Phyllidiopsis sphingis Brunckhorst, 1993

Yonow, Nathalie, 2012, Opisthobranchs from the western Indian Ocean, with descriptions of two new species and ten new records (Mollusca, Gastropoda), ZooKeys 197, pp. 1-130 : 61

Phyllidiopsis sphingis Brunckhorst, 1993 Fig. 28, Plates 77, 78

Phyllidiopsis sphingis Brunckhorst, 1993: 72, pl. 8H (Hawaii, Guam, Papua New Guinea).

Material.

Maldives: 17 mm (SH-7, "yellow rhinophores"), Fehigili, Lhaviyani Atoll, 30 m depth, 05 March 1991, leg. S Harwood; 19 × 10 mm (MDV/AB/96/18, "pale blue, no tubercles, rhinophores cream/pale yellow"), Yacht Tila, near Medufinolhu, South Malé Atoll, 10 m depth, 09 May 1996, leg. RC Anderson & SG Buttress.

Description.

Both specimens well relaxed, virtually identical to each other with black linear pattern composed of four lines: median pair merges between rhinophores and extends to margin anteriorly, posteriorly they remain separate to anus or meet outer lines at level of anus. Outer lines straight medially but scalloped laterally in extensions to margin; scallops not symmetrical on each side, with five on left and six on right on both specimens. Collectors’ sketches identical to illustration in Brunckhorst, 1993; although only one collector comments on blue colour, both comment on ochre-yellow rhinophores, visible in photographs of both specimens. Anal papilla ochre, very near posterior margin. Photograph of 19 mm specimen (Plate 77) shows central area between black lines to have been blue, outer scalloped areas were granular white with blue spots along margin. Faint orange tinge behind rhinophores (and generally) is a photographic artefact.

The specimens, both preserved in formaldehyde, are very different: one is perfectly marked as if alive, with extended rhinophores and black markings (17 mm, Plate 78). The second appears ‘bleached’ and translucent, to the point where the black spicules aligned in the central region above the yellowish gut are perfectly clear (Fig. 28A). Ventrally, the head is typical of species of Phyllidiopsis , a large fused unit with the grooves of the tentacles just visible in the pigmented specimen; spicules visible along foot margin and on hyponotum (Fig. 28B). The hyponotum, foot sole, and gills are cream coloured.

Internally, the digestive anatomy is typical of the genus: the solid pharyngeal bulb has a flat end anteriorly and tapers posteriorly. The tubular pharynx is narrow and turns on itself to pass through the nerve ring before joining the muscular oesophagus, which is banded and brown-black. There is a long narrow cream oesophagus which enters the digestive gland at approximately the one third mark (fig. 28C). The anal papilla is slightly swollen.

Distribution.

This is the first record of Phyllidiopsis sphingis for the Indian Ocean. Both specimens are small, but within the range reported for West Pacific specimens (4-23 mm). They differ from the Pacific records which have blue pigment only on the mantle skirt. The species in the Maldives is similar to Phyllidia koehleri in its small size, a ridged dorsum rather than a tuberculate one, and with the anus located very far posteriorly.