Resolving the evolutionary relationships of molluscs with phylogenomic tools

Molluscs (snails, octopuses, clams, and relatives) have great body plan disparity, and among animals only arthropods surpass them in species number. This diversity has made Mollusca one of the best-studied groups of animals, yet their evolutionary relationships remain poorly resolved. Open questions have important implications for the origin of Mollusca and morphological evolution within the group. These include whether the shell-less vermiform aplacophoran molluscs diverged prior to the origin of the shelled molluscs (Conchifera), or secondarily lost their shell. Monoplacophora were not included in molecular studies until recently , when it was proposed that they constitute a clade with chitons named Serialia, reflecting the serial repetition of body organs in both groups. Attempts to understand the early evolution of molluscs become even more complex when considering the large diversity of Cambrian fossils. These can have multiple dorsal shell plates and sclerites, or be shell-less bu...