A New Marine Species of () Parasitic to sp. in Iceland.

Obligate endoparasitic oomycetes are known to ubiquitously occur in marine and freshwater diatoms, but their diversity is still largely unexplored. Many of these parasitoids are members of the early-diverging oomycete lineages (, ), others are within the of the (, ) and some have been described in the (, ). Even though some species have been recently described and two new genera were introduced ( and ), the phylogeny and taxonomy of most of these organisms remain unresolved. This is contrasted by the high number of sequences from unclassified species, as recently revealed from environmental sequencing, suggesting the presence of several undiscovered species. In this study, a new species of is reported from a marine centric diatom ( sp.) isolated from Skagaströnd harbor in Northwest Iceland. The morphology and life cycle traits of this novel oomycete parasite are described herein, and its taxonomic placement within the genus is confirmed by molecular phylogeny. As it cannot be assigned to any previously described species, it is introduced as in this study. The genus thus contains three described holocarpic species (, , ) to which likely additional species will need to be added in the future, considering the presence of several lineages known only from environmental sequencing that clustered within the clade.