selenidium selenidium selenidium is a genus of parasitic alveolates in the phylum apicomplexa. species in this genus infect marine invertebrates. selenidium scientific classification domain: eukaryota (unranked): sar (unranked): alveolata phylum: apicomplexa class: conoidasida subclass: gregarinasina order: eugregarinorida suborder: aseptatorina family: lecudinidae genus: selenidiumgiard, 1884 species selenidium alleni selenidium amphinomi selenidium annulatum selenidium axiferens selenidium branchiommatis selenidium brasili selenidium cantoui selenidium caulleryi selenidium cirratuli selenidium cometomorpha selenidium costatum selenidium cruzi selenidium curvicollum selenidium echinatum selenidium fallax selenidium fauchaldi selenidium flabelligerae selenidium filiformis selenidium foliatum selenidium folium selenidium francianum selenidium giganteum selenidium grassei selenidium halteroide selenidium hermellae selenidium hollandei selenidium intraepitheliale selenidium mackinnonae selenidium martinensis selenidium melinnae selenidium melongena selenidium mercierellae selenidium mesnili selenidium metchnikovi selenidium orientale selenidium parvum selenidium pendula selenidium pennatum selenidium pisinnus selenidium plicatum selenidium polydorae selenidium potamillae selenidium productum selenidium rayi selenidium sabellae selenidium sabellariae selenidium serpulae selenidium sipunculi selenidium spatulatum selenidium spinosis selenidium spionis selenidium stellatum selenidium synaptae selenidium telepsavi selenidium terebellae selenidium virgula taxonomy this genus was created by giard in 1884. fifty six species have been described in this genus. the type species is selenidium pendula giard, 1884. description all species in this genus infect marine invertebrates. life cycle these species infect the gut of polychaete worms. the trophozoites are vermiform with an apical complex. they have few epicytic folds. a dense array of microtubules lies under a trilayered pellicle. syzygy occurs in the tail-to-tail, head-to-head and lateral positions. the gamonts are extracellular. they are foliaceous or cylindroid in shape and have longitudinal striations. the oocysts are spherical or ovoid, are 12-18 microns in diameter and their wall is 1 micron thick. they have four infective sporozoites each. the sporozoites undergo schizogony (merogony).