[Paleontology • 2015]
A Vanished History of Skeletonization in Cambrian Comb Jellies (Ctenophora)
Ctenophores are traditionally regarded as “lower” metazoans, sharing with cnidarians a diploblastic grade of organization. Unlike cnidarians, where skeletonization (biomineralization and sclerotization) evolved repeatedly among ecologically important taxa (for example, scleractinians and octocorals), living ctenophores are characteristically soft-bodied animals. We report six sclerotized and armored ctenophores from the early Cambrian period. They have diagnostic ctenophore features (for example, an octamerous symmetry, oral-aboral axis, aboral sense organ, and octaradially arranged ctene rows).
Unlike most modern counterparts, however, they lack tentacles, have a sclerotized framework, and have eight pairs of ctene rows. They are resolved as a monophyletic group (Scleroctenophora new class) within the ctenophores. This clade reveals a cryptic history and sheds new light on the early evolution of this basal animal phylum. Skeletonization also occurs in some other Cambrian animal groups whose extant members are exclusively soft-bodied, suggesting the ecological importance of skeletonization in the Cambrian explosion.
Keywords: Cambrian, Chengjiang biota, Ctenophora, skeleton
Qiang Ou, Shuhai Xiao, Jian Han, Ge Sun, Fang Zhang, Zhifei Zhang and Degan Shu. 2015. A Vanished History of Skeletonization in Cambrian Comb Jellies. Science Advances. 1(6); e1500092. DOI: 10.1126/sciadv.1500092