Peculiarities of Tentacle Innervation of Flustrellidra hispida and Evolution of Lophophore in Bryozoa

The study of the lophophore organization is of great importance for the reconstruction of lophophorate phylogeny and for understanding the evolutionary transformation in each phylum of Lophophorata. The innervation of the lophophore in ctenostome bryozoan Flustrellidra hispida was studied using immunocytochemistry and confocal laser scanning microscopy. It has been demonstrated that this species has an outer nerve ring giving rise to the tentacle nerves. The outer nerve ring was earlier described in some ctenostomates and cyclostomates, but not as connected with nerves. The discovered feature of lophophore innervation in F. hispida suggests the evolutionary transformation from a hypothetical phoronida-like ancestor lophophore bearing a prominent outer nerve ring with numerous tentacle nerves emanating from it, to the complex bell-shaped lophophore of F. hispida with a well-pronounced outer nervous ring bearing a few tentacle nerves. The next one in this hypothetical row is the lophophore of the other ctenostomates and some cyclostomates with no ring-nerve connection and cheilostomates lophophore with no outer nerve ring at all.