This is the sputnik-like zoosporangium of Halophytophthora spinosa, a warm-water oomycote species limited to the tropics and subtropics. Variety spinosa is limited to the Atlantic Ocean, and variety lobata to the Pacific. H. spinosa is a weak competitor with Halophytophthora vesicula when there is a large source of zoospores nearby (e.g., large deposits of decaying leaves of red mangroves). When the zoospore source is weak, for some reason (better persistence in the water column?), H. spinosa is more frequent in decaying leaves of mangroves than is H. vesicula. When the zoospores of H. spinosa are mature, an exit tube will form through which the zoopospores can swim away. If the sporangium is stranded above the water line (on a micro scale), the exit tube will grow until it reaches water into which it can release its zoospores. See Newell SY, Fell JW, 1997, Competition among mangrove oomycotes, and between oomycotes and other microbes. Aquat Microb Ecol 12:21-28.