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

Order : Pleurobranchomorpha Superfamily : Pleurobranchoidea Family : Pleurobranchidae Distribution : Indo-West Pacific Maximal size : 230 mm Abundance : Seldom on the reef flat zone Species characteristics : This species is quite variable in colour, ranging form almost completely dark brown (like this specimen) to white with pale brown spots. The thick mantle of this very large pleurobranch bears numerous, low pustules that are group in a characteristic way; one large pustule is surrounded with a ring of six to eight smaller pustules. Posteriorly, when it is crawling actively, the mantle was raised and folded to forme a very large and almost complete tubular siphon on the midline
	Showing species characteristics...	Photo Seb Vasquez Reunion, Étang-Salé on the rocky coast, less 1 m, 17 June 2014

See more about : Sightening and mating periods
   See more about : Pleurobranchus grandis variability in Southwest Indian ocean

Remarks :

Identification confirmed by Bill Rudman and Nathalie Yonow
    All the specimens found in our islandsare completely dark specimen or juvenile... We need other specimens of this species to study the pattern variability.
    So, i f you have taken a photo of this species in Reunion, Mayotte or Mauritius Islands, please Contact us
    Synonymous : (according Worms)           
               - Oscanius grandis (Pease, 1868)                     
               - Pleurobranchus blainvillii Lesson, 1830                       
               - Pleurobranchus violaceus pease, 1863

Bibliographic data :

The dorsum was characterised by its division into polygonal areas , each with a very low central mound. There were smaller mounds arranged around the central one in the red areas, all separated from each other by a groove. This arrangement (Fig 6 a) was clearly visible and is characteristic of this species
Anteriorly, the mantle was deeply divided and the two lobes overlapped (Fig 6 b), enclosing the rhinophores which projected side by side though this small opening (Fig 6 c).

    A triangular pale area is present on the undersurface (pedal or metapodial gland) of the tail in sexually mature specimens
    Posteriorly, when it is crawling actively, the mantle was raised and folded to forme a very large and almost complete tubular siphon on the midline like in P. forskalii
    It feeds on compound ascidian. Although this species is generally nocturnal, sometimes adult was observed crawling on the substrate during the day.
    It lays a white spirally-arranged egg mass with one edge atached to the substrate and the other very wavy
    Juvenile has purple spots like P. forskalii and P. peroni but P. grandis has a ring of small tubercles around each of the large ones.
    It could be only confused with P. forskalii, because both are large and both raise the mantle to create temporary exhalent channels, but P. forskalii does not have its pustules arranged in groups and it invariably has a pattern of white semicircles on the mantle.

References :

Bill Rudman Seaslug site : Sea Slug Forum : Pleurobranchus grandis
   Nudipixel Pleurobranchus grandis

Publications :

Pease, W.H. (1868). Descriptions of marine Gasteropodae, inhabiting Polynesia. American Journal of Conchology, 4(2) : 71-80, Pls. 7-10.
    Yonow, N. (2000). Red sea Opistobranch 4: The orders Cephalapsidea, Anaspidea, Notaspidea and Nudibranchia: Dentronotacea and Aelidacea. Fauna of arabia 18; 87-131

Other photos of Pleurobranchus grandis :

Maurice Jay Reunion Juvenile form has purple (brown in this specimen like Erwin Koehler sp) spots, a white reticulate pattern and a ring of small tubercles around each of the large ones. See for comparaison Erwin Koehler specimen (May 2005) on Sea Slug Forum

Philibert Bidgrain chissioua sada, Mayotte, on the reef crest during a low tide , 16 0ctober 2008, size : 20-25 mm, Intermediate pattern between juvenile and adult form.

Hugues Flodrops Reunion, "La saline lagoon", less 1 m, 28 December 2007, during the night, size : 180-200 mm Posteriorly, when it is crawling actively, the mantle was raised and folded to forme a very large and almost complete tubular siphon on the midline. On the right side you can see the gills The dorsum was characterised by its division into polygonal areas (a), each with a very low central mound. There were smaller mounds arranged around the central one in the red areas, all separated from each other by a groove. This arrangement was clearly visible and is characteristic of this species Anteriorly, the mantle was deeply divided and the two lobes overlapped, enclosing the rhinophores which projected side by side though this small opening.

Philibert Bidgrain Reunion, Grand fond lagoon, Saint Gilles, less 1 m, 6 December 2009, size : 20-25 mm

See more about : Pleurobranchus grandis variability in Southwest Indian ocean

Reunion, Pleurobranchus grandis or peroni, at Etang salé, by Philibert Bidgrain

Mayotte, Pleurobranchus grandis, at M'Sapéré, by Marina Poddubetskaia 

Reunion, intermediate beetween juvenile and adult P. grandis, at Etang salé, by Christophe Cadet  

Madagascar, large Pleurobranchus grandis, at Sainte-Marie, by Myriam Dupuis

Reunion, juvenile of Pleurobranchus grandis, at Etang salé, by Nathalie Rodrigues