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This species has been observed on Reunion, Mauritius and Madagascar Islands

Order : Nudibranchia Suborder : Euctenidiacea Superfamily : Polyceroidea Family : Aegiridae Distribution : Tropical indo-West Pacific. Maximal size : 60 mm Abundance : Seldom on the fore reef zone Species characteristics : Adult animals are uniformly yellow Small irregular pustules cover the upper surface of the body. The rhinophores of this Notodoris are smooth, simple and relatively small The gills are about one-third of the way down the body from the anterior end, partially hidden by three large lobes.
	Showing species characteristics...	Photo Emmanuel Eby Reunion, Saint Leu, 26 September 2004

See more about : Sightening and mating periods

Remarks :

Identification confirmed by Nathalie Yonow
    Synonymous : (according Worms)
               - Aegires citrinus (Bergh, 1875)

Bibliographic data :

Adult animals are uniformly yellow and can be distinguished from other species of the genus Notodoris by their lack of black pigmentation, although, juveniles ( < 25 mm ) appear to have black rhinophores (see Bill Rudman sea slugs site).
    It can also be distinguished by the position of its gills, which are about one-third of the way down the body from the anterior end. In other species of Notodoris, the gills are approximately midway down the body.
    It is generally found on coral reefs from the low intertidal to about 40m in depth
    It is commonly reported to feed on yellow calcareous sponges of the genus Leucetta, its remarkable skin texture is almost identical to the structure of the sponge on which it feeds.
    According to Bill Rudman, one behavioural difference between Notodoris citrina and the other well-known yellow species (Notodoris gardineri and Notodoris minor) is that whereas those latter two are almost always nestled on their food sponge ( Pericharax ), Notodoris citrina is often found on the substrate, crawling between the smaller colonies of its food sponge .

References :

Bill Rudman Seaslug site : Sea Slug Forum : Notodoris citrina

Publications :

Bergh, L.S.R. (1875). Neue Nacktschnecken der Südsee. 3. Journal de Museum Godeffroy, 3(8) : 53-100 (185-232).
    Marshall, J.G. & Willan, R.C. (1999). Nudibranchs of Heron Island, Great Barrier Reef. A survey of the Opisthobranchia (Sea Slugs) of Heron and Wistari Reefs . Backhuys Publishers, Leiden, The Netherlands, 257 pp.
    Wells, F.E. & Bryce, C.W. (1993). Sea slugs and their relatives of Western Australia . Western Australian Musum, Perth. 184 pp.

Other photos of Notodoris minor :

Alexandre Laporte Madagascar, Sainte Marie, Ile aux Nattes, 3 m, 31 August 2017, size : 5 mm   juveniles ( < 25 mm ) appear to have black rhinophores (a) (see Bill Rudman sea slugs site).

Emmanuel Eby The same that the upper photo In this photo, you can see the three large lobes which partially hide the gills A specimen with small irregular pustules and with little dark pigmentation ! Reunion, Saint Leu, 26 September 2004

Delphine Dupin Reunion, Saint Leu, 04 December 2004   The gills are about one-third of the way down the body from the anterior end, partially hidden by three large lobes. A specimen without small irregular pustules and without any dark pigmentation

Christophe Cadet Reunion, Saint Pierre, 13 m, May 2009 Small irregular pustules cover the upper surface of the body but without any dark pigmentation

Mauritius Island, Notodoris citrina, at Recif corsaire, by Mathieu Bayon

Mauritius, gill detail of Notodoris citrina, at Poste de Flacq, by Sophie Darnis 

Mauritius, retracted rhinophore detail of Notodoris citrina, at Poste de Flacq, by Sophie Darnis  

Reunion, Notodoris citrina without any dark pigmentation, at Trois Bassins, by Cédric Péneau