Descriptions of two new families — Polysporoplasmidae fam. n. (Syn. Sphaerosporidae Davis, 1917 in Sitja-Bobadilla, Alvarez-Pellitero, 1995) and Gadimyxidae fam. n. (syn. Parvicapsulidae Schulman, 1953 in Kinie et al., 2007), and one new species of myxosporeans — Gadimyxa ovale sp. n. — parasites of fishes of the Mediterranean and the Black Seas are presented. Species of the genus Gadimyxa is found for the first time in the Black Sea.