Data from: A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan

Reconstructing the evolutionary assembly of animal body plans is
challenging when there are large morphological gaps between extant sister
taxa, as in the case of echinozoans (echinoids and holothurians). However,
the inclusion of extinct taxa can help bridge these gaps. Here we describe
a new species of echinozoan, Sollasina cthulhu, from the Silurian
Herefordshire Lagerstätte, UK. S. cthulhu belongs to the ophiocistioids,
an extinct group that shares characters with both echinoids and
holothurians. Using physical-optical tomography and computer
reconstruction, we visualize the internal anatomy of S. cthulhu in three
dimensions, revealing inner soft tissues that we interpret as the ring
canal, a key part of the water vascular system that was previously unknown
in fossil echinozoans. Phylogenetic analyses strongly suggest that
Sollasina and other ophiocistioids represent a paraphyletic group of stem
holothurians, as previously hypothesized. This allows us to reconstruct
the stepwise reduction of the skeleton during the assembly of the
holothurian body plan, which may have been controlled by changes in the
expression of biomineralization genes.