Description of two new coexisting parasitoids of blooming dinoflagellates in the Baltic sea: Parvilucifera catillosa sp. nov. and Parvilucifera sp. (Perkinsea, Alveolata).

• Infections of Parvilucifera species are reported for first time in the Inner Baltic Sea. • Parasitoids were isolated from a bloom that included toxic Alexandrium ostenfeldii. • Parvilucifera sp. and P. catillosa host range were restricted to dinoflagellates. • Parasitoids coexisted in the same habitat, but showed different host preferences. • The most distinctive feature of P. catillosa is the large and protuberant apertures. Perkinsea are a group of intracellular protist parasites that inhabit all types of aquatic environments and cause significant population declines of a wide variety of hosts. However, the diversity of this lineage is mostly represented by environmental rDNA sequences. Complete descriptions of Perkinsea that infect marine dinoflagellates have increased in recent literature due to the identification, isolation and culturing of representatives during bloom events, contributing to expand the knowledge on the diversity and ecology of the group. Shallow coastal areas in the Baltic Sea suffer seasonal dinoflagellate blooms. In summer 2016, two parasitoids were isolated during a Kryptoperidinium foliaceum bloom in the Baltic Sea. Morphological features and sequences of the small and large subunit of the ribosomal DNA gene revealed these two parasitoids were new species that belong to the genus Parvilucifera. This is the first time that Parvilucifera infections are reported in the Inner Baltic Sea. The first species, Parvilucifera sp. has some morphological and phylogenetic features in common with P. sinerae and P. corolla , although its ultrastructure could not be studied and the formal description could not be done. The second new species, named Parvilucifera catillosa , has several distinct morphological features in its zoospores (e.g. the presence of a rostrum), and in the shape and size of the apertures in the sporangium stage, which are larger and more protuberant than in the other species of the genus. Infections observed in the field and cross-infection experiments determined that the host range of both Parvilucifera species was restricted to dinoflagellates, each one showing a different host preference. The coexistence in the same environment by the two closely related parasitoids with very similar life cycles suggests that their niche separation is the preferred host. [ABSTRACT FROM AUTHOR]