The life-cycles and larval development of some acanthocotylids (Monogenea) from Plymouth rays

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Abstract
Acanthocotylid (monogenean) parasites inhabit the skin of rays, and the lack of cilia on the infective larvae of these parasites may be an adaptation to the host's bottom-living habits.Freshly hatched larvae must remain on the sea-bottom until a ray settles on top of them, when the larvae then have the opportunity to attach themselves to the host's ventral surface. Acanthocotyle lobianchi, which infects Raia montagui and R. clavata at Plymouth, becomes sexually mature on the host's ventral surface and rarely wanders from it, but A. elegans, which is found on R. clavata only, migrates to the dorsal surface of the host before reaching sexual maturity.The larvae of acanthocotylids use their haptoral hooklets to attach themselves to the host's epidermis, but as the parasites increase in size the load on these hooks becomes acute. This load is relieved not as in other monogeneans by the development of hamuli but by the transformation of the posterior third of the larval body into an accessory ‘pseudohaptor’.I am obliged to the Director and Staff of the Plymouth Laboratory for laboratory facilities and to Mr J. E. Green for his interest and help on many occasions.
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