May 12, 2005
From: Bill Rudman
The identity of the small sea hares of the genera Phyllaplysia and Petalifera is very confused and as many species are based on descriptions of preserved animals, or simply described as 'green', we will probably never be able to resolve all the older names. The situation is also confused by many authors considering that species of Phyllaplysia lacked a shell while those of Petalifera possessed one. This confusion is very well illustrated by the species found in the Mediterranean. Some recent messages have forced me to revisit the question of just what is the difference between Petalifera petalifera and Phyllaplysia lafonti.
The original description of Petalifera petalifera is not easy to interpret, but most authors have accepted it to apply to a reasonably common, small translucent sea hare covered in an irregular pattern of brown to green patches and diffuse spots. It has been reviewed and illustrated by Fasulo et al (1984) and Terreni (1997).
Phyllaplysia lafonti was originally described from the Baie d'Arcachon on the Atlantic coast of France. Like all species of Phyllaplysia and Petalifera it is described as small, flattened, and with very reduced parapodia. The colour is described as very variable, but one distinctive feature of the written desription and the accompanying drawing are the way the body consists of concentric bands ['zones concentriques'] of lighter and darker pigmentation. Also described are whitish spots ringed with purple. Fischer was unable to determine whether there was a shell but Terreni (1997) illustrates a relatively large fragile internal shell. It is hard to be sure which of the earlier references to this species in the Mediterranean are actually correct, but there are some good colour photos of correctly identified Phyllaplysia lafonti in an article by Terreni (1997) in La Conchiglia. In this article he compares it with Petalifera petalifera.
In the literature both these species have been identified as Petalifera petalifera and I have previously followed that in the Forum. I have moved the following messages previously identified as P. petalifera to P. lafonti, giving that species a wide distribution in theIndo-West Pacific as well as the eastern Atlantic [messages #9017, #5433].
Fasulo, G., Izzillo, F., Russo, G. F., Toscano, F., and Villani, G. (1984) Nota su Petalifera petalifera (Rang, 1828) (Gastropoda, Opisthobranchia, Aplysiomorpha), specie Mediterranea poco conosciuta. Considerazioni sistematiche, ecologiche e biogeografiche. Bollettino Malacologico, 20: 263-272.
Fischer, P (1870) Observations sur les Aplysies. Ann. de Sci. Nat (5). Zool & Pal, 13: 3
Fischer, P (1872) Description d'une espece nouvelle du genre Phyllaplysia. Journal de Conchyliologie, 20: 295-301.
Martinez, E. (1996) On Petalifera petalifera (Rang, 1928) (Gastropoda: Opisthobranchia): new anatomical and geographical data. Journal of Molluscan Studies, 62: 243-250.
Rang, S. (1828) Histoire naturelle des Aplysiens, premiere famille de l'ordre des Tectibranches. In: Histoire naturelle Generale et particuliere des Mollusques. Firmin Didot, Paris, 84pp. Pls. 1-24.
Terreni, G. (1997) Rinvenimento di un esemplare di Phyllaplysia lafonti (P. Fischer, 1870) nelle acque litorali di Livorno (Gastropoda, Opisthobranchia, Aplysiomorpha). La Conchiglia, Roma, 29 (282): 45-47.