Rotifers parasitic on, [227]

Oligocladus, [19], [22]

Oligognathus, [297]

Ollulanus, [142];

O. tricuspis, [144], [161]

Omalostoma, [49]

Onchnesoma, [422], [423], [426], [430], [447]

Onchocotyle, [73]

Oncholaimus, [157]

Onchosphaera-larva of Cestodes, [87], [88]