A new intranuclear microsporidium, Enterospora nucleophila n. sp., causing an emaciative syndrome in a piscine host (Sparus aurata), prompts the redescription of the family Enterocytozoonidae

- A new species of microsporidium is described from the intestine of a marine teleost.
- The ultrastructural and molecular analyses place it within the Enterocytozoonidae.
- The Enterocytozoonidae family is amended.
- Intranuclear stages are free in the nucleoplasm and those in the cytoplasm are in a parasitophorous vacuole.
- This microsporidium is a potential threat for cultured fish as it drastically reduces growth.