An interpretation of the taxonomic relationship between the limpets Patella rustica and P-piperata

The taxonomic relationship between the limpets Patella rustica (Mollusca: Archaeogastropoda) and P. piperata is unclear with controversy as to whether P. piperata should be given specific status. The problems stem from its similar morphology but different biogeographic range from P. rustica. Individuals from seven populations of P. rustica and three of P. piperata were analysed for a combination of morphological and genetical characters. Morphological analyses of shell shape and radular morphology revealed differences between species for radular length, higher in P. rustica than in P. piperata, and the shape of the pluricuspid teeth of the radula with a well-developed internal cusp in P. piperata but not in P. rustica. Electrophoretic results based on 11 allozyme loci, however, did not distinguish the two species clearly. The overall genetic identity value between the two was 0.861, a value which lies within the range for conspecific populations of other patellids. It is proposed that P. piperata on the basis of the genetic data obtained, may represent a subspecies of P. rustica that is in the process of diverging due to its geographic isolation.