Placentonema gigantisma
The largest nematode ever observed is Placentonema gigantisma, discovered in the placenta of a
sperm whale. This 8 meter long nematode is said to have 32 ovaries. The original reference (which I’ve
never seen) is Gubanov, N.M. 1951. Compt. Rend. Acad. Sci. URSS 77, 1123.
Other big verebrate parasites include Dioctophyma renale, the giant kidney worm (1m x 1.5cm).
Most plant parasites are considerably smaller, usually measuring around 1 mm or less. Several
Longidorus species exceed 10mm in length.