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Morphology evidences the lophophorates monophyly: brief review of studies on the lophophore innervation
The status of the Lophophorates is one of the central problems of current zoology. There is a contradiction between the molecular results, which mainly indicate the polyphyly of the lophophorates, and morphological results, which indicate the monophyly of the lophophorates. An understanding of lophophore innervation can help answer question about the status of the lophophorates. Data on the lophophore innervation, which were obtained by methods of immunocytochemistry, transmission electron microscopy, and laser confocal scanning microscopy in species from all three groups of the lophophorates, are summarized in this report. According to morphological results, the lophophore has several main nerves that seem to be homologous among different lophophorates. The main brachial nerve of brachiopods is homologous to the dorsal ganglion of phoronids and to the cerebral ganglion of ectoprocts. The accessory brachial nerve of brachiopods is homologous to the minor nerve ring of juvenile phoronids and to the circum oral nerve of ectoprocts. The lower brachial nerve of brachiopods is homologous to the tentacular nerve ring of phoronids and to the outer nerve of ctenostome ectoprocts. Morphological data on the lophophore innervation indicate that the Lophophorata is monophyletic group including three phyla: Phoronida, Brachiopoda, and Bryozoa. Contradiction between morphological and molecular results might be explained by of bryozoans, whose evolution was associated with great morphological and, apparently, molecular changes. To reject the lophophorates monophyly we should suggest the independent origin of the lophophore — a specific tentacular structure having specific innervation — in both Bryozoa and Brachiozoa (= Phoronida + Brachiopoda).