Platydoris cinereobranchiata Dorgan, Valdés, & Gosliner, 2002
Platydoris cinerobranchiata Gosliner et al., 2008: 194 (misspelling).
Material.— RMNH.MOL.131655, RBE Stn 23, Kaitetu, Hitu, 8 m depth, “sturdy red nudibranch that loses its border,” 22.xi.1990, leg. A. Fortuin, 60 × 33 mm pres., photos M. Lavaleye 28-33/34.
Fig. 10. Platydoris cinereobranchiata. a, Head and oral tentacles; b, single lateral radular tooth from central region of the radula; c, reduced and worn outermost four teeth of an old row, the last three showing denticles. Scale bars 25 µm.Platydoris cinereobranchiata Dorgan, Valdés, & Gosliner, 2002: 306, figs 2Q, 20G, 40.
Description.— The stiff flat body has a prominent visceral hump running from the rhinophores to the gills. The opaque white ground colour was overlain with brown dots and reticulations covering all the dorsum, except the cream-coloured edges of the mantle and of the branchial and rhinophoral pockets (pl. 5 fig. 4). The translucent rhinophores had brown edges to the 31 lamellae and white tips. The six tripinnate gills were very open and well separated, the lamellae white with brown edging but no dark lines along the rachides (as do those of P. cruenta p. 927 and P. scabra, p. 929). The gill pocket has damage to the anterior side: lack of colour on the midline is possibly also due to damage, and a large portion of the right side is missing; the foot was white, with brown dots and red patches in life (pl. 5 fig. 4, arrowed). The hyponotum had red patches in life (pl. 5 fig. 4, arrowed).
No red remains in the preserved specimen, either ventrally or dorsally: the dorsum is very finely tuberculate, and the areas between these tubercles are brown, creating the brown reticulate pattern in life. Ventrally, the specimen is speckled brown along a central band on the sole and top of the foot, densest in the crevice between the foot and the mantle and decreasing rapidly towards the mantle edge (pl. 5 fig. 5). A band both dorsally and ventrally on the margin of the foot is devoid of brown spots and has no dark line (as that of P. sanguinea, see pl. 6 fig. 1). The anterior margin of the foot is bilaminate, and the upper lamina is notched in the centre. The head is rounded, densely speckled, and the oral tentacles are relatively large and have fewer speckles towards the tips (fig. 10a). The radula was dissected out and has a formula of 44(+4) × 90.0.90. There is no rachidian and only a few innermost laterals are much smaller than the remaining laterals, which have a large pointed cusp approximately the same size as the base (fig. 10b). The last four teeth in each row are very reduced and much smaller than the other laterals. They are flattened plates, curved and semicircular, with an uneven inner edge in most; denticles are just visible in some teeth (fig. 10c).
Remarks.— The only species of Platydoris with similar brown and red markings in this collection is P. cruenta (see below), in which the dorsum and ventral surfaces have short thin wavy brown lines (see pl. 6 fig. 1). Although Dorgan et al. (2002) clearly state “there is no other species of the genus with this colouration” in their discussion of P. cruenta, they continue to describe several red and brown species: Platydoris formosa (Alder & Hancock, 1864) which has striking red patches on the hyponotum and bright red rhinophores. Platydoris sanguinea (p. 928) is dark red with fairly symmetrical ‘patches of coral sand’ arranged dorsally. They describe P. cinereobranchiata as “tan with very small black spots and large orange-red blotches; the gills and rhinophores are dark purple-brown.” The name is said to refer to the ash-grey colour of the gills, which Gosliner et al. (2008) describe as dark bluish grey; i.e., the colour is variable. The two species, P. formosa and P. cinereobranchiata, are very similar indeed and have been confused in the literature: many of the individuals identified as formosa illustrated by Cobb & Willan (2006), Debelius & Kuiter (2007) and Hervé (2010) are in fact cinereobranchiata. Platydoris formosa has very distinctive and striking rhinophoral and branchial pockets which are bright white marked with large black spots around the rims. The rhinophores are uniformly deep red (rarely pale pink) and have 37 lamellae. The gills are cream with a beige or brown line on the rachis, like those of cruenta (see below) and scabra (p. 929). These characters are very different in cinereobranchiata: the rhinophores are variably coloured in shades of grey-brown with white tips, and have 31 lamellae. The pockets are marked by an absence of pigment, which is very noticeable in dark specimens such as that illustrated by Dorgan et al. (2002, fig. 20C). The gills are creamy with brown pigment on the edges of the lamellae without a coloured line on the rachis. Using these criteria, one is then able to identify photographs of the dorsal view of both species. The original description of cinereobranchiata made no mention of the red patches found ventrally, but this is visible in the ventral view illustrated by Cobb & Willan (2006) and in this specimen (pl. 5 fig. 4, arrowed), but is lost in preservative.
Radular teeth are surprisingly consistent amongst species of Platydoris, and external dorsal and ventral colour pattern is important in distinguishing between species. However, in this case, the last few teeth of cinereobranchiata and formosa differ in both form and size: those of cinereobranchiata are much reduced and bear irregular (denticulate) edges on the cusps while those of formosa decrease regularly in size and have smooth cusps. The last teeth of formosa measure 75µm while those of cinereobranchiata are much smaller, 30µm (this specimen and from Dorgan et al., 2002). This is a new record for Indonesia.