The ultrastructure of Capronia ciliomaris, an intertidal marine fungus from San Juan Island

A collection of Capronia ciliomaris (Herpotrichiellaceae, Dothideales, Asco mycota) from San Juan Island, Washington State, USA, was studied. Ul-trastr uctural examination elucidated the nature of structures observed previously at the light microscope level and revealed others not recorded in the orig inal description. Interthecial filaments are lacking while periphysoids (se nsu Muller et al 1987) arise from the upper third of the ascomal wall, exte nding through the ostiolar canal and merging with the apical setae. The asc us is bitunicate, lacks an ocular chamber, the endoascus forming a thickeni ng at the ascus apex. The ascospore wall comprises two layers: a bilamellat e mesosporium (the outer layer is more electron dense) and an electron-dens e episporium. Ascospores are verrucose, with projections arising from the o uter mesosporium and surrounded by the episporium. Ascospore appendages are subterminal and arise from the mesosporium through discontinuities in the episporium and extend to the septum. Spores and appendages are surrounded b y a delimiting membrane. The taxonomic position of Capronia is discussed.