Detailed data on anatomy of the coelomic system and ultrastructure of the lophophore coelom in brachiopod Novocrania anomala with discussion of the phylogenetic significance

Zoologischer Anzeiger. 2026. Vol. 325. P. 182–195.

Temereva E.

Brachiopoda is a group of animals, that is still insufficiently studied at the ultrastructural level, despite the significance of ultrastructure of tissues and organs for analysing the functional morphology, reconstructing the organisation and biology of numerous extinct brachiopods, and establishing relationships among major taxa. In the present study, we provide a revised reconstruction of the coelomic system based on microtomography, and the first description of the ultrastructure of the lophophore coelomic lining in Novocrania anomala using transmission electron microscopy. N. anomala, and possibly other craniiform brachiopods, are characterised by a highly complex organisation of the coelomic system, which consists of six separate compartments, including two compartments in the lophophore and four in the trunk. Within the lophophore, the coelomic lining is organised into four main patterns: (1) simple myoepithelium, (2) myoepithelium transformed into large muscles, (3) alternating myoepithelial and peritoneal cells, and (4) peritoneum. The data obtained allowed us to reconstruct possible mechanism of lophophore protraction through relaxation of the lophophore muscles and straightening of the coelomic sinuses, assisted by brachial protractor muscles. We also provide considerations on the peristalsis of the anterior part of the alimentary tract. Our results are compared with the recent studies on the ultrastructure of the lophophore in rhynchonelliform and linguliform brachiopods, demonstrating that, at the ultrastructural level, Craniiformea appear to exhibit the most primitive cytological organisation of the lophophore coelomic system. A comparative analysis of data on the coelomic lining organisation revealed the presence of simple myoepithelium as a common type of lining in Craniiformea and Linguliformea, but not in Rhynchonelliformea. 

Keywords: эволюция, Brachiopoda, coelomic system, Lophophore, брахиоподы, целомическая система