Another Step Towards Understanding the Slit-Limpets (Fissurellidae, Fissurelloidea, Vetigastropoda, Gastropoda): A Combined Five-Gene Molecular Phylogeny

Abstract

Fissurellids, commonly known as slit or keyhole limpets, are limpet-shaped gastropods that typically possess a hole, slit or notch in their bilaterally symmetrical shells and usually occur on rocky marine substrates. Competing classifications for Fissurellidae have been circumscribed using various morphological characters such as radular, shell and mantle features; two to five different subfamilies have been recognized. Although fissurellid species are frequently included in larger vetigastropod phylogenies, relatively few phylogenetic studies of the group have been performed. This study presents a phylogenetic investigation of the relationships amongst slit-limpets in the vetigastropod superfamily Fissurelloidea, representing the first molecular phylogeny of this clade. In this study, the monophyly of Fissurelloidea and Fissurellidae varied depending on the analytical method used, but clades compatible with the subfamilies Diodorinae and Fissurellinae were recovered with high bootstrap support in all analyses. Species traditionally classified in Emarginulinae formed two groups identified in this study as Hemitominae (Puncturella, Cranopsis and Hemitoma) and Emarginulinae sensu stricto (Emarginula, Montfortula, Tugali, Scutus and Nannoscutum), but Hemitominae was only monophyletic in the maximum likelihood analysis. The results of this study contradict traditional fissurellid classifications as well as theories about the evolution of key fissurellid shell characters. The placement of Puncturella, Cranopsis and Hemitoma sister to all remaining fissurellids suggests that the presence of an anteriorly placed foramen or notch is plesiomorphic, and that an anterior notch or slit evolved multiple times in Fissurellidae.