Morphology and development of the haptors among the Monocotylidae (Monogenea)

Monocotylid monogeneans inhabit a wide diversity of sites on their chondric hthyan hosts including the skin, Sills, nasal fossae, urogenital system and coelom. The large variation in the morphology of the haptor appears to ref lect this diversity in attachment sites. We demonstrate that the complexity of the haptor can be related to the habitat of the parasite. Generally, th ose parasites which live in habitats subject to strong water currents such as the gills and dorsal skin surface have more complex haptors than those i n environments exposed to weaker or no water currents including the nasal f ossae, urogenital system and body cavity. However, there can be considerabl e variation in haptoral components, even among congeners, living on the 'gi lls' of their hosts. The microhabitat was determined for Monocotyle helicop hallus and M. spiremae, both from the gills of the pink whipray, Himantura fai, and M. corali from the gills of the cowtail ray, Pastinachus sephen. W e demonstrate that differences in the morphology of the hamuli and the numb er and morphology of septal sclerites and marginal papillae among these spe cies of Monocotyle can be related directly to their microhabitat. It also a ppears that different haptoral structures are important for attachment to t he host at different stages in the development of the parasite, based on st udies on the development and distribution of Neoheterocotyle rhinobatidis f rom the gills of the common shovelnose ray Rhinobatos typus.