Stalked eocrinoids attached onto hyolithids with helens from Cambrian Kaili Formation in Jianhe, Guizhou, South China

Reliable fossil record regarding symbiotic relationship is a key to understanding the ecology and environment in Cambrian. Herein, we exhibited an exceptionally well preserved hyolithid with intact stalked eocrinoids attaching on the operculum and conch venter, indicating the symbiotic relationship between hyolithids and eocrinoids. By that we carried out a reconstruction for their epibiotic relationship on the Cambrian sea floor. The ontogenetic features of two eocrinoids on the operculum indicated they were immature (in the early stage of ontogeny). And considering the correlation between the orientation of eocrinoids and the mud flow in event-induced rapid burial, we proposed the orientation of eocrinoids implies the direction of mud flow. Addition-ally, based on specimens with signs of transport, we found that taphonomical factors besides ecological factors could also lead eocrinoids to preferentially attach on the dorsal or dorso-lateral surface of the conch, which was usually interpreted as a mutualism in previous reports though.