When alive, the body colour was uniformly deep yellow with small slightly darker yellow pustules (pl. 3 fig. 5). The >20 gills are located in the last third of the dorsum and are the same colour as the body. They are arranged in a horseshoe-shape in both the preserved specimens and the photographs, as simple upstanding lamellae. The rhinophores were a darker yellow-orange, and the genital papilla is located just behind and below the right rhinophore. The rhinophores are very bulbous in the preserved material, with eight thick diagonal widely-spaced lamellae and a rounded terminal knob (fig. 7a). The foot appears to have a darker yellow-orange margin in the photographs.
The larger specimen was dissected to extract the radula; the visceral casement is black. The radula is small and compact with the formula 14 (+2-3) × 18.104.22.168.12, and the teeth are minute in comparison to those of G. aurita and G. impudica. The first lateral is not so different from the marginals, with a weaker base and shorter cusp; however, in all rows on both sides, the base of the first tooth is rotated 180o from the outside to the centre of the radula. The cusp still points anteriorly, but is connected to the base along the central line of the radula. The remaining teeth have a strong oval to angular base with a long curved cusp set at almost right angles (fig. 7b).
Remarks.— The gymnodorids are notoriously difficult to identify, and there is no recent taxonomic work reviewing this group. Gymnodoris subflava was described from Japan, and recorded from Hong Kong; this appears to be the second record since the original description, apart from few photographs posted on various internet sites. The black visceral casement, visible through the skin in the living specimens, is diagnostic, as is the open horse-shoe shape of the gill insertions. Bergh’s illustration (1905, pl. 5, fig. 15) of “Trevelyana?” is probably this species, and shows the black visceral casement clearly; the gills in the tiny painting are arranged in an elongated oval. Baba’s (1940) original description is not very detailed, and the radula is different in both formula (27 × 13-22.214.171.124.13-16) and in the shape of the first lateral, which he states is much larger and has a short acutely pointed cusp. His illustration of the rhinophores is like those of this specimen, but that of the gills is not. These specimens are best placed in G. subflava despite radular differences, until further collections with radular diagnoses from other localities provide more information. Currently G. subflava is recorded from Japan, Hong Kong, and now Indonesia.