Recently we documented a bilaterally symmetrical, solitary organism, Yanjiahella biscarpa from the early Cambrian (Fortunian) of China¹. We interpreted that Y. biscarpa possessed an echinoderm-like plated theca, a muscular stalk similar to hemichordates and a pair of long, feeding appendages. Our interpretation and our phylogenetic analysis suggest that Y. biscarpa is a stem-echinoderm, which would confirm that echinoderms acquired plates before pentaradial symmetry and that their history is firmly rooted in bilateral forms. Zamora et al.² however, have criticized our interpretation, arguing against an echinoderm affinity, instead suggesting that the phylogenetic placement of Y. biscarpa is dubious and its significance for understanding deuterostome evolution is uncertain.

This criticism² seems to stem from our interpretation of particular morphological features in Y. biscarpa¹ and the perceived lack of echinoderm synapomorphies. Echinoderms possess a calcitic skeleton with a distinctive three-dimensional mesh-like microstructure called stereom, that is considered a major synapomorphy of the Echinodermata³. Zamora et al.² highlighted the absence of stereom in Y. biscarpa, additionally stating that we had omitted appropriate methods, specifically latex casting, that may confirm the presence of stereom in our specimens. We concede that initially we did not latex cast any specimens of Y. biscarpa, predominantly due to the fragile nature and the associated risk of damaging the specimens in question. In lieu of latex casting we employed Scanning Electron Microscopy (SEM) to investigate the surface and the details of Y. biscarpa specimens. SEM has been extensively used in the past to study stereom microstructure^4,5,6 and if such a microstructure was preserved in Y. biscarpa it would have been detected using this technique.