"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

November 11, 2011

Polypocephalus sp.

Today's parasite might be thought of as an "aquatic Toxoplasma" in that it also induces behavioral changes in its hosts. Polypocephalus is a genus of tapeworms that infects both shrimp (Litopenaeus setiferus) and then likely rays such as the Atlantic stingray, (Dasyatis sabina). The larvae of the cestode invade the neural tissue of the shrimp hosts, particularly in the abdominal ganglia. Studies recently showed that the more larval tapeworms a shrimp had, the more time these hosts spent walking on the substrate, as opposed to sitting still or swimming. Although the authors had predicted that they would see an increase in swimming behavior because that might expose them to predation more readily, perhaps just the increased activity in general is enough to promote transmission. Nonetheless, this was an exciting insight into a potentially new system for studying parasite manipulation of their hosts.

Source: Carreon, N., Z. Faulkes, and B. L. Fredensborg. 2011. Polypocephalus sp. infects the nervous system and increases activity of commercially harvested shrimp. Journal of Parasitology 97:755-759

Image from figure of that paper.


  1. I think rays are bottom feeders, so it would be easier for them to catch a walking shrimp than a sitting or swimming shrimp ...