Opisthobranch of the Week Data
I've not personally seen Eubranchus mandapamensis in the waters of Okinawa's main island, however Atsushi Ono mentions seeing five or more individuals from the Keramas and considers the animals to be uncommon there (pers. comm.). Atsushi reports finding the above featured animal on hydroids in a sandy environment. Atsushi's photographs are used here with his kind permission.
I don't have Rao's original description (1968) of Eubranchus mandapamensis and I've taken the following description from Rudman, W.B., 2009 (May 15):
Originally described from Mandapam in south-eastern India, the characteristic external features of this species include the shape and colour of the cerata and the rhinophores.
The cerata are inflated with two rings of rounded tubercles. The original description describes grey spots all over the body and orange patches on the cerata. Also described is a 'bright yellowish orange band .. on the subapical region of the cerata, and another pink or purple-coloured band just below the subapical region'. The rhinophores are described as having 'three to five annulations at equal distance'.
Terry Gosliner suggested to me some years ago that he thought Eubranchus rubropunctatus and E. mandapamensis to be synonyms but I felt there were enough inconsistencies in Rao's description to wait until we had more information. Vishal Bhave's photos certainly match Rao's description of E. mandapamensis quite well and certainly link Edmund's description of the cerata of E. rubropunctatus with two subapical ceratal yellow bands and a bluish band with red spots between, with Rao's description of an orange band near the tip with a pink or purple-coloured band just below.
However E. rubropunctatus has distinct papillae scattered over the rhinophores while Rao clearly describes and draws evenly spaced annulations on the rhinophores. A third 'form' I have seen has smooth rhinophores [Eubranchus cf. rubropunctatus from Hong Kong].
While it is possible that one species could have this degree of rhinophoral variability I can't think of an example. At this stage I suggest we take a conservative approach and keep the three rhinophore types separate until we know more about the anatomy and variability of this species or group of species.
I've added a second page with an additional photograph of several specimens of E. mandapamensis. In addition, I've previously featured two unknown Eubranchus species on these pages, Eubranchus sp. 1, and Eubranchus sp. 2, both also photographed by Atsushi in the Keramas *.
Scott Johnson has some terrific photographs of Eubranchus mandapamensis from the Tulamben area of Bali.
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.