Pentastomids are a group of parasites that primarily infect the respiratory tracts of reptiles and amphibians, with a few species that infect birds and mammals (see Armillifer agkistrodontis). While they might look like worms, pentastomids are more closely related to arthropods, and they are ubiquitously found in the lungs of crocodiles. In fact, it's quite likely that every single species of living crocodilians is infected with pentastomids, indicating that these two groups have had a long co-evolutionary history which stretches back millions or possibly even hundreds of millions of years.
Today's parasite is Agema silvaepalustris and it is found in the lungs of the dwarf crocodile Osteolaemus tetraspis, which lives in the equatorial rain forest zone of West and Central Africa. The crocodiles become infected when they eat fish that possess the larval instars of A. silvaepalustris. The lungs of an individual crocodile can be infected with a few dozen to over a hundred of these parasites, and it is amazing to think that these weird little banana-shaped critters are more closely related to shrimps and crabs than any actual "worm"!
For further details, see:
Riley, J., Hill G. F., Huchzermeyer, F. W. (1997) A description of Agema, a new monotypic pentastomid genus from the lungs of the African dwarf and slender-snouted crocodiles. Systematic Parasitology 37: 207-217.
Contributed by Tommy Leung.