Sebadoris fragilis ( Alder and Hancock, 1864 )

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


Order : Nudibranchia
Suborder : Euctenidiacea
Superfamily : Doridoidea
Family : Discodorididae
Distribution : Indo-Western Pacific
Maximal size : 120 mm
Abundance : Seldom on the reef flat zone

Species characteristics :

The overall appearance is greyish brown, but the colour on the mantle is really a complex mottling of pale brown, chocolate, or greenish brown and cream.
   There are large dark brown spots in pairs mid-dorsally and also, two or three white patches in the dorsal midline.
    The edge of the mantle, which is paler than the rest, has some dark brown spots.
    Mantle firm and rough to the touch. Dorsum covered by numerous, small conical tubercles, which are larger near the central area.

Discodoris fragilis
Showing species characteristics...
Photo Delphine Dupin
Reunion, "Petit trou d'eau" at l'Hermitage, 1 May 2005, size : 40 to 50 mm

See more about : Sightening and mating periods
   See more about : Sebadoris fragilis variability in Southwest Indian ocean

Remarks :

Identification confirmed by Bill Rudman and Nathalie Yonow
    The identification of this species seems to be very variable in different books and web site... I decided to use the term of Sebadoris fragilis for this kind of specimens, but I'm not sure of that...
    Synonymous (according worms) :
          - Alloiodoris hedleyi, O'Donoghue, 1924                           - Doris sordida, Rüppell & Leuckart, 1830
          - Discodoris fragilis, (Alder & Hancock, 1864)                   - Doris sordidata, Abraham, 1877
          - Discodoris morphaea, Bergh, 1877                               - Doris stragulata, Abraham, 1877
          - Discodoris notiperda, Risbec, 1956
          - Discodoris vanikoro, Pruvot-Fol, 1934
          - Doris fragilis, Alder & Hancock, 1864
          - Doris granulata, Ehrenberg, 1831

Bibliographic data :

For some authors Tayuva lilacina (Gould, 1852), Sebadoris fragilis (Alder and Hancock, 1864) Discodoris concinna (Alder and Hancock, 1864) and Discodoris concinniformis ( Bergh, 1888) are probably the same species and in that case the name is Tayuva lilacina (Gould, 1852). For other authors they are different species. Until we have a better idea as to whether we are dealing with one widespread variable species or a number of very similar looking species, the taxonomy will remain confused and which evolves, will take into account in this page of the results of Dayrat, 2010
    The undersurface of the mantle is pale grey with large chocolate brown blotches, especially adjacent to the narrow foot. The foot sole is densely brown speckled.
    The five or six moderately small, compound gills are fawnish brown with white tips and form a complete circle around the anus.
    The rhinophores are brown with a white streak up the posterior face and white speckling on the lamellae.
    S. fragilis can deliberately break off (autotomise) large pieces of its mantle margin when it is irritated and this is accompanied by the production of great quantities of clear mucus.
    It feeds on siliceous sponges (desmospongia) like Callyspongia diffusa
    The spawn forms a wide and flat coiled egg ribbon, of 2-4 coils, up to 80 mm in diameter
    S. fragilis could be mistaken for Sebadoris nubilosa, but that is much larger, its mantle bears large soft conical papillae all over its surface, and it can swim when it is disturbed.
    The dark form of Sebadoris fragilis may be confused with Asteronotus raripilosus but A. raripilosus has branched dorsal papillae and a six lobed branchial sheath that are absent in S. fragilis

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

Two specimens collected from Grand Baie (Mauritius), 2 November 1985, size : 73 and 84 mm.

References :

Bill Rudman Seaslug site : Sea Slug Forum : Discodoris lilacina
   Nudipixel Discodoris fragilis

Publications :

Alder, J & Hankock. A, 1864. Notice of a collection of nudibranchiate mollusks made in India by Walter Elliot, Esq., with descriptions of some new genera and species. Transactions of the Zoological Society of London , 5: 113-147. pls 28-33
    Bloom, S. A. 1976. Morphological correlations between dorid nudibranch predators and sponge prey. Veliger 18(3):289-301.
    Dayrat B. (2010). A monographic revision of basal discodorid sea slugs (Gastropoda, Opisthobranchia, Nudibranchia, Doridina). Proceedings of the California Academy of Sciences. Series 4, vol. 61, suppl. I, 1-403, 382 figs.
page(s): 139-174
    Gould, A.A. (1852). United States Exploring Expedition during the Years 1838-1842. Mollusca & Shells, 12 : 1-510. (with Atlas of Plates, 1856).
    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
    Young, D. K. 1966. Systematics, food and functional morphology of the feeding apparatus of some dorid nudibranchs. Ph.D. Dissertation, Univ. Hawaii

Other photos of Sebadoris fragilis :


Philippe Bourjon

Reunion, less 1 m, 2 April, 2016

A strange pattern for this specimen...

 

 


Sébastien Vasquez

Reunion, Etang sale on the rocky coast, less 1 m, 20 March 2015,

 




Jean-Marie Gradot

Reunion, Etang salé on the rocky coast, less 1m,13 December 2015

 

 


Delphine Dupin
Reunion, "Petit trou d'eau" at l'Hermitage,, 1 May 2005, 40 to 50 mm

The rhinophores are brown with a white streak up the posterior face and white speckling on the lamellae.

Dorsum covered by numerous, small conical tubercles, which are larger near the central area.

The five or six moderately small, compound gills are fawnish brown with white tips and form a complete circle around the anus.




Philibert Bidgrain

A spawning event. I find this specimen which spawn under a rock during rhe day...

Reunion, Etang salé lagoon, less 1m, 9 November 2008, size : 70-80mm

The undersurface of the mantle is pale grey with large chocolate brown blotches, especially adjacent to the narrow foot.


Maurice Jay

Reunion, Saint Leu and Trou d'eau lagoon, under rocks, size : 45 mm

A darker form of S. fragilis.


Philibert Bidgrain

mtsanga Guini, Mayotte, less 1 m, on the reef flat area, 29 Jully 2008, size : 40-50 mm

The undersurface of the mantle is pale grey with large chocolate brown blotches, especially adjacent to the narrow foot. The foot sole is densely brown speckled.


 More photos from Indian Ocean

See more about : Sebadoris fragilis variability in Southwest Indian ocean

Mauritius, drawing of a specimen of Discodoris fragilis, from Grand Baie, by Nathalie Yonow

Reunion, underside and foot sole of Discodoris fragilis, at Etang salé, by Christophe Cadet  

Reunion, underside and foot sole of Discodoris fragilis, at Saint Gilles, by Philippe Bourjon  

Reunion, underside and foot sole of Discodoris fragilis, at Etang salé, by Philibert Bidgrain

Reunion, Discodoris fragilis crawling on a sea urchin, at Etang salé, by Matthias Deuss  

Mauritius, Discodoris fragilis with large dark brown spots on the notum, at Riviére noire, by Hilary Jones