Description of Haplosporidia
Circumscription: Sporozoan parasites of mostly marine invertebrates. Trophic cells uninueleate or multinucleate, intracellular, and no flagella. Spore walls develop intracellularly from haplosporosomes, and the spore has a distinctive lid and often extraneous filaments. Held by some to be related to the alveolates, but there is no evidence of alveoli. Ultrastructural identity: Mitochondria with tubular cristae. Dividing nucleus with internal spindle and the nuclear envelope remains intact. There is a residuum of parallel microtubules from the mitotic spindle, and this kernstab persists through interphase. Synapomorphy: Tubulocristate protists with lidded spore and/or persistent spindle (Kernstab) in nondividing nucleus. Composition: Several genera with about 35 nominal species.