The ultrastructure of Mychonastes ruminatus gen. et sp. nov., a new member of the Chlorophyceae isolated from brackish water

A new monotypic genus of the Chlorophyceae isolated from brackish water of the Chesapeake Bay, Maryland, U.S.A. is described as Mychonastes ruminatus. The alga is compared with similar members of the Oocystaceae. Based on the presence of a thick ruminate cell wall, the lack of discernible pyrenoids, and other vegetative characters, Mychonastes can be delineated from other green coccoid unicells.

The cellular life cycle of Mychonastes was studied by electron microscopy and compared to published studies of Chlorella. The genera are differentiated by wall and chloroplast structure. Mychonastes cell wall is sculptured and changes during the life cycle from a highly irregular appearance when young, to a less irregular state when mature. Mychonastes chloroplast lacks pyrenoids at all times. Chlorella has a smooth wall and pyrenoids which are apparent just after release from the mother cell until division. Organelles of both genera migrate in a similar pattern throughout the life cycle, with Mychonastes producing two or four autospores, and Chlorella producing four or more (rarely two).