Plakobranchus ocellatus van Hasselt, 1924 Plate 17

Plakobranchus ocellatus . - Yonow 1990: 288, pl. 2 (Red Sea); Apte 2009: 169, fig. 2a (Laccadive Islands); Richmond 2011: 276 (East Africa).

Placobranchus ocellatus . - Rao 1962: 1, figs. 1, 2e, f (India); Jensen 1992: 283, figs. 23, 24d, e (Red Sea and SW Thailand + Guam, Hawaii).

Material.

Kenya: 25 × 11 mm preserved, Vipingo, 25 miles N of Mombasa, rock pool ELW, 23 September 1984, leg. J Hognerud. - Maldives: 9 mm in length (MDV/AB/96/7, specimen disintegrated, no radula located), Fulidhoo Lagoon, Felidhoo Atoll, 10 m depth on sand, 04 May 1996, leg. RC Anderson & SG Buttress. - Zanzibar: 14 × 8 mm preserved, Matemwe Lagoon, in Xenia sp. and sand near encrusted, partly submerged rock with Didemnum molle and Halimeda sp., 01 March 1995, leg. MD Richmond. - Seychelles: 30 × 10 mm alive (PK-A, one of four individuals preserved), Source d’Argent, La Digue, 1 m depth on broken Acropora sp. behind reef in algal growth, 26 January 1992, leg. P Kemp. - La Réunion and Mayotte: photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Description/Distribution.

Plakobranchus ocellatus has been recorded in excess of 35 mm in the Indian Ocean (Rao 1962). The western Indian Ocean specimens e xamined here conform to the description of Red Sea specimens (Yonow 1990, 2008). Jensen (1992) listed numerous synonyms from the Pacific Ocean, stating that colour pattern and distribution of ocelli are variable in just a single species; however, in 2006 she suggested, "It is possible that a complex of sibling species is involved."

Remarks.

In the Marshall Islands, an interesting commensal association was observed between Plakobranchus ocellatus and the sea cucumber Holothuria atra (Mercier and Hamel 2005); this is the first report of an opisthobranch occurring on an echinoderm species. The authors provide evidence of a real association between the two animals through a set of well-designed experiments and natural observations. In the Indian Ocean Holothuria atra is also a common species, with a similar habitat to Plakobranchus ocellatus, but there are no observations of a similar association.