Heduris spinigera is a species of parasitic nematode found in the stomach of a number of New Zealand's brackish water fishes. While this parasite was initially described decades ago, its lifecycle was only recently determined using a combination of both morphological and genetic identification techniques. This parasite uses a small crustacean as its intermediate host - the benthic amphipod Paracorophium excavatum. While this amphipod is consumed by many different species of fish, it seems that not all fish are equally suitable as hosts for H. spinigera. While their diets potentially expose them to H. spinigera, the nematode fails to become establish in these potential hosts, possibly due to factors such as host anatomy or physiology.
Like most parasites, H. spinigera is restricted to infecting a limited range of host species. Most parasites display some degrees of host specificity, and there are only very few parasites which can truly infect a wide range of different hosts. We now know that many species of parasites, which were previously believed to be host generalists, are actually cryptic species complexes, composed of morphologically similar but genetically distinct species, each infecting a different species of host.
Luque, J.L., F.M. Vieira, K. Herrmann, T.M. King, R. Poulin, and C. Lagrue. 2010. New evidence on a cold case: trophic transmission, distribution and host specificity in Hedruris spinigera (Nematoda: Hedruridae). Folia Parasitologica 57: 223-231.
Contributed by Tommy Leung.
Link to paper here.