Suddenly we are all spending a lot more time thinking about our immune systems—but what about the immune systems of the animals around us? For a long time it was thought that only animals with jaws and vertebrates had lymphocytes, but research with sea lampreys suggests otherwise. Researchers found lymphocyte-like cells in the gut of these charming jawless fish that perform many of the same adaptive immune functions as our lymphocytes. 

Sketch and fact contributed by Amelia Munson

Source: Yuan, S., Tao, X., Huang, S., Chen, S. and Xu, A., 2014. Comparative immune systems in animals. Annu. Rev. Anim. Biosci., 2(1), pp.235-258.