<p>Cryptic diversity is a significant problem that prevents us from understanding of the biogeography and evolutionary history of taxa. In hydrozoans, the so-called cryptic diversity is often linked with gaps in life cycle knowledge due to low availability of hydroids, seasonality of reproduction, etc. Molecular phylogenetic analyses of specimens from the White Sea have revealed pseudocryptic species amongst hydroids of the family Bougainvilliidae, characterized by similar creeping colonies. As a result of field sampling and experimental study, I have gained insights into their life cycles and described two new species (<i>Bougainvillia jyrama</i> sp. nov. and <i>Bougainvillia marfenini</i> sp. nov.). I highlight low number of species of Bougainvilliidae in plankton of the White Sea. This pattern corresponds to the regional tendency of low number of meroplankton species in proportion to benthic hydrozoans with fixed gonophores. The reversible loss of medusae, referred to as “delayed medusa”, observed in hydrozoan populations <i>B. marfenini</i> sp. nov. and <i>Bouganivillia principis</i> within the White Sea, probably depends on environmental cues and requires further study. In addition, a multi-gene analysis of the phylogenetic relationships amongst bougainvilliids and the related taxa has been carried out, and phylogeny of the family Bougainvilliidae in the light of the new findings is presented.</p>