Cyerce bourbonica, Yonow, Nathalie, 2012

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 : 11-14

Cyerce bourbonica sp. n. Fig. 3Plates 14, 15

Cyerce sp. 2. - Gosliner et al. 2008: 70 (Tanzania, Madagascar, La Réunion, and Aldabra + Pacific).

Cyerce sp. 3. - http://seaslugs.free.fr/nudibranche/a_intro.htm (La Réunion).

Cyerce sp. - http://www.nudipixel.net/photo/00024541/ (Similan Islands, Thailand).

Material.

Holotype: 12 mm alive, 6.5 × 2.5 mm pres. in alcohol, Etang Salé, La Réunion, rocky coast, 1 m depth, 14 December 2009, leg. H. Flodrops, SMF 337104.

Paratypes: approx. 12 mm alive, 4 × 3 mm pres. in formalin (dissected), Etang Salé, La Réunion, rocky coast, 1 m depth, 14 December 2009, leg. H. Flodrops, SMF 337103; 10 mm alive, 4.5 × 2 mm pres. in alcohol, Etang Salé, La Réunion, rocky coast, 1 m depth, 14 December 2009, leg. H. Flodrops, SMF 337205.

Diagnosis.

A multi-coloured Cyerce with approximately 30 inflated, pustular, angular cerata whose margins are pale violet-blue with creamy orange patches and black spots. The head has an orange band on either side and black spots on its frontal margin. The body and cerata are marbled light green and white. Ventrally, the propodium and metapodium each bear a row of small black dots, the former anteriorly and the latter marginally and posteriorly. Size up to approximately 15-20 mm.

Description.

The description of the colour and pattern is based on a series of photographs of the type specimens: body covered in fewer than 30 slightly inflated and tubercular cerata, loosely arranged in transverse rows along each side. Each ceras can be flat or swollen, angular with rounded corners (Fig. 3B, C), semi-translucent beige to green, margins pale blue-violet ‘beaded’ with opaque pale orange pigment, and sub-marginal black spots. The profile is in one plane along the sides but strongly convex at the distal end. Tubercles opaque white, concentrations of larger black spots in lateral swellings. Very few black spots scattered on cerata but yellow spots, olive-green patches, and light green to light brown marbling present. In some photographs, paired dark brown globular patches visible in alcohol-preserved specimens can be seen as circular red-brown patches at bases of cerata (Plate 14, right-hand cerata at level of pericardium). Anterior portion of body marbled: head and rhinophores semi-translucent; eyes clearly visible at bases of rhinophores (Plate 15). Oral tentacles short and recurved. Frontal margin of head with black spots, and behind eyes and rhinophores, coalesced to form a network. Broad orange band on each side of head, outside the black spots. Pericardium immediately behind first two or three rows of cerata, swollen, ochre-coloured, bare of cerata.

The specimens preserved in alcohol are in excellent condition; the paratype in formaldehyde shed 23 larger cerata. It is cream in colour, while the holotype and second paratype are semi-translucent. Dark patch of pigment anterior to swollen pericardium behind rhinophores and faint pigmented patch beyond. Pericardium a large swelling but dissection of paratype in formaldehyde did not reveal vessels and disintegrated with further prodding. Large swollen anal papillae behind right rhinophore near eye in all preserved specimens. Conical penis visible below right rhinophore in alcohol paratype only, no spine apparent at tip. Ventral views well presented in alcohol (Fig. 3A); rhinophores visible, as are head and oral tentacles; propodium with row of black spots along anterior margin, rounded metapodium with a row of black spots all around its edge except anteriorly. Cerata angular with three rounded corners near distal margin. At the base, doughnut-shaped attachment point and small flap beyond (Fig. 3B). Minute pointed papillae located in a band following the contours on both surfaces of the cerata, white in certain angles of light (Fig. 3C). Edges of some preserved cerata appear serrated (Fig. 3C). Brown triangular patch present on flap at base of each ceras in alcohol-preserved specimens. Two dark brown to black bodies inside cerata, formed of very small globules (Fig. 3B,C), near base above and beside attachment point.

Dissection of the formaldehyde-preserved paratype proved impossible as only the outer skin was preserved, the internal organs decomposed. However, the muscular pharynx remained solid and was removed to extract the radula. Radular formula 16 × 0.1.0, nine teeth in the ascending limb and seven teeth in the descending one (fig. 3D). The teeth are typical in shape for Cyerce (e.g. Hamatani (1976) for Cyerce kikutarobabai ), and 170 μm in length. The denticles along the cutting edge are paired, with the first denticles at the tip smaller (fig. 3E). Denticles 1-7 increase in size, while denticles 8-10 decrease, and denticle 11 is just a small bump. The teeth are curved along their long axis and fit closely into the next tooth, the denticles leaving indentations in the underlying shaft. In profile, the shaft is shorter and barely narrower than the cusp (fig. 3D, E).

Remarks.

This distinctive species appears to extend throughout the Indo-West Pacific oceans ( Gosliner et al. 2008). Cyerce bourbonica sp. n. has also been discussed on the Sea Slug Forum based on photographs from Japan, La Réunion, and possibly Hawaii (http://www.seaslugforum.net/find/cyersp3). It is recorded frequently from La Réunion but only from two localities. Cyerce bourbonica sp. n. is clearly distinguishable from the named species of Cyerce previously recorded from the western Indian Ocean, all three species of which are recorded from Mayotte and/or La Réunion (http://seaslugs.free.fr/nudibranche/a_intro.htm). Cyerce elegans Bergh, 1870, is translucent cream to beige (sometimes red) with rounded swollen cerata. The edges of the cerata glisten with faint iridescent scalloped markings and there is usually a blue spot at the base of each. Cyerce pavonina Bergh, 1888, has curved swollen cerata covered in pustules on both surfaces and is pale greenish brown in colour, and the outer and inner surfaces of the cerata differ in colour. Cyerce nigricans (Pease, 1866) is black and has golden spots and a red band on the cerata.

Etymology.

The species is named ‘bourbonica’ after the original name of the island of La Réunion, the type locality. The island was renamed La Réunion in 1793 after the fall of the House of Bourbon (Spain and Luxembourg currently have Bourbon monarchs), but the name was changed back and forth several times until the French revolution in 1848.