Bilharziosis Roundworm -Schistosomum haematobium
For all the awful things bilharziosis (or schistosomiasis, depending on your region of the world) does, their reproduction is almost endearing. The female is a “normal”, worm-like shape, but the male is shaped almost like a boat or trough. Once the nematodes reach adulthood, they seek out another of their kind (as they can only reproduce sexually), and pair up. Once paired up, the female nestles into the trough of the male, and the male takes over feeding for both of them. Though they never fully merge (like the anglerfish male does with the female), they can remain together for years, with the female producing their eggs, and the male feeding them both. It’s almost cute.
Bilharziosis. Frank Cole Madden, 1907.