Maullinia ectocarpii gen. et sp nov (Plasmodiophorea), an intracellular parasite in Ectocarpus siliculosus (Ectocarpales, Phaeophyceae) and other filamentous brown algae

An obligate intracellular parasite infecting Ectocarpus spp. and other fila mentous marine brown algae is described. The pathogen forms an unwalled mul tinucleate syncytium (plasmodium) within the host cell cytoplasm and causes hypertrophy. Cruciform nuclear divisions occur during early development. M ature plasmodia become transformed into single sporangia, filling the host cell completely, and then cleave into several hundred spores. The spores ar e motile with two unequal, whiplash-type flagella inserted subapically and also show amoeboid movement. Upon settlement, cysts with chitinous walls ar e formed. Infection of host cells is accomplished by means of an adhesorium and a stachel apparatus penetrating the host cell wall, and injection of t he cyst content into the host cell cytoplasm, The parasite is characterized by features specific for the plasmodiophorids and is described as a new ge nus and species, Maullinia ectocarpii.