ABSTRACT
Cornute and mitrate carpoids are enigmatic, extinct echinoderms whose phylogenetic relationships, functional morphology, and life modes have been subjects of much debate. Because neither mouth nor anus can be identified with certainty, there is no general agreement on even the basic elements of orientation. Life modes were distinct in the cornutes and mitrates. Evidence for a sluggish epifaunal life habit in the cornutes is seen in the flattened asymmetrical body, the presence of downward projecting spines and knobs on the marginals in many species, and the specialized thecal pores and slits that most investigators believe faced away from the substrate. In contrast, the mitrates were adapted to an infaunal life mode. They have a streamlined, generally symmetrical body composed of relatively large thecal plates that lack knobs and protuberances. In many species, transverse cuesta-like ribs on the theca, marginal denticles, and forward imbrication of thecal plates would serve to grip the substrate and inhibit removal by either predators or currents.
