Frogs and tuns and tritons – A molecular phylogeny and revised family classification of the predatory gastropod superfamily Tonnoidea (Caenogastropoda)

Abstract

The Tonnoidea is a moderately diverse group of large, predatory gastropods with ∼360 valid species. Known for their ability to secrete sulfuric acid, they use it to prey on a diversity of invertebrates, primarily echinoderms. Tonnoideans currently are classified in seven accepted families: the comparatively well known, shallow water Bursidae, Cassidae, Personidae, Ranellidae, and Tonnidae, and the lesser-known, deep water Laubierinidae and Pisanianuridae. We assembled a mitochondrial and nuclear gene (COI, 16S, 12S, 28S) dataset for ∼80 species and 38 genera currently recognized as valid. Bayesian analysis of the concatenated dataset recovered a monophyletic Tonnoidea, with Ficus as its sister group. Unexpectedly, Thalassocyon, currently classified in the Ficidae, was nested within the ingroup as the sister group to Distorsionella. Among currently recognized families, Tonnidae, Cassidae, Bursidae and Personidae were supported as monophyletic but the Ranellidae and Ranellinae were not, with Cymatiinae, Ranella and Charonia supported as three unrelated clades. The Laubierinidae and Pisanianuridae together form a monophyletic group. Although not all currently accepted genera have been included in the analysis, the new phylogeny is sufficiently robust and stable to the inclusion/exclusion of nonconserved regions to establish a revised family-level classification with nine families: Bursidae, Cassidae, Charoniidae, Cymatiidae, Laubierinidae, Personidae, Ranellidae, Thalassocyonidae and Tonnidae. The results reveal that many genera as presently circumscribed are para- or polyphyletic and, in some cases support the rescue of several genus-group names from synonymy (Austrosassia, Austrotriton, Laminilabrum, Lampadopsis, Personella, Proxicharonia, Tritonoranella) or conversely, support their synonymization (Biplex with Gyrineum). Several species complexes are also revealed that merit further investigation (e.g., Personidae: Distorsio decipiens, D. reticularis; Bursidae: Bursa tuberosissima; Cassidae: Echinophoria wyvillei, Galeodea bituminata, and Semicassis bisulcata). Consequently, despite their teleplanic larvae, the apparently circumglobal distribution of some tonnoidean species is the result of excessive synonymy. The superfamily is estimated to have diverged during the early Jurassic (∼186 Ma), with most families originating during a narrow ∼20 My window in Albian-Aptian times as part of the Mesozoic Marine Revolution.