This species has been observed on Reunion and Madagascar Islands

Order : Nudibranchia Suborder : Euctenidiacea Superfamily : Doridoidea Family : Chromodorididae Distribution : Western Indian Ocean. Maximal size : 40 mm Abundance : From time to time on the fore reef zone and on the rocky coast Species characteristics : All over the mantle are small translucent pits each with a golden-yellow spot giving the mantle an uneven pitted appearance. At the mantle edge of this nudibranch is a band of purple elongate marks and inside this a diffuse submarginal band of milky yellow The rhinophore stalks are translucent white and the clubs are dark brown or black with white edgings The simple gills are translucent with white edging
	Showing species characteristics...	Photo Alain Barrère Reunion, 1 February 2005

See more about : Sightening and mating periods
   See more about : Goniobranchus alius variability in Southwest Indian ocean

Remarks :

Identification confirmed by Bill Rudman
    Synonymous : (according Worms)
          - Chromodoris alius, Rudman, 1987

Bibliographic data :

The mantle of this nudibranch is creamy-white with six irregular grayish translucent patches interconnected with other elongate translucent patches around the inner part of the mantle skirt.
    The underside is all white except for the mantle edge where the purple shows through from the dorsum
    The gills sit in a spherical ball, which also called a goblet-shape
    Very similar in colour to three other nudibranch : C. aureopurpurea, C. albopustulosa and C. rufomaculata but :

C. aureopurpurea : Was found in West Pacific. The gills are translucent purple or red-brown, and each marginal purple spot has a yellow cap around its inside edge, not a diffuse submarginal band of milky yellow.
    C. albopustulosa : Was found only in Hawaii and Marshall Ids
    C. rufomaculata : Was found in Western Pacific. The golden yellow spots are slightly raised and usually on the white background pigmentation.

For some people these four species of nudibranch may be synonymous in a wide Indo pacific species ( no major anatomical differences between these four species)

References :

Bill Rudman Seaslug site : Sea Slug Forum : Chromodoris alius
   Nudipixel Chromodoris alius

Publications :

Johnson R.F. & Gosliner T.M. (2012) Traditional taxonomic groupings mask evolutionary history: A molecular phylogeny and new classification of the chromodorid nudibranchs. PLoS ONE 7(4): e33479
    Rudman, W.B. (1987) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris epicuria, C. aureopurpurea, C. annulata, C. coi and Risbecia tryoni colour groups. Zoological Journal of the Linnean Society, 90 : 305-407.

Other photos of Goniobranchus alius :

Philibert Bidgrain Reunion, Etang salé on the rocky coast, less 1 m, 26 November 2005, size : 10-12 mm.

Philibert Bidgrain Reunion, Etang salé on the rocky coast, less 1 m, 29 October 2005, size : 15 mm. The gills sit in a spherical ball, which also called a goblet-shape in this nudibranch.

Hugues Flodrops Reunion, "Petit tombant" at Etang salé, 7m, 10 October 2007, size : 20 mm.

Alain-Benoît Rassat Madagascar, Nosy bé, 13 m, size : 25 mm

 More photos from Indian Ocean

See more about : Goniobranchus alius variability in Southwest Indian ocean

Reunion, Goniobranchus alius, at Saint Paul, by Monika Bachel

Reunion, a small specimen of Goniobranchus alius, at Etang salé, by Christophe Cadet