Comparative morphology of Gyrodactylus groenlandicus Levinsen, 1881, G. nainum Hanek and Threlfall, 1970, G. pleuronecti Cone, 1981, and G. adspersi sp. n. (Monogenea) from northwest Atlantic fishes

Abstract

Gyrodactylus groenlandicus from Myoxocephalus scorpius, G. nainum from Myoxocephalus quadricornis, G. pleuronecti from Pseudopleuronectes americanus, and Gyrodactylus adspersi sp. n. from Tautogolabrus adspersus, collected from the northwest Atlantic Ocean, are compared morphologically. Gyrodactylus groenlandicus has long hamuli (63–66 μm) and long marginal hooklets (35–36 μm). Gyrodactylus nainum and G. pleuronecti have intermediate-sized hamuli (56–58 and 55–59 μm, respectively); the marginal hooklets of G. nainum are 35–36 μm in length while those of G. pleuronecti are 28–29 μm. Gyrodactylus adspersi sp. n. has short hamuli (38–43 μm) and short marginal hooklets (24–27 μm). The four species differ subtly, but distinctly, in morphology of the marginal hooklet sickle. The study concludes with discussion of possible evolutionary relationships between the four species.