Dolabella auricularia (Lightfoot, 1786)

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 : 8-9

Dolabella auricularia (Lightfoot, 1786) Fig. 2Plate 12

Aplysia rumphii Cuvier. - Rang 1828: 46, pl. 1 (La Réunion).

Aplysia ecaudata Rang 1828: 47, pl. 2 (Papua New Guinea).

Aplysia truncata Rang 1828: 47 (Papua New Guinea).

Aplysia teremidi Rang 1928: 48, pl. 3 figs 1 - 3 (Society Islands).

Aplysia gigas Rang 1828: 48, pl. 3 Fig. 4 (shell only) ("Mer des Indes"; "... this shell differs from the previous species..." transl.) (syn. n.).

Dolabella auricularia . - Bebbington 1974: 73, figs. 7D, E, 8 (Tanzania, Seychelles (Aldabra), Kenya, Zanzibar, Grande Comoro); Gosliner 1987: 48, fig. 28 (South Africa); Yonow and Hayward 1991: 6, figs. 5E, F, 7D, 12A, B (Mauritius); Yonow 1994a: 104, figs. 2B, C, 4H (Maldives); Apte 2009:167: fig. 1j (Laccadive Islands); Richmond 2011: 278 (East Africa).

Dolabella gigas . - Engel 1942: 197, figs. 1-5 ("Indian Ocean" and Mauritius + West Pacific); Eales 1946: 149, figs. 1-8 (Bombay, India) (syn. n.).

Dolabella scapula (Martyn). - Engel 1942: 207, figs. 6-16 ("Indian Ocean," Mauritius, Mozambique + West Pacific).

Material.

Zanzibar: 46 × 28 mm pres., Kizimkazi Dimbani reefs, intertidal, June 1994, leg. Suki/MD Richmond. - La Réunion, Mauritius, and Mayotte: photographs of numerous individuals and two shells http://seaslugs.free.fr/nudibranche/a_intro.htm. - Oman: Muscat, 1-12 April 2009, photo S Kahlbrock. - Seychelles: one individual photographed, Lilôt, NW Mahé, 1988-1989, P Kemp.

Description/Remarks.

Examination of the shell (Fig. 2) identifies the Zanzibar specimen as the tropical Indo-Pacific Dolabella auricularia ; the specimen had rounded tubercles in life, and these remain on the preserved animal. There are only two species of Dolabella , but to date no recent specimens of Dolabella gigas (Rang) have been recorded. The two species are said to differ in shell morphology and internal characters ( Engel 1942, Eales 1946): Bebbington (1974) gave a history of Dolabella gigas and Dolabella auricularia . Engel (1942) listed both species, with slightly different shell morphologies, long and armed or short and unarmed penises, based on one specimen and 13 shells of gigas and many more of auricularia (as scapula). Eales (1946) examined two specimens of Dolabella gigas from India and confirmed the differences in shell morphology but was unable to confirm the presence of spines on the penis.

The radular formulae appear smaller in gigas but it is difficult to make size-for-size comparisons from the literature. This study demonstrates that the shells of three specimens from La Réunion and Zanzibar with rounded tubercles, the external morphology of Dolabella gigas , prove to be identical to Dolabella auricularia (P Bidgrain and M Jay, pers. comm., see http://seaslugs.free.fr/nudibranche/a_intro.htm for shell photos). Looking at the many shells illustrated by Engel (op. cit.) and Eales (op. cit.), there appears to be a clinal variation from one extreme to the other. Smooth and hirsute specimens were recorded together from Mauritius ( Yonow and Hayward 1991) and both spiky and warty specimens were recorded from the Maldives ( Yonow 1994a); all shells examined were similar, which eliminates the previously divisive external morphologies. It is probable that some of the shells of Dolabella gigas illustrated in the literature are extremes or aberrant; there appears to be only one record of penis spines, which remains unconfirmed. If this is considered an error, any differences between the two species are eliminated: it seems extremely unlikely that there would be two very large species of Dolabella distributed together in the same regions, and both are here considered the same species.

Note.

The Maldives specimen and shell listed in Yonow (1994) are deposited in The Natural History Museum, London (NHMUK 20110444), and not in the Australian Museum, Sydney, as stated in that paper due to subsequent postal security regulations.