Quantitative differences in mitochondrial ultrastructure of a thiobiotic and an oxybiotic turbellarian

Specimens of the thiobiotic acoel Solenofilomorpha funilis Crezée, 1975 and the oxybiotic acoel Otocelis sp. were collected from Mount Desert Island, Maine, USA in spring and summer of 1982, and the ultrastructure and distribution of their mitochondria were compared. The volume density and the surface density of the mitochondria are significantly higher in the epidermis and parenchyma of S. funilis than in the corresponding tissues of Otocelis sp. Surface densities of mitochondrial cristae are higher in all tissues studied (epidermis, muscle, and parenchyma) of S. funilis than in Otocelis sp. The differences in mitochondrial ultrastructure of these two species suggest that mitochondria in anaerobic tissues differ in function from their aerobic counterparts.