Data from: Developmental biology of the early Cambrian cnidarian Olivooides

Fossilized embryos afford direct insight into the pattern of development
in extinct organisms, providing unique tests of hypotheses of
developmental evolution based in comparative embryology. However, these
fossils can only be effective in this role if their embryology and
phylogenetic affinities are well constrained. We elucidate and interpret
the development of Olivooides from embryonic and adult stages and use
these data to discriminate among competing interpretations of their
anatomy and affinity. The embryology of Olivooides is principally
characterized by the development of an ornamented periderm that initially
forms externally and is subsequently formed internally, released at the
aperture, facilitating the direct development of the embryo into an adult
theca. Internal anatomy is known only from embryonic stages, revealing two
internal tissue layers, the innermost of which is developed into three
transversally arranged walls that partly divide the lumen into an
abapertural region, interpreted as the gut of a polyp, and an adapertural
region that includes structures that resemble the peridermal teeth of
coronate scyphozoans. The anatomy and pattern of development exhibited by
Olivooides appears common to the other known genus of olivooid,
Quadrapyrgites, which differs in its tetraradial, as opposed to
pentaradial symmetry. We reject previous interpretations of the olivooids
as cycloneuralians, principally on the grounds that they lack a through
gut and introvert, in embryo and adult. Instead we consider the affinities
of the olivooids among medusozoan cnidarians; our phylogenetic analysis
supports their classification as total-group Coronata, within
crown-Scyphozoa. Olivooides and Quadrapyrgites evidence a broader range of
life history strategies and bodyplan symmetry than is otherwise commonly
represented in extant Scyphozoa specifically, and Cnidaria more generally.