Ascospore and spore appendage ultrastructure inPleospora gaudefroyiis described. Ascospore walls comprise a three-layered mesosporium within which electron-dense bodies (melanin?) are deposited in two layers (W2, W3), a tripartite episporium (W4), and an outer mucilaginous sheath (exosporium?). The electron-dense inclusions in the mesosporium are compared with those in the conidia ofAlternaria brassicicolaand ascospores ofCarbosphaerella leptosphaerioides. In the unitunicate marine Ascomycetes, ascospores with a sheath are uncommon, whereas in the Loculoascomycetes many species have such ascospores. The sheath inP.gaudefroyiis compared with those ofParaliomyces lentiferus,Massarina thalassiae, andMassarina armatispora(all Loculoascomycetes).Key words: appendage ontogeny, marine Ascomycotina, taxonomy, ultrastructure.