April 21 - Cyamus ovalis

Some of you might be familiar with the New Zealand movie "Whale Rider" - well, the parasite featured today is a real whale rider.

Cyamus ovalis belongs to a family of crustaceans call Cyamidae that specialize as ectoparasites of cetaceans. Despite being called "lice", whale lice are actually amphipods, and unlike most amphipods (such as sand hoppers or "scuds") which have bodies that are laterally flattened (narrower when viewed from top), the whale lice have dorsally flattened bodies, like a crab, better suited to the life-style of clinging onto the surface of an oceanic behemoth. Because of their lack of free-swimming stages, whale lice can only be transferred from whale to whale on contact. As a result, they have a very close co-evolutionary relationship with their host, and different species of cetaceans have different species of whale lice

Whale lice have been used to track the population genetic structure of their whale hosts. In the case of Cyamus ovalis, their hosts are the right whales Eubalaena spp. Swarms of C. ovalis cover the raised pieces of roughened skin (call callosities) on the head of the whale. Studies into their population genetic structure have revealed that, just like their whale hosts, the Northern and Southern Hemisphere populations of lice have been isolated from each other for several million years.

For more information, on the coevolution of whale lice with their host, see this link . The photograph for Cyamus ovalis was taken from the same webpage as the one above - Photo Credit: Vicky Rowntree, University of Utah.

There is also a trailer on YouTube for an upcoming documentary about researching whale lice. If this doesn't make being a parasitologist look like the most exciting career out there, what will?

Thanks to Tommy Leung for all of this.