"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.