Microstructure of the Plates in the Carpoid Echinoderm Paranacystis

Study of the microstructure of the plates of the Lower Devonian carpoid Paranacystis from Paraná, Brazil, indicates that they were penetrated by a labyrinth of fine canals which continued from plate to plate and opened on the outer surface in minute pores. The structure is similar to that described in the outer layer of plates of the ostracoderm Procephalaspis oeselensis. It is suggested that, if the carpoids and ostracoderms are directly related, it is possible the canals originally functioning in respiration eventually came to possess sensory receptors.