ИСТИНА

It is known that echinoderms have very peculiar body plan, the fact is that their radial and bilateral structures are mixing. The most characteristic feature of it is axial complex, which have captured our attention for several years. Now we have restudied and compared axial complexes of Asterias rubens Linnaeus, 1758 (Asteroidea) and Strongylocentrotus pallidus Sars, 1872 (Echinoidea) with the 3D software to illustrate their shape, proportion and interrelation. Three specimens of A. rubens were collected near the Pertsov White Sea Biological Station in 2008, two specimens of S. pallidus – near the Seasonal Biological Station Dalnie Zelentsy in 2014. The material was cut into serial sections by the standard histological technique. Two series of sections were used for 3D modelling. The axial complexes of A. rubens and S. pallidus consist of the coelomic organs (water-vascular system, axial coelom, pericardial coelom, perihaemal canals and gonad), and haemocoelic organs (axial organ, oral haemal ring, and haemal lacunae of gut and gonad). The water-vascular system communicates with the axial coelom. The pericardial coelom and the gonad coelom are closed. The haemocoelic organs are connected with each other and with entirely haemal system. All these structures have arranged in a very similar way with some minor differences. Unlike A. rubens, S. pallidus has well-developed perioral coelom and only one perihaemal ring. Organization of echinoderm axial complex is supposed to have considerable phylogenetic significance and needs further analysis.