Abstract
Ultrastructure of the marine lignicolous, bitunicate, ascomycete Massarina thalassiae is presented and compared with marine species of the genera Paraliomyces, Pleospora and Nimbospora. Asci of M. thalassiae possess a thick endoascus, thin ectoascus and an ocular chamber. The bicelled ascospores are surrounded by an exosporial mucilaginous sheath similar to that of Paraliomyces lentiferus.