Characterization and multivariate analysis of Patella intermedia, Patella ulyssiponensis and Patella vulgata from Póvoa de Varzim (Northwest Portugal)

Samples of Patella intermedia, Patella ulyssiponensis and Patella vulgata were collected from the lowest to the highest level of A Ver-o-Mar and Aguçadoura beaches (Póvoa de Varzim, Portugal). Identification of the specimens was based on the morphology of the radula pluricuspid teeth and of the shell. Regressions of shell width or shell apexpos vs. shell length yielded slopes not statistically different, but slopes of log shell height vs. shell length regression lines were significantly different, indicating that these limpets have different shell growing patterns. However, canonical discriminant analyses using only variables describing shell form yielded poor discrimination between species. Analysis using only variables describing radula relative size improved discrimination, was very satisfactory for P. ulyssiponensis specimens, but resulted in a low identification of P. intermedia. The best results were achieved using both shell form and radula relative size variables, and the most discriminating variable was radula length/shell height ratio, instead of radula length/shell length as reported in the literature. However, whereas correct identification of P. ulyssiponensis specimens was very good (higher than 95 %), for P. intermedia and P. vulgata, this value ranged from 70 – 80 %. In light of data reported in the literature, morphometric characteristics such as those utilized in this work are probably useful for characterization of P. ulyssiponensis as a species, but are of limited value for P. intermedia and P. vulgata. Qualitative characters are thus still indispensable for the discrimination between these two Patella species. Very good qualitative discriminators were, for P. intermedia, the tall and broad cusp 2 and the dark marginal rays in the shell interior surface, and for P. vulgata, the pointed protuberance on cusp 3, and the silvery head scar.