Spore variability of Ceratomyxa appendiculata Thélohan, 1892, found in the gallbladder of black angler-fish, Lophius budegassa from NE Spain were studied by light microscopy and, for the first time, by scanning electron microscopy. More than 18,000 spores of C. appendiculata were examined, classified and quantified. Of this, 98.31% were bivalvular normal spores, the rest were abnormal spores (1.63% were trivalvular spores and 0.06% were tetravalvular spores). The monthly evolution of these spores was followed for ten months. Differences among the proportions of trivalvular spores in different months were significant. Percentage of trivalvular spores ranged from 9.90% (May) to 0.00% (December). The highest percentage of tetravalvular spores was reached in november (0.39%). Some polysporous trophozoites can produce simultaneously normal and abnormal spores.