Temereva E.N., Kosevich I.A. 2018. Organization of the lophophoral nervous system in the cyclostome bryozoans confirms the relationship of the Bryozoa and Brachiozoa // Invertebrate Zoology. Vol.15. No.4: 366–372 [in English].
Dept. Invertebrate Zoology, Biological Faculty, Moscow State University, Moscow, 119991 Russia. E-mail: email@example.com
ABSTRACT: The phylogeny of bryozoans is ambiguous and apparently cannot be resolved by molecular methods alone. Morphological data from previously unstudied species may help establishing relationships between the main groups of the Bryozoa and may help to clarify bryozoan phylogeny. The Cyclostomata is the least studied group of bryozoans. The nervous system of cyclostomes has not been described utilising modern methods until this year. The recent data, which were obtained from two different cyclostome species, revealed some lophophoral nerves may be compared with the lophophore nervous elements in other lophophorates. In this paper, new data on organization of the nervous system in cyclostome Cinctipora elegans and Crisia eburnea are discussed in frame of the problem of the lophophorates monophyly. In both cyclostome species, the cerebral ganglion gives rise to circumoral nerve ring and outer nerve ring. The circumoral nerve ring gives rise to frontal neurite bundles of tentacles and intertentacular neurite bundles, which extend between tentacles at their base. Each tentacle is innervated by six (in Crisia eburnea) or four (in Cinctipora elegans) longitudinal neurite bundles. In addition to these intraepithelial neurite bundles, the peritoneal neurites pass along the lateral sides of each tentacle between peritoneal lining and extracellular matrix. The outer nerve ring extends along the outer surface of the lophophore at the base of tentacles. The outer nerve ring was previously described only in ctenostome Amathia gracilis. The outer nerve ring may be regarded homologous to the terntacular nerve ring in phoronids and lower brachial nerve in brachiopods. The similarities in the innervation of the lophophore and tentacles in all lophophorates are consistent with the view that the Bryozoa and Brachiozoa are closely related.
KEY WORDS: cerebral ganglion, tentacles, lophophore, lophophorates, evolution, phylogeny.