Molecular phylogenetics of Caenogastropoda (Gastropoda: Mollusca).

Caenogastropoda is the dominant group of marine gastropods in terms of species numbers, diversity of habit and habitat and ecological importance. This paper reports the first comprehensive multi-gene phylogenetic study of the group. Data were collected from up to six genes comprising parts of 18S rRNA, 28S rRNA (five segments), 12S rRNA, cytochrome c oxidase subunit I, histone H3 and elongation factor 1alpha. The alignment has a combined length of 3995 base positions for 36 taxa, comprising 29 Caenogastropoda representing all of its major lineages and seven outgroups. Maximum parsimony, maximum likelihood and Bayesian analyses were conducted. The results generally support monophyly of Caenogastropoda and Hypsogastropoda (Caenogastropoda excepting Architaenioglossa, Cerithioidea and Campanilioidea). Within Hypsogastropoda, maximum likelihood and Bayesian analyses identified a near basal clade of nine or 10 families lacking an anterior inhalant siphon, and Cerithiopsidae s.l. (representing Triphoroidea), where the siphon is probably derived independently from other Hypsogastropoda. The asiphonate family Eatoniellidae was usually included in the clade but was removed in one Bayesian analysis. Of the two other studied families lacking a siphon, the limpet-shaped Calyptraeidae was associated with this group in some analyses, but the tent-shaped Xenophoridae was generally associated with the siphonate Strombidae. The other studied hypsogastropods with an anterior inhalant siphon include nine families, six of which are Neogastropoda, the only traditional caenogastropod group above the superfamily-level with strong morphological support. The hypotheses that Neogastropoda are monophyletic and that the group occupies a derived position within Hypsogastropoda are both contradicted, but weakly, by the molecular analyses. Despite the addition of large amounts of new molecular data, many caenogastropod lineages remain poorly resolved or unresolved in the present analyses, possibly due to a rapid radiation of the Hypsogastropoda following the Permian-Triassic extinction during the early Mesozoic.