Myxozoa (etymology: Greek: μύξα myxa "slime" or "mucus" + thematic vowel o + ζῷον zoon "animals") is a group of aquatic, obligately parasitic cnidarian animals. Over 1300 species have been described and many have a two-host lifecycle, involving a fish and an annelid worm or a bryozoan. The average size of a myxosporean spore usually ranges from 10 μm to 20 μm, whereas that of a malacosporean spore can be up to 2 mm. Myxozoans can live in both freshwater and marine habitats.