Oedogonium has an unusual sexual life history the is haplontic and oogamous.  Cells in the female filaments differentiate to form oogonia the bear a single egg.  The male filaments (in certain species) release androspores (ASP), specialized zoospores that seek out the oogonium and attach.  There, they germinate to produce a dwarf male filament which produces two sperm.  These fertilize the egg, making a zygote.  The zygote germinates by producing 2-4 zoospores which develop into the respective male and female filaments.  The filaments may reproduce asexually by producing zoospores or vegetatively by fragmentation.