Exotic cuticular specializations in a Cambrian scalidophoran.

Abstract

Scalidophora, the ecdysozoan group including priapulids, kinorhynchs and loriciferans, comprises some of the most abundant and ecologically important Cambrian animals. However, reconstructions of the morphology and lifestyles of fossil scalidophorans are often hampered by poor preservation of their submillimetre-scale cuticular specializations. Based on exceptionally preserved small carbonaceous fossils (SCFs), we describe a new scalidophoran-grade animal, Scalidodendron crypticum gen. et sp. nov., from the Early to Middle Cambrian Hess River Formation of northern Canada. The Hess River SCFs comprise pharyngeal teeth, coniform sclerites and hook-like sclerites, all closely comparable to known scalidophoran counterparts. The coniform and hook-like sclerites recurrently associate with arborescent cuticular projections that show multiple orders of branching, morphologically unlike those of any known living or fossil scalidophoran. The fine splintering and inferred post-pharyngeal position of these structures argue against locomotory, feeding and defensive roles with direct analogues in extant counterparts. As such, the arborescent structures of Scalidodendron denote a previously cryptic range of morphological variation in Cambrian scalidophorans, paralleling that of coeval panarthropods but expressed at a fundamentally different level of anatomical organization.