Orthonectida iku filum kecil parasit ora digelet pengertiané sekang invertebrata sagara sing salah siji organisme multiselular sing paling biyasa.

Biologi 

Gedene iku kéwan kaya cacing mikroskopis, sing lewih sekang siji lapisan sel njaba ana siliané sekitaré massa sel kelaminé. Kae rénang karo bébas ing tubuh inangé, sing kelebu platyhelminthes, cacing polychaeta, moluska bivalvia, lan echinodermata. Kae gonochoristic, karo individu lanang lan wadon misah.

Angger wis siyap kanggo réproduksi, kae lunga sekang inangé, lan sperma sekang lanang nembus awak sing wadon kanggo fertilisasi internal. Zigot sing dikasilna dadi larva ngabi silia sing lolos sekang biyungé kanggo nggolet inang anyar. Bar nemu inang, larva kelangan silia lan dadi larva plasmodium syncytial. Larva iki, gilirané, mecah dadi akèh sel-sel individual sing arep dadi génerasi selanjute.

Klasifikasiné 

Filum iki ana sekang 20 spésies sing dikenal, ing Rhopalura ophiocomae iku sing paling dikenal. Filum iki ora dibagi mengjero kelas utawa ordho, lan kur isi loro famili.

Awale dideskripsina déning taun 1877 kanggo kelas, lan kadang-kadang ditandai kanggo ordho ing filum Mesozoa, panalitèn anyar, orthonectids béda pisan karo rhombozoa, kelompok lain di Mesozoa.

Spesies sing wis katon:

Filum Orthonectida
 Famili Rhopaluridae Stunkard, 1937
 Ciliocincta akkeshiensis Tajika, 1979 – Hokkaido, Japan; in flatworms (Turbellaria)
 Ciliocincta julini (Caullery and Mesnil, 1899) – E North Atlantic, in polychaetes
 Ciliocincta sabellariae Kozloff, 1965 – San Juan Islands, WA (USA); in polychaete (Neosabellaria cementarium)
 Intoshia leptoplanae Giard, 1877 – E North Atlantic, in flatworms (Leptoplana)
 Intoshia linei Giard, 1877 – E North Atlantic, in nemertines (Lineus) = Rhopalura linei
 Intoshia major Shtein, 1953 – Arctic Ocean; in gastropods (Lepeta, Natica, Solariella) = Rhopalura major
 Intoshia metchnikovi (Caullery & Mesnil, 1899) – E North Atlantic, in polychaetes and nemertines
 Intoshia paraphanostomae (Westblad, 1942) – E North Atlantic, in flatworms (Acoela)
 Intoshia variabili (Alexandrov & Sljusarev, 1992) – Arctic Ocean, in flatworms (Macrorhynchus)
 Rhopalura elongata Shtein, 1953 – Arctic Ocean, in bivalves (Astarte)
 Rhopalura gigas (Giard, 1877)
 Rhopalura granosa Atkins, 1933 – E North Atlantic, in bivalves (Pododesmus)
 Rhopalura intoshi Metchnikoff – Mediterranean, in nemertines
 Rhopalura litoralis Shtein, 1953 – Arctic Ocean, in gastropods (Lepeta, Natica, Solariella)
 Rhopalura major Shtein, 1953
 Rhopalura murmanica Shtein, 1953 – Arctic Ocean, in gastropods (Rissoa, Columbella)
 Rhopalura ophiocomae Giard, 1877 – E North Atlantic, in ophiuroids (usually Amphipholis)
 Rhopalura pelseneeri Caullery & Mesnil, 1901 – E North Atlantic, polychaetes and nemertines
 Rhopalura philinae Lang, 1954 – E North Atlantic, in gastropods
 Rhopalura pterocirri de Saint-Joseph, 1896 – E North Atlantic, in polychaetes
 Rhopalura vermiculicola
 Stoecharthrum burresoni Kozloff, 1993
 Stoecharthrum fosterae Kozloff, 1993
 Stoecharthrum giardi Caullery & Mesnil, 1899 – E North Atlantic, in polychaetes
 Stoecharthrum monnati Kozloff, 1993 – E North Atlantic, in molluscs
 Famili Pelmatosphaeridae Stunkard, 1937
 Pelmatosphaera polycirri Caullery and Mesnil, 1904 – E North Atlantic, in polychaetes and nemertines

Préferensi 

Protostomia
Kéwan