Mesochytrium penetrans gen. et sp nov (Chytridiales) - a parasite of the green alga Chlorococcum minutum (Chlorococcales), with an unusual behaviour of the sporangia

Mesochytrium penetrans gen. et sp. nov. is an obligate parasite of the gree n alga Chlorococcum minutum. Spherical zoospores with a posterior flagellum contain a rumposome, microtubule roots, and a single lipid globule. Riboso mes are concentrated around the nucleus and form an ill-defined ribosome ag gregate. The pyriform zoosporangium partly penetrates the host cell; zoospo res escape through a single wide apical opening. The empty sporangium has a goblet-like shape, it lies partly inside the algal cell wall. Delicately b ranched rhizoids arise from a sole main axis on the base of the sporangium. Resting spherical spores are endobiotic; their wall is thick and smooth.