Ultraconserved element-based phylogenomics and siphonal traits illuminate the evolution of tellinoidean clams (Mollusca: Bivalvia: Tellinoidea)

Abstract Tellinoidea, one of the most diverse superfamilies of Bivalvia, include 954 extant species classified into five families. Although the monophyly of Tellinoidea is well corroborated by morphological and molecular data, the monophyly of the individual families and their relationships remain contentious, hampering further macroevolutionary studies. By using an ultraconserved element probe set recently developed for the class Bivalvia, we captured 825 ultraconserved elements from 33 fresh and historical museum specimens and produced a phylogeny for Tellinoidea with strong support for its internal relationships. Our analyses recovered Donacidae as monophyletic, whereas Solecurtidae were inferred as paraphyletic, and Psammobiidae, Semelidae, and Tellinidae were resolved as polyphyletic lineages. The results reinforce the need for reassessment of these families, because phylogenetic evidence suggests, for example, that semelids and the genus Sanguinolaria are nested within Tellinidae. Leveraging this phylogenetic framework, we estimated ancestral states of four key traits: burrowing depth, feeding habit, tentacle form, and the number of siphonal tentacles in the incurrent aperture. Our results show lineage-specific variations of the siphon anatomy and specialization for deposit-feeding behaviour. Overall, we also highlight evolutionary convergences and discuss potential scenarios for the diversification of tellinoids in shallow-water environments.