Henneguya cartilaginis n. sp. (Myxozoa: Myxosporea) in the head cartilage of masu salmon Oncorhynchus masou masou

► Henneguya cartilaginis n. sp. was found from masu salmon Oncorhynchus masou masou. ► Infected fish exhibited cranial protrusion due to the myxosporean cysts in the head. ► Histological observation revealed that plasmodia developed in the head cartilage. ► Molecular analysis showed that H. cartilaginis was distinct from known species.