Ectocarpus has a life history with an isomorphic alternation of generation. The diploid filament (right) forms sporangia without internal walls and within which meiosis occurs. Thus, they are called unilocular meiosporangia (or unilocular zoosporangia). The haploid filament (left) forms gametangia with many internal walls (pleurilocular gametangia, or more correctly, pleurilocular isogametangia). Diploid filaments may also form pleurilocular structures in which 2n zoospores are produced. The motile cells in the center show a gamete or zoospore (top left); fusing gametes (bottom left); and a zygote (right).

from: http://biodidac.bio.uottawa.ca/Thumbnails/showimage.cfm?File_name=Phae009b&File_type=gif