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

Order : Nudibranchia Suborder : Euctenidiacea Superfamily : Doridoidea Family : Chromodorididae Distribution : Tropical Indian Ocean Maximal size : 50 mm Abundance : Frequently on the fore reef zone and the rocky coast Species characteristics : They have large purple or purple-brown spots or marks, usually ringed with white to blue white, on a gold brown or durty yellow color mantle It has four colour bands around the mantle edge, an outermost, thinner than the rest, is white, then translucent greyish purple, then another white band and finaly a band of bright golden yellow. The rhinophore stalk is translucent white as are the pointed tips, and the club is a translucent gold with a brownish tinge to the lamellae.
	Showing species characteristics...	Photo Florence Trentin "Cap la Reunion, Houssaye" at Saint paul, 12 m, 17 January 2005, 40 mm.

See more about : Sightening and mating periods
   See more about : Goniobranchus geminus variability in Southwest Indian ocean
   See more about : Pattern modification over time in Goniobranchus geminus

Remarks :

Identification confirmed by Bill Rudman and Nathalie Yonow
    Synonymes : (d'après Worms)
          - Chromodoris geminus, Rudman, 1987

Bibliographic data :

The outside face of the gills is white and the gill lamellae are translucent brown. The inside face is brown on the upper half and white basally with the edge lined with brown. The gill are subquadrangular in section with the gill lamellae on the two edges
    On the underside of the mantle the narrow white band at the extreme edge is visible in our specimen (usually not visible) then the greyish purple band. The inner white and yellow bands (not the yellow band in our specimen) are also present. Inside the yellow band the underside of the mantle and the side of the body are white with purple spots.
    The foot extends nearly one quarter of the body length beyong the posterior portion of the mantle and is a little paler in color, but also covered by large and small spots. It is edged only with a white line.
      When the animal is crawling, it exhibits the very characteristic behavior of raising and lowering the mantle edge rhythmically with the entire edge either being raised or lowered at the same time
    This is one of a group of similarly coloured species which Bill Rudman called the " Risbecia tryoni colour group" which includes Risbecia tryoni , Goniobranchus kuniei, Goniobranchus tritos, Goniobranchus leopardus, Chromodoris cf.geminus and Goniobranchus geminus.
    These other three species are present in the Tropical Western Pacific, and have not yet been observed in Reunion Island.

Goniobranchus geminus	Goniobranchus tritos	Goniobranchus kuniei	Chromodoris cf. geminus	Risbecia tryoni	Goniobranchus leopardus
Tropical Indian Ocean.	Maldives Islands	Tropical West Pacific.	Tropical South West Indian Ocean	Tropical Western Pacific	Tropical West Pacific
They all have large purple-brown spots or marks ringed with white or bluish and often reticulated brownish background
The round spots are uniforme brown-purple					Multiple spots or marks, forming hollow squares, like the leopard fur.
Flat body shape with a wide mantle overlap.				High shape of the body, with a reduced mantle overlap.	Flat body shape with a wide mantle overlap.
Four colour bands around the mantle edge : white (outer), greyish purple, white, then yellow	Two colour bands around the mantle edge : pale cream (outer) then brownish red	A broad purple border, consisting of three slightly different coloured bands	A narrow purple border but absent from some specimens	A narrow purple border with brownish patches around the edge	A narrow purple border
The rhinophore clubs are yellowish	The rhinophores club are ochre	The rhinophore clubs are yellowish	The rhinophore clubs are purple	The rhinophore clubs are brown and bluish	The rhinophore clubs are partially bluish

Material examined by Nathalie Yonow ( see reference/publications).

Two specimens collected from Grand Baie (Mauritius), 5 March 1990, size : 20 and 26 mm.

Material examined by Bill Rudman ( see reference/publications).

Saint Gilles Reef, August 1973, photo only, Paris Museum, (Jay collection, Lot 15)

References :

Bill Rudman Sea slug site : Sea Slug Forum : Chromodoris geminus
   Nudipixel Chromodoris geminus

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. (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.
    Yonow, N., 1989, Red Sea Opisthobranchia 2. The family Chromodorididae (Mollusca, Nudibranchia), Fauna of Saudi Arabia, 10, 290- 309.
    Yonow, N. and Hayward , P. J. (1991). Opistobranches de l'île Maurice, avec la description de deux espèces nouvelles (Mollusca : Opistobranchia) Revue française d'aquariologie herpétologie, 18 (1), 1-30

Other photos of Goniobranchus geminus :

Emmanuel Eby Reunion, Maison verte, Saint Leu, 9 August 2006 Rhinophores details : The rhinophore stalk (a) is translucent white as are the pointed tips (b), and the club is a translucent gold (c) with a brownish tinge to the lamellae.

Philibert Bidgrain Reunion, Etang salé on the rocky coast, less 1 m, 26 November 2005, size : 45 mm Gills detail : The outside face of the gills is white (a) and the gill lamellae (b) are translucent brown. The inside face (c) is brown on the upper half and white basally with the edge lined with brown. The gill are subquadrangular in section with the gill lamellae on the two edges

Philibert Bidgrain Reunion, Etang salé on the rocky coast, less 1 m	Pattern evolution over time 1 to 13 corresponded to some "old purple-brown spots "

Philibert Bidgrain Reunion, Etang salé on the rocky coast, less 1 m, 15 October 2005. When the animal is crawling, it exhibits the very characteristic behavior of raising and lowering the mantle edge rhythmically with the entire edge either being raised or lowered at the same time On the underside of the mantle the narrow white band at the extreme edge is visible in our specimen (usually not visible) then the greyish purple band. The inner white and yellow bands (not the yellow band in our specimen) are also present. Inside the yellow band the underside of the mantle and the side of the body are white with purple spots.

Philippe Cao Van Reunion, Saint Leu, 19 March 2006 A specimen with an abnormal branched gill.

David Caron Reunion, Cap la Houssaye, Saint Paul, 27 April 2006 The foot extends nearly one quarter of the body length beyong the posterior portion of the mantle and is a little paler in color, but also covered by large and small spots. It is edged only with a white line.

See more about : Goniobranchus geminus variability in Southwest Indian ocean

See more about : Pattern modification over time in Goniobranchus geminus

Mauritius Island, Chromodoris Goniobranchus, at Recif Water Lily, by Mathieu Bayon

Reunion, Goniobranchus geminus, at Sainte Rose, by Nicolas Noël

Reunion, Goniobranchus geminus, at Saint Gilles, by Sophie Darnis 

Réunion, Goniobranchus geminus like an ostrich, at Saint Gilles, by Eva Fontaine  

Réunion, spotted foot of Goniobranchus geminus, at Saint Leu, by Emmanuel Eby 

Reunion, Goniobranchus geminus, at Etang salé, by Christophe Cadet  

Reunion, Goniobranchus geminus, at Le Port, by Thierry Gomilla  

Mayotte, Goniobranchus geminus, at Sakouli, by Fabrice Schubert  

Madagascar, three Goniobranchus geminus, at Sainte Marie, by Sully Bachel  

Seychelles, Goniobranchus geminus, at Mahé, by Christophe Mason-Parker