The photo below is of a rhizomycelial marine chytrid, genus Nowakowskiella or Cladochytrium; the sporangium below is about 25 microns across -- after dissolution of the plug at the tip, swimming zoospores (posteriorly uniflagellate, 3 to 5 microns diam) are released. It is a very regular occupant of living green leaf blades of turtlegrass (Thalassia testudinum). It is not easily cultured, and may not be viable without the living host. [UPDATE: Sharon Mozley has it in culture! -- emozley@dogwood.botany.uga.edu] Could it be involved in turtlegrass dieback, under conditions of stress to the seagrass?! See Newell SY and JW Fell. 1980. Mycoflora of turtlegrass (Thalassia testudinum Konig) as recorded after seawater incubation. Bot. Mar. 23:265-275.