Many marine colonial invertebrates host bacterial symbionts. They were also described in several bryozoan species, but details of their interaction with host tissues studied very fragmentarily. Ultrastructural research on two closely related cheilostome bryozoans – Aquiloniella scabra and Paralicornia sinuosa have revealed the presence of symbiotic bacteria inside so-called ‘funicular bodies’, that are swollen parts of funicular strands providing transport function within and between zooids. Funicular bodies are morphologically similar in both species. The size of the bodies correlates with the number of symbionts inside of them. Presence of the electron dense matrix in the gaps between symbionts and cytoplasmic processes of the host cells, as well as an increase of the funicular bodies in size, may indicate trophic relationships between the bryozoan tissues and bacteria. Thus, funicular bodies can serve as a reservoir for the maintenance of the vital activity of bacteria and their multiplication. Viral particles were detected in the cytoplasm of bacterial symbionts of P. sinuosa. Presence of viruses in bryozoans has not yet been detected. Amount of bacteriophages differs in the bacteria from different funicular bodies. We found intact bacterial cells, cells with virions in the cytoplasm and disrupted bacteria containing virions. Differences can be associated with the asynchronous occurrence of the lytic cycle in bacteria from different funicular bodies. Interestingly, viral particles possess a larger and more complex capsid then those of most bacteriophages known.