Invasion of the shovelnose ray (Rhinobatos typus) by Neoheterocotyle rhinobatidis and Merizocotyle icopae (Monogenea: Monocotylidae).

This study examined the route of infection by free-swimming larvae of 2 monocotylid monogeneans that inhabit the gills (Neoheterocotyle rhinobatidis) and the nasal tissue (Merizocotyle icopae) of the shovelnose ray, Rhinobatos typus, from Heron Island on the Great Barrier Reef, Australia. Larvae of N. rhinobatidis and M. icopae attached directly to the gills and the nasal tissue of the ray, respectively, and did not first settle on the skin. Initial development of the post-oncomiracidium of N. rhinobatidis was rapid and hamuli formed between 6 and 24 h p.i. at a mean temperature of 26 degrees C. However, growth then slowed markedly and was variable; only 2 fully mature individuals were found 20 days p.i. at a mean temperature of 24.5 degrees C. Development of M. icopae was slow and variable throughout; hamuli did not appear until 10 days p.i. and no mature individuals were obtained even 22 days p.i. at a mean temperature of 24.5 degrees C. No character could be found as an indicator of parasite age for N. rhinobatidis or M. icopae due to the high variability in development in both species.