Name: Orthonectids.
ZoologyAnimals; the simplest of multi-cellular organisms; poorly-known; parasites of marine invertebrates, like flatworms, polychaete worms, bivalve molluscs, and echinoderms; multinucleate plasmodia give rise to sexual males and females.
Motion: free-swimming by means of cilia, composed of a single layer of ciliated outer cells surrounding a mass of sex cells.
Reproduction: when a female is inseminated, the eggs develop into ciliated larvae that seek out new hosts and then break up into individual cells that become the next generation of plasmodia.
TaxonomyOriginally described in 1880 as a class, sometimes characterized as an order of
Mesozoa. Recent study shows that orthonectids are indeed quite different from rhombozoans, the other group in
Mesozoa.
Family RhopaluridaeCiliocincta 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 (Sabellaria 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 paraphanostomae (Westblad, 1942) - E North Atlantic, in flatworms (Acoela)
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, 1954) - Arctic Ocean, in gastropods (Lepeta, Natica, Solariella)
Rhopalura metschnikowi (Caullery and Mesnil, 1901) - E North Atlantic, in polychaetes and nemertines
Rhopalura murmanica (Shtein, 1953) - Arctic Ocean, in gastropods (Rissoa, Columbella)
Rhopalura ophiocomae (Giard, 1877) - E North Atlantic, in ophiuroids (usually Amphipholis)
Rhopalura pelseeneri (Caullery and Mesnil, 1901) - E North Atlantic, polychaetes and nemertines
Rhopalura philinae (Lang, 1951) - E North Atlantic, in gastropods
Rhopalura pterocirri (de Saint-Joseph, 1896) E North Atlantic, in polychaetes
Rhopalura variabili (Alexandrov and Sljusarev, 1992) - Arctic Ocean, in flatworms (Macrorhynchus)
Stoecharthrum giardi (Caullery and Mesnil, 1899) - E North Atlantic, in polychaetes
Stoecharthrum monnati (Kozloff, 1993) - E North Atlantic, in molluscs
Family Pelmatosphaeridae
Pelmatosphaera polycirri (Caullery and Mesnil, 1904) - E North Atlantic, in polychaetes and nemertines