Orthonectida
Orthonectida
Meadle
<catset>Category="Animals"</catset><table border=1 cellpadding=0 style="position:relative; margin: 0 0 0.5em 1em; border-collapse: collapse; float:right; clear:right; width:200px;"><tr style="text-align:center;"><th style=" background: pink;"><div style="float:right; font-size:70%; padding:0 .5em 0 2em">?</div><b> Orthonectids</b></th></tr><tr style="text-align:center;"><th style=" background: pink;"><b><a href="Scientific classification">Scientific classification</a></b></th></tr><tr style="text-align:center;"><td> <table cellpadding=2 style="margin:0 auto; text-align:left; background:none;"><tr valign=top><td>Kingdom:</td><td><a href="Animal">Animalia</a></td></tr><tr valign=top><td>Phylum:</td><td><b>Orthonectida</b><br><small> Giard,&nbsp; 1880</small></td></tr></table></td></tr></table><p><b>Orthonectida</b> is a small <a href="Phylum">phylum</a> of poorly-known <a href="Parasite">parasites</a> of marine invertebrates that are among the simplest of multi-cellular organisms. Members of this phylum are known as <b>orthonectids</b>.<p>Multinucleate plasmodia give rise to sexual males and females, which are free-swimming by means of <a href="Cilium">cilia</a>. They are composed of a single layer of ciliated outer cells surrounding a mass of sex cells. 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.<p>Parasitized organisms include <a href="Flatworm">flatworms</a>, <a href="Polychaete">Polychaete</a> worms, <a href="Bivalvia">bivalve</a> molluscs, and <a href="Echinoderm">echinoderms</a>.<p>The phylum consists of about 20 known species, of which <i>Rhopalura ophiocomae</i> is the best-known.<p>Originally described in <a href="1880">1880</a> as a class, and sometimes characterized as an order of <a href="Mesozoa">Mesozoa</a>, recent study shows that orthonectids are indeed quite different from <a href="Rhombozoa">rhombozoans</a>, the other group in Mesozoa.<p>Known species:<ul><li> Family Rhopaluridae <ul> <li> <i>Ciliocincta julini</i> (Caullery and Mesnil, 1899) - E North Atlantic, in polychaetes <li> <i>Intoshia leptoplanae</i> (Giard, 1877) - E North Atlantic, in flatworms (<i>Leptoplana</i>) <li> <i>Intoshia linei</i> (Giard, 1877) - E North Atlantic, in nemertines (<i><a href="Lineus longissimus">Lineus</a></i>) = <i>Rhopalura linei</i> <li> <i>Intoshia major</i> (Shtein, 1953) - Arctic Ocean; in gastropods (<i>Lepeta</i>, <i>Natica</i>, <i>Solariella</i>) = <i>Rhopalura major</i> <li> <i>Intoshia paraphanostomae</i> (Westblad, 1942) - E North Atlantic, in flatworms (<i>Acoela</i>) <li> <i>Rhopalura elongata</i> (Shtein, 1953) - Arctic Ocean, in bivalves (<i><a href="Astarte">Astarte</a></i>) <li> <i>Rhopalura gigas</i> (Giard, 1877) <li> <i>Rhopalura granosa</i> (Atkins, 1933) - E North Atlantic, in bivalves (<i>Pododesmus</i>) <li> <i>Rhopalura intoshi</i> (Metchnikoff) - Mediterranean, in nemertines <li> <i>Rhopalura litoralis</i> (Shtein, 1954) - Arctic Ocean, in gastropods (<i>Lepeta</i>, <i>Natica</i>, <i>Solariella</i>) <li> <i>Rhopalura metschnikowi</i> (Caullery and Mesnil, 1901) - E North Atlantic, in polychaetes and nemertines <li> <i>Rhopalura murmanica</i> (Shtein, 1953) - Arctic Ocean, in gastropods (<i>Rissoa</i>, <i>Columbella</i>) <li> <i>Rhopalura ophiocomae</i> (Giard, 1877) - E North Atlantic, in ophiuroids (usually <i>Amphipholis</i>) <li> <i>Rhopalura pelseeneri</i> (Caullery and Mesnil, 1901) - E North Atlantic, polychaetes and nemertines <li> <i>Rhopalura philinae</i> (Lang, 1951) - E North Atlantic, in gastropods <li> <i>Rhopalura pterocirri</i> (de Saint-Joseph, 1896) E North Atlantic, in polychaetes <li> <i>Rhopalura variabili</i> (Alexandrov and Sljusarev, 1992) - Arctic Ocean, in flatworms (<i>Macrorhynchus</i>) <li> <i>Stoecharthrum giardi</i> (Caullery and Mesnil, 1899) - E North Atlantic, in polychaetes <li> <i>Stoecharthrum monnati</i> (Kozloff, 1993) - E North Atlantic, in molluscs </ul> </ul><ul><li> Family Pelmatosphaeridae <ul> <li> <i>Pelmatosphaera polycirri</i> (Caullery and Mesnil, 1904) - E North Atlantic, in polychaetes and nemertines </ul> </ul><h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">References</h2><ul><li> Giard, E., "The Orthonectida, a new class of the phylum of the worms" <i>Quart. J. Microsc. Sci.</i>, 1880 n.s. 20: 225-240 <li> Hanelt B, Van Schyndel D, Adema CM, Lewis LA, Loker ES, "The phylogenetic position of Rhopalura ophiocomae (Orthonectida) based on 18S ribosomal DNA sequence analysis", <i>Mol Biol Evol.</i> 1996 Nov;13(9):1187-91 </ul>