The diploporite blastozoan Glyptosphaerites (Echinodermata: Blastozoa) and the origin of diplopores

Glyptosphaerites is a stemless, directly attached diploporite characterized by five ambulacra that have multiple facets and extend over the theca, but entirely lack flooring and cover plates. The food grooves lack any systematic relationship to the underlying thecal plates and grew out from a mouth with a frame of six plates; five radial circumorals and a sixth interradial plate in the CD interambulacrum. The mouth was covered by a palate of eleven palatal plates. These characters are shared by most Sphaeronitidae, whereas traditionally Glyptosphaerites has been associated with diploporites that possess a stem and ambulacra with biserial flooring plates that alternate, left and right, and each of which supports a single brachiole facet. Such diploporites are characterized by Protocrinites, which has cover plates over its ambulacra and mouth but lacks a palate. Glyptosphaerites and Protocrinites are typical of two major divisions within the Diploporita, here called the Anambulacralia and Ambulacralia, respectively. The oldest identified anambulacralian is the middle Cambrian âeocrinoidâ Lichenoides. Diplopores of Glyptosphaerites leuchtenbergi arose on plate sutures as a single perpendicular canal like an epispire. This became incorporated into one plate as a second perpendicular canal developed on the suture. Further plate growth increased the separation of the two perpendicular canals until a standard distance was established when both canals became incorporated into the plate. Thus, the axes connecting perpendicular canals are perpendicular to plate sutures. In G. leuchtenbergi, diplopores were preferentially incorporated into one plate, often resulting in diplopores being concentrated in the adoral halves of thecal plates