ИСТИНА

The Brachiopoda is a phylum of marine sedentary bivalve invertebrates with controversial phylogenetic position: they belong to protostomes but their morphology and development have a lot in common with deuterostomes. Coelom organization of brachiopods is supposed to be one of the most important morphological features for understanding brachiopods’ relationships, and their position within other bilaterians. Our work is an attempt to summarize all classical and modern data dedicated to anatomy, ultrastructure and, partially, development of coelomic system in Brachiopoda. We have discussed compartmentalization of the coelom in brachiopods and other lophophorates (bipartite or tripartite); coelom development and ultrastructure of coelomic lining in brachiopods and other bilaterians; the nature of uniqie lateral mesenteries in brachiopods and other lophophorates; origin of unusual brachiopod body plan. Enterocoely and presence of three coelomic compartments contribute to relationship between brachiopods and deuterostomes. On the other hand, brachiopods have some prominent protostome-like features such as the presence of annelid-like setae, specific expression of Hox genes, and protostomian fate of the blastopore in many species. A new information about coelom compartmentalization in Lingula anatina Lamarck, 1801 has shown that brachiopods likely retain both archimery resembling coelom organization in echinodermates, and metamery common for both protostome and deuterostome animals. This work accepts possibility to integrate archicoelomate and metameric hypotheses of bilaterian origin. Thus, coelomic organization study is truly one of the most perspective ways to reconstruct and understand brachiopod relations as well as origin and diversification of bilaterians. This work is supported by RFBR (#17-04-00586).