Consolidated data on the phylogeny and evolution of the family Tritoniidae (Gastropoda: Nudibranchia) contribute to genera reassessment and clarify the taxonomic status of the neuroscience models Tritonia and Tochuina

Abstract

Nudibranch molluscs of the family Tritoniidae are widely used neuroscience model systems for understand the behavioural and genetic bases of learning and memory. However species identity and genus-level taxonomic assignment of the tritoniids remain contested. Herein we present a taxonomic review of the family Tritoniidae using integration of molecular phylogenetic analysis, morphological and biogeographical data. For the first time the identity of the model speciesTritonia tetraquetra(Pallas, 1788) andTritonia exsulansBergh, 1894 is confirmed.T.tetraquetradistributes across the large geographic and bathymetric distances in the North-Eastern (NE) and North-Western (NW) Pacific. In turn, at NE Pacific coasts the separate speciesT.exsulansis commonly occured. Thus, it reveals a misidentification ofT.tetraquetraandT.exsulansspecies in neuroscience applications. Presence of more hidden lineages within NW PacificT.tetraquetrais suggested. The long lasting confusion over identity of the species from the generaTritoniaandTochuinais resolved using molecular and morphological data. We also disprove a common indication about “edibleT.tetraquetra” at the Kuril Islands. It is shown thatTochuinapossesses specialized tritoniid features and also some characters of “arminacean nudibranchs”, such asDoridoxaandHeterodoris. Diagnoses for the families Doridoxidae and Heterodorididae are provided. Taxonomy of the genusDoridoxais clarified and molecular data for the genusHeterodorispresented for the first time. A taxonomic synopsis for the family Tritoniidae is provided. A new genus among tritoniid taxa is proposed. Importance of the ontogeny-based taxonomy is highlighted. The cases when apomorphic characters considerably modified in a crown group due to the paedomorphosis are revealed. Tracing of the character evolution is presented for secondary gills–a key external feature of the family Tritoniidae and traditional dendronotacean nudibranchs.