ИСТИНА

Monstrilloid copepods are widely distributed in the World’s Oceans and occur at different latitudes, reaching the highest diversity in the tropical zone. Monstrilloida have been fairly well-studied in the Northern Atlantic, including European waters, but are mostly unknown from the Southern Hemisphere, including the Antarctic Convergence. Only one species, Monstrillopsis ferrarii Suárez-Morales & Ivanenko, 2004, has been described from the White Sea based on adult females while the other stages of the life cycle are still unknown. In April 2021, male monstrilloids were found in plankton samples taken in the vicinity of the White Sea Biological Station, Moscow State University. Conspecificity of these males with the previously described females of M. ferrarii was confirmed using molecular genetic analysis based on LSU rDNA (28S) sequence data. Light, confocal, and scanning electron microscopy were employed to study the external morphology of the males and infective nauplius stage for the first time. In September 2016 a parasitic copepodid stage of a monstrilloid was found freely in a benthic sample in the White Sea, raising the question that it belonged to M. ferrarii. However, molecular analysis refuted conspecificity, providing evidence for the occurrence of a second, as yet undescribed, monstrilloid species in the White Sea. The external structure of the parasitic stage was examined using macro-photography.