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This species has been observed on Reunion (?), Mayotte and Madagascar

Order : Nudibranchia Suborder : Euctenidiacea Superfamily : Doridoidea Family : Chromodorididae Distribution : Tropical Indo-West Pacific Maximal size : 35 mm Abundance : Species characteristics : The mantle is pale brown, grayish to purplish with a network of black lines surrounded groups of low white pustules    The rhinophores have a stalk speckled with opaque white and the clavus is vivid green (most often), greenish yellow, brown orange or watery orange     The gills are speckled with opaque white basally and apically with the same color of the rhinophore    The undersurface of the mantle is flushed with purple anteriorly and the foot has a dark violet line along each side where it joins the mantle
	Showing species characteristics...	Photo Rozenn Gildas Mayotte, Passe en S, 30 m, 13 March 2010

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

Remarks :

Identification confirmed by Bill Rudman and Nathalie Yonow
   Goniobranchus conchyliatus from the Indian Ocean, has been considered a sibling species of Goniobranchus geometricus from the Western Pacific. But Valda Fraser (June 2000) clearly shows that both species co-exist in the western Indian Ocean (south coast of Kwazulu-Natal). Colin Ogden maked also the same observation in South Africa (Sodwana Bay, 2005). And also in Mayotte and Reunion (?) Islands ( see G.conchyliatus)
    On the posterior end of the foot of Goniobranchus geometricus we often observed two black lateral lines that join in the midline, which is not the case on our specimens of Goniobranchus conchyliatus. Observation to confirm
    Synonymous : (according Worms)
          - Chromodoris geometrica, Risbec, 1928

Bibliographic data :

The animal vibrates its gill and the front of the head is alternately raised and lowered when the animal is actively crawling
    Black lines on the dorsum were marked with white dots in variable density
    The five to eight, small, simple gills form a complete circle around the anus
    Like Goniobranchus conchyliatus, Chelonaplysilla violacea appears to be the favoured food of this species.
    This species lays a peach to orange loosely coiled spawn mass. The white ova (90-105 µm diameter) occur individually within capsules (105-120 µm)
    Goniobranchus geometricus is similar to Goniobranchus hintuanensis and G. conchyliatus but :

	G. geometricus	G. conchyliatus	G. hintuanensis
Localisation	Tropical Indo-West Pacific	Indian Ocean	Western Pacific
Behavior	They have the distinctive habit of waving the anterior portion of the mantle skirt up and down as they crawl
Gills	The gills are speckled with opaque white basally and apically vivid green (most often), greenish yellow, brown orange or watery orange	The gills are lined with red or reddish-orange.	The gills are a translucent reddish purple colour edged with a dark line of the same colour.
Rhinophores	The rhinophores have a stalk speckled with opaque white and the clavus is vivid green (most often), greenish yellow or watery orange	The rhinophore are uniformly red or reddish-orange with white stalk.	The rhinophores are a translucent reddish purple colour edged with a dark line of the same colour.
Mantle	The mantle is pale brown, grayish to purplish with a network of black lines surrounded groups of low white pustules	The body is pale violet with rounded areas of creamy yellow pustules, and deeper violet and red markings.	The body has a network of pale plum area    Small circles of deep magenta outline 5-8 of the small opaque white rounded nodules on the medium area of the dorsal surface of the animal.
Undersurface of the mantle	The undersurface of the mantle is flushed with purple anteriorly	The undersurface of the mantle is flushed with orange and purple anteriorly	The undersurface of the mantle is flushed with deep purple anteriorly

References :

Site de Bill Rudman : Sea Slug Forum : Chromodoris geometrica
   Nudipixel Chromodoris geometrica

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
    Gosliner, T. and D. Behrens. 1998. Five new species of Chromodoris (Mollusca: Nudibranchia: Chromodorididae) from the tropical Indo-Pacific Ocean. Proceedings of the California Academy of Sciences 50(5): 139-165, 15 figs
    Rudman, W.B. (1977) Chromodorid opisthobranch Mollusca from East Africa and the tropical West Pacific. Zoological Journal of the Linnean Society, 61 : 351-397.
    Yonow, N. (1993) Opisthobranchs from the Maldive Islands, including the descriptions of seven new species (Mollusca: Gastropoda). Revue francaise d'Aquariologie, 20(4) : 97-130

Other photos of Goniobranchus geometricus :

Norbert Verneau Mayotte, Dzaoudzi (le banc de sable), 6m, 14 September 2012, size : 25 mm   The undersurface of the mantle is flushed with purple anteriorly (a) and the foot has a dark violet line (b) along each side where it joins the mantle

Emmanuel Eby Mayotte, Longoni harbourg, 7 July 2007 The gills are speckled with opaque white basally (a) and apically (b) vivid green

Emmanuel Eby Mayotte, Longoni harbourg, 26 May 2007, A very small specimen, about 10 mm

Olivier Le Bris Mayotte, 5 December 2008 A small specimen with : The rhinophores have a stalk opaque white and the clavus greenish yellow (a). The gills are opaque white basally and greenish yellow apically (b). The mantle is pale brown, grayish to purplish with a network of black lines (c) surrounded groups of low white pustules (d)

Alain Diringer Réunion, Pierre au préfet, Saint Gilles, 5 October 2008 This specimen is probably a juvenile of G. geometricus because : The gills and rhinophores are opaque white basally and apically watery orange (a) The mantle is pale brown, grayish to purplish with a network of black lines (c) surrounded groups of low white pustules (d)

Philibert Bidgrain Mayotte, Dzaoudzi, Le Rocher, less 1 m, February 2014, size : 10 mm

See more about : Goniobranchus geometricus variability in Southwest Indian ocean

Mayotte, mating in Goniobranchus geometricus, at Longoni, by Emmanuel Eby

Mayotte, G. geometricus with pale brown orange gills and rhinophores, at Sakouli, by Fabrice Schubert  

Madagascar, Goniobranchus geometricus at Nosy Tanikely, by Hugues Flodrops