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   Marianina rosea (Pruvot-Fol, 1930)                              
         Rosy Nudibranch                                                                                                     
         Elisha Simpson (2013)                

Fact Sheet



Physical Description


Life History & Behaviour

Anatomy & Physiology (Research project)

Evolution & Systematics

Biogeographic Distribution

Conservation & Threats

References & Links

Evolution & Systematics

Detorsion has allowed for the evolution and specialisation of the Opisthobranch body plan. As the chitinous shell was gradually lost, the animal evolved a larger body size, became more elaborate in its design and bright colouration. Through this process the positioning of the mantle cavity and organs have relocated from above the head downwards alongside the right side of the body towards the posterior end of the animal (Rudman 2000).  

There has been considerable confusion surrounding the classification of Marianina rosea. Initially, this species of nudibranch was placed under the infraorder Dendronotina and further positioned into the family Tritoniidae (Pruvot-Fol,1930). It was placed in with the Tritoniids on the basis that M. rosea displayed a soft, elongate body with the edge of the mantle bearing a series of branched cerata that are lined in pairs, and contain secondary respiratory gills. Upon re-evaluation of the taxonomy of Tritoniids, Odhner (1936) relocated M. rosea into its own separate family, Marininidae or its synonym Aranucidae. Odhner (1936) renamed Marianina rosea as Aranucus bifidus on the basis of the separation of the right and left digestive glands.

Specimens of M.rosea are also often mistaken for Aeolids due to similarities in anatomical features. Upon further inspection of the species, the distinctive bright blood-red palmate rhinophoral clavi with their tubular sheaths are representative of the physiological features belonging to the family Tritoniidae (Marhsall &Willan, 1999)(Willan 1988). Willan (1988) suggests that M. rosea is the most primitive form of a Tritoniid nudibranch, that has undergone further 'Aeolidization' than its Tritoniid members.

Alice Pruvot-Fol classification of Marianina rosea (1930):

Kingdom: Animalia                                            
Phylum: Mollusca                                            
Class: Gastropoda                                                     
Subclass: Heterobranchia                                            
Infraclass: Opisthobranchia                                                     
Order: Nudibranchia                                                     
Suborder: Dexiarchia                                                     
Infraorder: Dendronotida                          
Superfamily: Tritonioidea                                                     
Family: Tritoniidae                                                              
Genus: Marianina                                                     
Species: Marianina rosea                                                                                                           

Odhner classification of Marianinarosea (Aranucus bifidus) (1936):

Kingdom: Animalia                  
Phylum: Mollusca                  
Class: Gastropoda                  
Subclass: Heterobranchia                  
Infraclass: Opisthobranchia                  
Order: Nudibranchia                  
Suborder: Dexiarchia                  
Infraorder: Dendronotida                  
Family: Aranucidae(Marianinidae)                  
Genus: Aranucus                  
Species: Aranucus bifidus

Recent taxonomy from Pola and Gosliner (2010) has now confirmed, through molecular phylogeny, that M. rosea does in fact belong to the family Tritoniidae. Through sequencing of two mitochondrial (cytochrome c oxidase subunit 1, and 16S rRNA) and one nuclear gene (Histone 3) Pola and Gosliner were able to confirm that suborders Bornellidae and Dendronotidae are now monophyletic. This resulted in M. rosea being transferred from the separate family Aranucidae back into Tritoniidae, which is now the widely accepted classification of Marianina rosea. The exact cladogram of Marianina rosea can be found in the publication by Pola and Gosliner (2010).