Article: Ovicells in the Palaeozoic bryozoan order Fenestrata
The occurrence and morphology of fenestrate ovicells is reviewed and ovicells are described for the first time in Penniretepora. Four ovicell types are recognized and the considerable variation in morphology, size, position, and intra-colonial abundance of ovicells at generic level is related to variation in the morphology of autozooecial chambers, proximity of autozooecia, and the number of autozooecial rows on branches and dissepiments. Type A ovicells from large globose distentions to gonozooecia, are intra-colonially few in number and occur in Fenestella, Hemitrypa, and Penniretepora; Type B ovicells occur in Septatopora, and form shallow hemispherical depressions at the proximal rims of autozooecial apertures and are connected to the lower vestibular regions of adjacent gonozooecia by an auxiliary tube; Type C ovicells occur in Synocladia, Acanthodadia, and Thamniscus, and form hemispherical depressions at the proximal rims of autozooecial apertures and are intra-colonially very abundant; Type D ovicells are extrazooidal and occur in Polypora, ovicells are located on dissepiments and are linked to gonozooecia by a system of canal-like structures traversing branches and dissepiments, several gonozooecia shared an ovicell. Ovicell morphology may be of phylogenetic significance and of value at higher taxonomic rank in fenestrates.