Haematractidium is a genus of parasitic alveolates in the phylum Apicomplexa. It infects the Atlantic mackerel (Scomber scombrus). History This genus was first described by Henry in 1910. Although it is occasionally re described very little is known about it. Taxonomy There is one known species in this genus: Haematractidium scombri. Description The parasite is intra erythrocytic, ameboid, oval or pyriform in shape. There are no vacuoles or reticulation in the cytoplasm. The nucleus has two or more chromatin granules. The parasite has a single membrane. References Apicomplexa genera Parasites of fish