This species has been observed on Reunion, Mauritius, Mayotte and Seychelles Islands

Order : Nudibranchia Suborder : Euctenidiacea Superfamily : Doridoidea Family : Chromodorididae Distribution : Indian Ocean. Maximal size : 35 mm Abundance : From time to time on the rocky coast Species characteristics : The background colour is milky lemon yellow. There is a narrow white border to the mantle and inside there is a band of reddish-purple. Diffuse black patches between the purple border and the black lined central region. The gills have a uniform translucent orange coloration
	Showing species characteristics...	Sully Bachel Reunion, La Possession, 4 m, 1 February 2009, size :35 mm

See more about : Hypselodoris nigrolineata variability in Southwest Indian ocean
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Remarks :

Identification confirmed by Bill Rudman
    Our specimens present some variations, the coloration of the gills and the rhinophores is more red than orange, and some of our specimens haven't gills with a uniform coloration. And the background color is more whitish than milky lemon yellow.
    Synonymous : (according Worms)
          - Chromodoris nigrolineata, Eliot, 1904

Bibliographic data :

Hypselodoris nigrolineata is rather similar in colour to the Western Pacific species Hypselodoris maritima.

The central region of the dorsum has a distinctive pattern of black lines, a few running the complete distance from the rhinophores to the gills, but many of them only covering part of the distance. This lines generally run parallel to the body axis. Between the region of the black lines and the purple border there are a number of difffuse greyish patches, about five on each side.     There are 11 gills and they are simple. They form a complete circlet     Running along each side of the foot there is purple line from each side which joins dorsally at the posterior end. The region above and enclosed by the the line is yelow, while the region outside, bordering the foot, is white. The sole of the foot is white     Other species of Hypselodoris with dark blackish lines include Hypselodoris nigrostriata, Hypselodoris maritima, Hypselodoris kanga and Hypselodoris zephyra.

References :

Bill Rudman Seaslug site : Sea Slug Forum : Hypselodoris nigrolineata

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. (1977) Chromodorid opisthobranch Mollusca from East Africa and the tropical West Pacific. Zoological Journal of the Linnean Society 61 : 351-397.
    Rudman, W.B. (1982) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris quadricolor, C. lineolata and Hypselodoris nigrolineata colour groups. Zoological Journal of the Linnean Society 76 : 183-241

Other photos of Hypselodoris nigrolineata :

Sully Bachel Reunion, Cap La Houssaye, 8m, 1 November 2008, size : 30 mm. Three specemens observed during the same dive... In this specimen the gills aren't uniform orange... And the background color is more whitish than milky lemon yellow. Presence of numerous longitudinal black lines.

Sully Bachel Reunion, Cap La Houssaye, 8 m, 22 November 2008, size : 25 mm A specimen with a low number of longitudinals black lines, and a light milky lemon yellow coloration on the dorsum.

Sophie Darnis "Sea Fan Valley" Poste de Flacq, Mauritius, 15-20 m, 8 May 2009, size : 12 mm Like in Reunion specimens, this specimen present some variations, the coloration of the gills and the rhinophores is more red than orange, and some of it hasn't gills with a uniform coloration. Presence of a light milky lemon yellow coloration on the dorsum.

Maurice Jay Reunion, A few years ago at Cap La Houssaye

Christophe Mason-Parker Seychelles, Mahé, Corsaire Reef, 12 m, July 2013, size : 10 mm A mating Behavior

See more about : Hypselodoris nigrolineata variability in Southwest Indian ocean

Mayotte, Hypselodoris nigrolineata, at Longoni, by Norbert Verneau