ИСТИНА

The mechanism of radula renewal was studied in detail for several species of gastropods from different subclasses. However, there is no published data on these processes for opisthobranchs. In this research we studied general and fine morphology of the radular sheath of nudibranch species Flabellina verrucosa (M. Sars, 1829) and suggest the mechanism of its radula renewal. F. verrucosa is a common species of nudibranchs in the White Sea, which inhabits the subtidal zone. Forty-one specimens of F. verrucosa were collected near the White Sea Biological Station during summer seasons of 2012─2015. The observation of the general morphology of the radular sheath was performed using light microscopy and cLSM methods. As well, the 3D-reconstruction of the radular sheath distal end was constructed. To observe the fine structure of radular sheath distal end TEM was used.