"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

June 7, 2010

June 7 - Diplozoon paradoxum

We normally think of parasites as rather despicable creatures - out for food and shelter and not caring who suffers in their quest. But today's parasite, the monogenean Diplozoon paradoxum, has at least one redeeming quality - it just might be the most monogamous organism on the planet. A young D. paradoxum, called a diplora, settles down on the gills of a fish and waits for a mate. If another one never comes along, then the single parasite will simply die (of loneliness?). However, if another comes along, the two worms actually fuse their bodies completely together and become adults, with one producing testes and the other producing ovaries allowing them to continually cross-fertilize. And that is how they will stay - forever.

Diplozoon is the official symbol of the Meguro Parasitological Museum in Japan - if you visit, you can even buy jewelry featuring the conjoined parasites.

The image comes from this site.


  1. Been there - indeed, it was the only place in Tokyo that I was really enthusiastic about visiting :D

  2. Re "might be the most monogamous organism"... What about Echiurans and angler fish? Perhaps obligately autogamous plants like Epipactis helleborine are truly the most monogamous.

  3. What I like about this relationship is you can still see that they were two worms - that even though they are fused, they still retain some of their own identity. It's a symmetry.

  4. Hmm now I need to make a pick up line around this worm to attract my own eternally bonded parasite:p

  5. There is a book called Parasite in Love, by Miaki Sugaru, which main topic is the mind-controling parasites. In this book, the main character likes to talk about parasites and mentions D. Paradoxum. It is said that one of the fishs inhabited by D. paradoxum is the carp Koi, word that means "love" in japanese. She also says that the parasite discard the eyeballs of the carp within 24 hours, so Koi, like love, is blind. It is such a beautiful and romantic analysis, considering that D. paradoxum blindly joins the first of his type that he meets and never leaves him, though he is hermaphrodite and can self copulate. However its behavior probably has nothing to do with love. Yet we can dream and pretend it has.