Article: Systematics of Upper Cretaceous calloporid bryozoans with primitive spinose ovicells
Andrew N. Ostrovsky and Paul D. Taylor
The majority of fossil and Recent cheilostome bryozoans brood their larvae in ovicells. These double-walled, hood-like skeletal structures are thought to have arisen through modification of spines belonging to the zooid distal of the maternal zooid. Support for this hypothesis comes from the existence of ovicells constructed of multiple spines in a few Upper Cretaceous species belonging to two groups, microporids and cribrimorphs. Here we report the discovery of similar multispinose ovicells in a third group, calloporids, which are closely related to primitive cheilostomes that do not brood their larvae. The genus Distelopora Lang, 1915 from the Cenomanian ('Chalk Marl') of Cambridge is taken out of synonymy and shown to comprise the type species (D. bipilata) and two new species (D. langi and D. spinifera) of multiserial calloporids. Between 5 and 15 spine bases are arranged in a crescent on the gymnocyst of the zooid distal of each maternal (egg-producing) zooid in Distelopora. This indicates the presence of an ovicell formed by a cage of basally articulated spines. Similar ovicells represented by 18-19 spine bases occur in a uniserial calloporid from the German Campanian Allantopora krauseae Voigt and Schneemilch, 1986, which is made the type species of the new genus Unidistelopora. Another calloporid from the Cambridge Cenomanian has ovicells constructed by two claw-like, flattened, non-articulated and laterally juxtaposed spines. Described as Gilbertopora larwoodi gen. et sp. nov., this multiserial species provides a link between Distelopora and more typical cheilostome ovicells. The spines forming primitive ovicells provide a good example of exaptations, co-opted from their original function protecting the polypide of the distal zooid.