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|Ventral view of male with female positioned laterally within the gynecophoric chamber. (Scale bar: 200µm)|
Griphobilharzia amoena is a significant trematode that infect crocodiles such as the Australian freshwater crocodile, Crocodylus johnstoni, located in Darwin, Australia with reported illness in Irian Jaya as well (Platt, Blair et al., 1991). They possess a distinctive tegument that is composed of two lipid bilayers instead of a single bilayer. The double bilayer may be an adaptation to survive the host’s immune response (McLaren, 1977).
The life cycle remains unknown but cercariae probably develop in mollusks, most likely gastropods. (Smith, 1972). G. amoena are dioecious and are found in the circulatory system of their definitive host, C. johnstoni.
The male has a gynecophoric chamber that extends two-thirds of the acetabulum to testis. Interestingly, females are oriented anti-parallel to the males and are completely enclosed in the gynecophoric chamber. The nature of the physical relationship between the sexes is unclear. The worms are hematophagous, blood feeding, even the female despite being fully enclosed (Platt, Blair et al., 1991).
The notion that G. amoena is the only schistosome found in a cold-blooded animal (crocodile), leads to the hypothesis that perhaps G. amoena and other schistosomes are based in ectothermic archosaurs (Brant and Loker, 2000). It was also predicted that since G.amoena originated in ectotherms and then inhabited endothermic avian species, which is where they exist today (Brant and Loker, 2000). Brant and Loker used endothermy as a key factor in the diversification of schistosomes. However, upon analysis it was discovered that G.amoena is actually more closely related to spirorchiids from freshwater turtles rather than to schistosomes (Brant and Loker, 2000).
Brant, S. V., and Loker, E. S. 2005. Can specialized pathogens colonize distantly related hosts? Schistosome evolution as a case study. Public Library of Science Pathogens 1: 38.
McLaren, D. J., Hockley, D. J. 1977. Blood flukes have a double outer membrane. Nature 269: 147–149.
Platt TR, Blair D, et al. 1991. Griphobilharzia amoena n. gen., n. sp. (Digenea: Schistosomatidae), a parasite of the freshwater crocodile Crocodylus johnstoni (Reptilia: Crocodylia) from Australia, with the erection of a new subfamily, Griphobilharziinae. Journal of Parasitology 77:65–68.
Smith, J. W. 1972. The blood flukes (Digenea: Sanguinicolidae and Spirorchidae) of cold-blooded vertebrates and some comparison with the schistosomes. Helminthological Abstracts Series A 41:161–204.