Data from: 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 but
with a typical molluscan radula and serially repeated gills. In order to
better resolve the relationships among molluscs we generated transcriptome
data for 15 molluscs that, in combination with existing data, represent
for the first time all major molluscan groups. We analysed multiple data
sets containing up to 216,402 sites and 1185 gene regions using multiple
models and methods. Our results support a clade Aculifera, containing the
three molluscan groups with spicules but without true shells, as well as
the monophyly of Conchifera—the shelled molluscs. Monoplacophora are not
the sister group to other Conchifera, but constitute the sister group to
the highly modified cephalopods. Strong support is found for a clade
comprised of Scaphopoda (tusk shells), Gastropoda, and Bivalvia, with most
analyses placing Scaphopoda and Gastropoda as sister groups. This
well-resolved tree will constitute a framework for further studies in
mollusc evolution, development and anatomy.