| ONCF | ONCFM | Onch'ŏn-gun |
| Onch'on-gun | Onchan | Onchan (ort) |
| Onchan, Isle of Man | Onch’ŏn | Onch’ŏn-gun |
| Oncheon-dong | Oncheon-dong (socken i Sydkorea, Daejeon) | Oncheon-dong (socken i Sydkorea, Pusan, Dongnae-gu, lat 35,22, long 129,07) |
| Oncheon-dong, Busan | Oncheon-dong, Daejeon | Onchestus |
| Onchestus gorgus | Onchestus pasimachus | Onchestus rentzi |
| Onchidella | Onchidella patelloides | Onchidiidae |
| Onchidina | Onchidina australis | Onchidiopsis |
| Onchidiopsis corys | Onchidiopsis glacialis | Onchidiopsis groenlandica |
| Onchidiopsis hannai | Onchidiopsis kingmaruensis | Onchidiopsis pacifica |
| Onchidium | Onchidium ambiguum | Onchidium chameleon |
| Onchidium coriaceum | Onchidium nigricans | Onchidium patelloides |
| Onchidium peronii | Onchidium reticulata | Onchidium tonganum |
| Onchidium verruculatum | Onchidorididae | Onchidoris |
| Onchidoris bilamellata | Onchidoris depressa | Onchidoris diademata |
| Onchidoris diaphana | Onchidoris fusca | Onchidoris grisea |
| Onchidoris hystricina | Onchidoris inconspicua | Onchidoris luteocincta |
| Onchidoris muricata | Onchidoris oblonga | Onchidoris pusilla |
| Onchidoris sparsa | Onchidoris tenella | Onchium |
| Onchium conicaudatum | Onchium hawaiiense | Onchium metocellatum |
| Onchium ocellatum | Onchium robustum | Onchnesoma |
| Onchnesoma glaciale | Onchnesoma intermedium | Onchnesoma magnibatha |
| Onchnesoma magnibathum | Onchnesoma sarsii | Onchnesoma squamatum |
| Onchnesoma steenstrupii | Onchobothriidae | Onchocalanus |
| Onchocalanus affinis | Onchocalanus cristatus | Onchocalanus hirtipes |
| Onchocalanus latus | Onchocalanus magnus | Onchocalanus steueri |
| Onchocalanus trigoniceps | Onchocerca | Onchocerca alcis |
| Onchocerca cervicalis | Onchocerca cervipedis | Onchocerca flexuosa |
| Onchocerca gutturosa | Onchocerca stilesii | Onchocerca volvulus |
| Onchocercia | Onchocercias | Onchocerciasis |
| Onchocercidae | Onchocleidus | Onchocleidus ferox |
| Onchogamasus | Onchogamasus communis | Onchogamasus heterosetae |
| Onchogamasus pumilio | Onchogamasus quasicurtipilus | Onchogamasus virguncula |
| Oncholaimelloides | Oncholaimelloides vonhaffneri | Oncholaimellus |
| Oncholaimellus arcticus | Oncholaimellus brevicauda | Oncholaimellus calvadosicus |
| Oncholaimellus heterurus | Oncholaimellus labiatus | Oncholaimellus mediterraneus |
| Oncholaimellus meteori | Oncholaimellus vonhaffneri | Oncholaimidae |
| Oncholaimium oxyure | Oncholaimium priapulus | Oncholaimoides |
| Oncholaimoides elongatus | Oncholaimoides rugosus | Oncholaimoides striatus |
| Oncholaimus | Oncholaimus acuticauda | Oncholaimus aegypticus |
| Oncholaimus apostematus | Oncholaimus appendiculatus | Oncholaimus aquaedulcis |
| Oncholaimus attenuatus | Oncholaimus bajulus | Oncholaimus brachycercus |
| Oncholaimus brachycerus | Oncholaimus brevicaudatus | Oncholaimus brevicaudiculatus |
| Oncholaimus brevisetosus | Oncholaimus campbelli | Oncholaimus campylocercoides |
| Oncholaimus chiltoni | Oncholaimus cobbi | Oncholaimus conicauda |
| Oncholaimus curvicauda | Oncholaimus demani | Oncholaimus domesticus |
| Oncholaimus dujardinii | Oncholaimus dujardinioides | Oncholaimus filicaudatus |
| Oncholaimus martini | Oncholaimus microdon | Oncholaimus monodon |
| Oncholaimus nigrocephalatus | Oncholaimus notolangrunensis | Oncholaimus notoxyuris |
| Oncholaimus opisthonchus | Oncholaimus oxyuris | Oncholaimus parachiltoni |
| Oncholaimus paraegypticus | Oncholaimus paralangrunensis | Oncholaimus paredron |
| Oncholaimus priapulus | Oncholaimus punctatus | Oncholaimus scanicus |
| Oncholaimus serratus | Oncholaimus skawensis | Oncholaimus spissus |
| Oncholaimus steinboecki | Oncholaimus steineri | Oncholaimus thalassophygus |
| Oncholaimus thysanouraios | Oncholaimus tobagoensis | Oncholaimus trichospiculum |
| Oncholaimus ushakovi | Oncholaimus vesicarius | Oncholaimus viridis |
| Onchomerus bipunctatus | Onchomerus pilicornis | Onchon |
| Onchopelma | Onchopelma brevifasciatum | Onchopelma irwini |
| Onchopelma karooanum | Onchopelma majus | Onchopelma nitidum |
| Onchopelma pulchellum | Onchopelma trilineatum | Onchoporella |
| Onchoporella buskii | Onchoporella selenoides | Onchoporoides |
| Onchoporoides moseleyi | Onchoptera vidua | Onchorhinus |
| Onchorrhychus mykiss | Onchorynchus mykiss | Onchoscelis |
| Onchotelson | Onchotelson brevicaudatus | Onchotelson spatulatus |
| Onchulidae | Onchulus | Onchulus longicauda |
| Onchulus longicaudatus | Onchulus nolli | Oncicola |
| Oncicola angolensis | Oncicola bursata | Oncicola campanulata |
| Oncicola canis | Oncicola chibigouzouensis | Oncicola confusus |
| Oncicola dimorpha | Oncicola fraterna | Oncicola freitasi |
| Oncicola gigas | Oncicola justatesticularis | Oncicola lamasi |
| Oncicola luehei | Oncicola machadoi | Oncicola macrurae |
| Oncicola malayanus | Oncicola martini | Oncicola megalhaesi |
| Oncicola michaelseni | Oncicola micracantha | Oncicola oncicola |
| Oncicola paracampanulata | Oncicola pomatostomi | Oncicola schacheri |
| Oncicola signoides | Oncicola skrjabini | Oncicola spirula |
| Oncicola travassosi | Oncicola venezuelensis | Oncideres |
| Oncideres (lochmacodes) fasciata | Oncideres (lochmacodes) vermiculata | Oncideres (lochmaeocles) callidryas |
| Oncideres (lochmaeocles) sparsa | Oncideres (lochmaeocles) tesselatus | Oncideres (lochmaeocles) tessellatus |
| Oncideres (lochmaeodes) attenuata | Oncideres (lochmaeodes) callidryas | Oncideres (lochmaeodes) callidryas var. batesi |
| Oncideres (lochmaeodes) congener | Oncideres (lochmaeodes) fasciata | Oncideres (lochmaeodes) marmorata |
| Oncideres (lochmaeodes) pustulata | Oncideres (lochmaeodes) sladeni | Oncideres (lochmaeodes) sparsa |
| Oncideres (lochmaeodes) tessellata var. vestita | Oncideres (lochmaeodes) tessellatus var. conferta | Oncideres (lochmaeodes) vermiculata |
| Oncideres (lochmoeodes) fasciata | Oncideres (oncideres) aegrota | Oncideres (oncideres) alicei |
| Oncideres (oncideres) amputator | Oncideres (oncideres) bouchardi | Oncideres (oncideres) candida |
| Oncideres (oncideres) cephalotes | Oncideres (oncideres) cervina | Oncideres (oncideres) chevrolati |
| Oncideres (oncideres) crassicornis | Oncideres (oncideres) dalmani | Oncideres (oncideres) dejeani |
| Oncideres (oncideres) diana | Oncideres (oncideres) digna | Oncideres (oncideres) fabricii |
| Oncideres (oncideres) frontalis | Oncideres (oncideres) fulva | Oncideres (oncideres) fulvostillata |
| Oncideres (oncideres) germari | Oncideres (oncideres) gibbosa | Oncideres (oncideres) guttulata |
| Oncideres (oncideres) gutturator | Oncideres (oncideres) humeralis | Oncideres (oncideres) impluviata |
| Oncideres (oncideres) jatai | Oncideres (oncideres) limpida | Oncideres (oncideres) macra |
| Oncideres (oncideres) maculosa | Oncideres (oncideres) miliaris | Oncideres (oncideres) miniata |
| Oncideres (oncideres) minuta | Oncideres (oncideres) ocellaris | Oncideres (oncideres) ocularis |
| Oncideres (oncideres) ocularis var. argus | Oncideres (oncideres) pectoralis | Oncideres (oncideres) pittieri |
| Oncideres (oncideres) poecila | Oncideres (oncideres) pulchella | Oncideres (oncideres) pustulatus |
| Oncideres (oncideres) putator | Oncideres (oncideres) quercus | Oncideres (oncideres) repandator |
| Oncideres (oncideres) rhodosticta | Oncideres (oncideres) saga | Oncideres (oncideres) satyrus |
| Oncideres (oncideres) schreiteri | Oncideres (oncideres) scitula | Oncideres (oncideres) senilis |
| Oncideres (oncideres) stillata | Oncideres (oncideres) trinodata | Oncideres (oncideres) tuberculata |
| Oncideres (oncideres) ulcerosa | Oncideres (oncideres) ulcerosa var. vicina | Oncideres (oncideres) voeti |
