Urosporoidea superfam. n. and Veloxidium. The third class was created – Squirmida – for Filipodium and Platyproteum. Thus, the eugregarines proved to be split and distributed among these three classes together with some other apicomplexans. This point of view was challenged in 2017 by Simdyanov and co-authors, who performed the global integrated analysis of available morphological and molecular phylogenetic data and concluded that eugregarines are rather a monophyletic taxon. Several genera of gregarines are currently not classified: Acuta, Cephalolobus, Gregarina, Levinea, Menospora, Nematocystis, Nematopsis, Steinina, and Trichorhynchus. Characteristics Meiosis occurs in all species. Monoxenous – only one host occurs in lifecycle for almost all species. Mitochondria have tubular cristae and are often distributed near the cell periphery. Apical complex occurs in the sporozoite stage, but is lost in the trophozoite stage in eugregarines and neogregarines. Trophozoites have a large and conspicuous nucleus and nucleolus. They inhabit extracellular body cavities of invertebrates such as the intestines, coeloms, and reproductive vesicles. Attachment to host occurs by a mucron (aseptate gregarines) or an epimerite (septate gregarines); some gregarines (urosporidians) float freely within extracellular body cavities (coelom). The parasites are relatively large, spindle-shaped cells, compared to other apicomplexans and eukaryotes in general (some species are in length). Most gregarines have longitudinal epicytic folds (bundles of microtubules beneath the cell surface with nematode like bending behaviour): crenulations are instead found in the urosporidians. Molecular biology The gregarines are able to move and change direction along a surface through gliding motility without the use of cilia, flagella, or lamellipodia. This is accomplished through the use of an actin and myosin complex. The complexes require an actin cytoskeleton to perform their gliding motions. In the proposed ‘capping’ model, an uncharacterized protein complex moves rearward, moving the parasites forward. History The gregarines are among the oldest known parasites, having been described by the physician Francesco Redi in 1684. The first formal description was made by Dufour in 1828. He created the genus Gregarina and described Gregarina ovata from Folficula aricularia. He considered them to be parasitic worms. Koelliker recognised them as protozoa in 1848. References Further reading External links Tree of Life Gregarina Gregarina Movies SAR supergroup subclasses Conoidasida Apicomplexa genera