The morphology of Patella spp. juveniles in Britain, and some phylogenetic inferences

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Abstract
Juveniles of Patella spp. in Britain are shown to be easier to classify than adults, on shell morphology alone, because of a species-specific difference in number and arrangement of the post-larval mantle tentacles. The limpets can thus be clearly divided into three distinct spp.: P. vulgata Linn., 1758, P. aspera Roding, 1798, and P. depressa Pennant, 1777, which confirms recent evidence from gel-electrophoreric studies. As the limpet grows, this initial difference gives rise to many of the variables of shell shape and colour upon which adult identification is based. In the process, it can be influenced by environmental factors to the extent of producing confusing phenotypes such as those hitherto supposed to be hybrid or genetically transitional forms. The characters described suggest that, contrary to current opinion, P. aspera and P. depressa are related more closely to each other than to P. vulgata; they may also have some bearing on the species' success and distribution in the British Isles.