Two new polystomes (Monogenea: Polystomatidae) from the eyes of North American freshwater turtles

Neopolystoma moleri n. sp. and Neopolystoma grossi n. sp. are described as new polystome species on the eyes of Apaloneferox and Pseudemys concinna floridana, respectively from Florida, USA. Eleven other polystome species are currently knownfrom chelonian hosts in the USA, but only Neopolystoma elizabethae and Neopolystoma fentoni were described from the eye.Ocular polystomes are characterized as having spindle-shaped eggs; an exceptionally firm grip on the host; as well as the abilityto stretch, which gives them the advantage of being stationary while extending to feed, reducing the risk of being dislodged.The two new species can be distinguished from known Neopolystoma species by a combination of characteristics including marginal hooklet morphology.

Ultrastructure of musculature of the marginal hooklets of Macrogyrodactylus congolensis, a monogenean skin parasite from the catfish Clarias gariepinus

The musculature of the marginal hooklets of adult Macrogyrodactylus congolensis (Prudhoe, 1957) Yamaguti, 1963 has been studied. Each marginal hooklet of M. congolensis is associated with three pairs of muscles. The possible role of these muscles in the operation of the marginal hooklet is discussed. Transmission electron microscopy has been used for the first time to study the marginal hooklets of M. congolensis. The handle articulates with the blade in the region of the guard. Internally, the handle, the proximal region of the blade in the articulation region and the distal pointed region of the blade consist of three layers. Distal to the articulation region, the blade consists of four layers with differing electron densities. A cavity is associated with the distal region of the blade and the handle. A cyton containing secretory bodies of different sizes and shapes was found in association with each marginal hooklet. The possible function of these secretions is discussed.

Synonymization of Gyrodactylus labradorius Hanek and Threlfall, 1970 with G. bairdi Wood and Mizelle, 1957 (Monogenea)

This study compares Gyrodactylus bairdi Wood and Mizelle, 1957 from Cottus bairdi Girard in Indiana and C. cognatus Richardson in the Yukon Territory to G. labradorius Hanek and Threlfall, 1970 from C. bairdi in Labrador. The marginal hooklet sickles in the two species are identical in shape and size. The hamuli are similarly shaped and slight differences in overall size of the haptoral sclerites can be attributed to intraspecific variation. It is concluded that G. labradorius is a synonym of G. bairdi, and that G. bairdi, so consolidated, is distributed throughout most of the geographical range of freshwater cottids in North America.

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

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.