Version française...

This species has been observed on Reunion and Madagascar Islands

Order : Nudibranchia Suborder : Euctenidiacea Superfamily : Doridoidea Family : Chromodorididae Distribution : Known from : Tanzania and north-eastern of South Africa. Maximal size : 15 mm Abundance : Seldom if ever ... Species characteristics : This white species is characterised by a red outer line and a yellow-orange inner line at the mantle edge.     An additional purple/bluish margin line is present around the edge of the foot     The rhinophore are white with a red mark along the upper half of the anterior and posterior midlines     The gills are white with a red line along the inner and outer edges    About midway down the mantle on each side there is a thicker reddish purple patch which gives the body a "waist".
	Showing species characteristics...	Photo Sully Bachel Reunion, La Possession, 6m, 3 January 2009, size : 15 mm

See more about : Sightening and mating periods

Remarks :

Identification confirmed by Bill Rudman
    Looks like Thorunna cf. horologia but T. horologia is white with orange then red marginal band and the rhinophore are white with only a red mark along the upper half of the anterior and posterior midlines
    Synonymous : (according Worms)
          - No other name

Bibliographic data :

The "hour-glass" appearance of the mantle gave the idea of horologia (= clock) for its species name.
    The whole of the body is white with a deep red band right at the edge of the mantle with a second band of orange on the inside. Halfway back along each side the red and orange border is replaced by a rounded purple mark which give the body the illusion of being narrower or having a waist
    The gills are simple and arranged in a circle around the anus. They wriggle rhythmically.
    The oral tentacle are tipped with a washy purple and the edge of the anterior foot has a broad band of the same color. There is a pale purple/bluish submarginale band on the posterior part of the foot.
    These species have similarity with Goniobranchus albonares and Goniobranchus verrieri but :
               - In Goniobranchus verrieri, the marginal line doesn't thickens midway down the body. And an additional purple/bluish margin line is present around the edge of the foot only in Thorunna horologia
               - In Goniobranchus albonares the rhinophores and gills are white. And an additional purple/bluish margin line is present around the edge of the foot only in Thorunna horologia

References :

Bill Rudman Seaslug site : Sea Slug Forum : Thorunna horologia
   Nudipixel Thorunna horologia

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. (1984) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: a review of the genera. Zoological Journal of the Linnean Society 81 : 115-273.
    Rudman, W.B. (1985) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris aureomarginata, C. verrieri and C. fidelis colour groups. Zoological Journal of the Linnean Society, 83 : 241-299.
    Gosliner, T. (1987) Nudibranchs of Southern Africa. A guide to opisthobranch molluscs of Southern Africa . California: Sea Challengers & Jeff Hamann.

Other photos of Thorunna horologia :

Sully Bachel Reunion, La Possession, 6m, 3 January 2009, size : 15 mm (a) The rhinophore are white with a red mark along the upper half of the anterior and posterior midlines (b) About midway down the mantle on each side there is a thicker reddish purple patch which gives the body a "waist". (c) There is a pale purple/bluish submarginale band on the posterior part of the foot. (d) The gills are white with a red line along the inner and outer edges

Maurice Jay Reunion, Saint Paul

Sully Bachel Réunion, Saint Benoît, 10 m, 15 May 2010, size : 18-20 mm

Alain-Benoît Rassat Madagascar, Nosy bé, Pain de sucre, 8 m, 9 April 2015, size : 30 mm

Sully Bachel Reunion, Le Barachois, 6-7 m, 30 November 2014   In this atypic specimen the rhinophore became enterely orange. Variation of Thorunna horologia with strange rhinophore coloration or variation of Thorunna cf. horologia without purple coloration on the mantle or the proof that these two species are in fact only one species.... so Thorunna horologia

Alain-Benoît Rassat Madagascar, Nosy Bé Variation of Thorunna horologia with strange rhinophore coloration or variation of Thorunna cf. horologia without purple coloration on the mantle or the proof that these two species are in fact only one species.... so Thorunna horologia

If you have taken a photo of this species in South West Indian Ocean, please Contact us...