Victoriniella multiformis, gen. et spec. nov. (incerta sedis), a polymorphic parasitoid protist infecting the marine diatom Coscinodiscus wailesiiGran & Angst (North Sea, German Bight)

Victoriniella multiformis gen. et sp. nov. is a polymorphic parasitoid of uncertain taxonomic position that infects the marine centric diatom Coscinodiscus wailesii. Motile trophozoites attached to the diatom protoplast by means of a pseudopodium which was also used for incorporation of host cytoplasm. At the end of the trophic phase several filose pseudopodia were frequently formed which were used for locomotion. Thereafter, two divisions frequently followed, and led to the formation of cone-shaped cells of characteristic shape which left the empty frustule. Among the offspring two forms of motile stages were observed: Cells of type A were free-swimming and possessed two anterior inserted flagella, whereas cells of type B did not swim but moved by means of two contractile filopodia. Occasionally, cyst formation was observed inside infected diatoms.