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

Order : Nudibranchia Suborder : Euctenidiacea Superfamily : Phyllidioidea Family : Phyllidiidae Distribution : Indo-West Pacific Oceans including the central Pacific and the Red Sea. Maximal size : 120 mm Abundance : Frequently on the fore reef zone and the reef flat zone Species characteristics : Its basic colours are black, blue-grey and yellow.    The rhinophores and rhinotubercules are yellow.    There are three to five, longitudinal, blue-grey to pale grey ridges ( broken or continuous) joining the tubercles capped in yellow.    A central ridge is always present    Towards the margins of the notum there are usually, short, transverse ridges    The foot sole possesses a black longitudinal foot stripe.
	Showing species characteristics...	Photo Christophe Cadet Reunion, Saint Pierre, 13 m, May 2009

See more about : Sightening and mating periods
   See more about : Phyllidia varicosa with a commensal shrimp ?
   See more about : Phyllidia varicosa variability in Southwest Indian ocean

Remarks :

Identification confirmed by Bill Rudman
    Synonymous (according worms) :
          - Phyllidia arabica Ehrenberg, 1831                                    - Phyllidia honloni Risbec, 1956
          - Phyllidia borbonica Cuvier, 1804                                      - Phyllidia quinquelineata Blainville, 1816
          - Phyllidia fasciolata Bergh, 1869                                       - Phyllidia trilineata Cuvier, 1804
 

Bibliographic data :

Material examined by David J.Brunckhorst ( see reference/publications).

Holotype lost; neotype (43 mm preserved lengh) in MNHN, comes from Reunion island , and was collected from 5-20 m depth, Cap la Houssaye, St Paul by J.Drivas and M.Jay in 1989.

Other external morphology characteristics

Live specimens ranged in length from 8-115 mm , average size being 57 mm.
    The rhinophores are yellow and each rhinophoral clavus possesses 27 to 30 lamellae (specimens greater than 60mm).
    The notum of Phyllidia varicosa has many conical or angular, sometimes compound tubercles with blue-grey to pale grey bases and yellow apices. There may be from three to five, longitudinal, blue-grey to pale grey ridges ( broken or continuous) joining the median tubercles.
    Towards the margins of the notum there are usually numerous, short, transverse ridges interspersed by black rays.
    The foot sole always possesses a median black longitudinal stripe which may be broken.

Other characteristics

In most dorids there is a dorsal circle of gills with the anus opening in the centre. In the phyllidiids, the circle of gills is lost, but in most cases the anus, stays in the dorsal midline, marking the spot where the gills used to be, sometimes the annal papilla is visible (see below F.Trentin photo)
    These sea slugs are masters of chemical defence. They are capable of polluting an entire aquarium if stressed in any way. They produce a pungent toxin that will kill all life in the aquarium. They have no known predators.

Similar species

Phyllidia varicosa appears to be closest to Phyllidia tula. But Phyllidia tula is known only from Micronesia and the notum possesses single rounded tubercles which are isolated and do not form ridges.
    This species has been confused with Phyllidia coelestis. P. coelestis has a broken black band down the midline and a ridge on each side of it, while in P. varicosa there is a bluish-grey ridge down the midline, with a black band on each side of it. If you can see the sole of the foot then P. varicosa has a median black line and P. coelestis does not.
    It is also likely to be mistaken for Fryeria marindica but in that species there is a single median longitudinal ridge, blue-grey in colour and it joins with coalesced tubercles, the larger ones of which are capped in yellow
    This species has been confused with Phyllidia alyta who also possesses a solid black median line on the sole of the foot. But P. varicosa has on all the rows, many yellow-capped notal tubercles ( only few and in the three inner rows in P.alyta ). P. varicosa hasn't the four caracteristics longitudinal blacklines , which are organized with a inner pair runs from behind the rhinophores to just in front of the anal papilla, and an external pair line on each side which runs from the anterior edge of the mantle back to behind the anal papilla...

References :

Bill Rudman Seaslug site : Sea Slug Forum : Phyllidia varicosa
   Nudipixel Phyllidia varicosa

Publications :

Lamarck, J.B. (1801) Systeme des animaux sans vertebres. Paris.
    Brunckhorst, D.J. (1993) The systematics and phylogeny of Phyllidiid Nudibranchs (Doridoidea). Records of the Australian Museum, Supplement 16: 1-107.

Other photos of Phyllidia varicosa :

Philibert Bidgrain Reunion, Saint Gilles, less 1 m, 18 September 2010, size : 100-110 mm   (a) The secondary gills of alI phyllidiid nudibranches are flat and triangular in shape, the longest edge being attached at right angles across the groove which occurs ventrolaterally between the mantle and the foot. (b) The foot sole always possesses a median black longitudinal stripe which may be broken.

Emmanuel Eby Rodrigues, 10 September 2004, On the roof of a cave...

You can see in this photo some of the 70-150 leaflets of the ventrolaterally gills, which are present between the mantle and the foot around the entire ventrolateral groove.

Florence Trentin Reunion, Saint Leu This specimen has a disorganisated pattern in the posterior area... Below, detail showing the dorsal anus of this nudibranch.

Florence Trentin Reunion, Diving site is "Maison verte" at Saint Leu, 20 m, 16 December 2004. Size : 40-50 mm In this specimen we can observe only a few among of yellow-capped notal tubercles

Florence Trentin Reunion, "Cap la houssaye" at Saint Paul, 12 m, 17 January 2005, size : 70-80 mm.
Upper view	The foot sole possesses a median black longitudinal stripe which may be broken

Alain Barrère Reunion, "Cap la Houssaye" at Saint Paul, 10-15 m, 20 January 2005. Begining or end of mating, between two P.varicosa...

Matthias Deuss "Nord-West reef", Mayotte, on the fore reef zone, 20m, 2 August 2009, size : 10 mm. According Nathalie Yonow : " This seaslug is a juvenile of P. varicosa ", the adult pattern is not fully developed. This specimen looks like Fryeria marindica with a median ridge with a single row of coalescent yellow capped tubercles.

Matthias Deuss Mayotte, buoy 4 from Passe en S , 15 m, 23 December 2009, size : 10 mm. Another juvenile form of P. varicosa... This specimen looks like Fryeria marindica with a median ridge with a single row of coalescent yellow capped tubercles.

Philibert Bidgrain Mayotte, Gombé Ndroumé, less 1 m, 21 December 2011, size : 30-40 mm A specimen with large transverse black ridges towards the margins of the notum.

See more about : Phyllidia varicosa with a commensal shrimp ?
   See more about : Phyllidia varicosa variability in Southwest Indian ocean
   Mauritius, Phyllidia varicosa, at , by Mathieu Bayon
   Rodrigues, Phyllidia varicosa spawn, at Mourouk, by Alain Martinat  
   Mayotte, Phyllidia varicosa, at mtsanga Chéhi, by Philibert Bidgrain 
   Mayotte, Phyllidia varicosa with retracted rhinophore, at Hajangua, by Matthias Deuss
   Mayotte, Phyllidia varicosa, by Norbert Verneau  
   Mayotte, Phyllidia varicosa with a few among of yellow-capped tubercles, at Nord-West reef, by Matthias Deuss
   Mayotte, juvenile form of Phyllidia varicosa, by Sylvain Le Bris 
   Rodrigues, Phyllidia varicosa with numerous yellow/orange tubercles, at Saint François, by Thierry Peres  
   Reunion, Phyllidia varicosa, at La Saline, by Philibert Bidgrain
   Madagascar, Phyllidia varicosa at Nosy Iranja, by Hugues Flodrops
   Seychelles, Phyllidia varicosa with numerous yellow/orange tubercles, at Mahé, by Christophe Mason-Parker
   Madagascar, strange meeting between P. exquisita and P. varicosa, at Nosy Bé, by Alain-Benoît Rassat