Ovicell development in the early calloporid Wilbertopora Cheetham, 1954 (Bryozoa: Cheilostomata) from the mid-Cretaceous of the USA

The calloporid Wilbertopora Cheetham, 1954 is the oldest known cheilostome with brood chambers (ovicells). The pattern of initial ovicell formation, involving a single ooecial rudiment, is more reminiscent of ovicell development in some Recent cribrimorphs and other more advanced cheilostomes than it is of Recent calloporids that have a double rudiment. The distrubution of early ovicell developmental types among cheilostomes is discussed. During later ovicell growth in Wilbertopora two lateral lobes fuse to form the hemispherical hyperstomial ovicell. This fusion process demonstrates how such ovicells could have originated from a more primitive bispinose precursor.