Comparative electron microscope studies on the epidermis of the blood living juvenile and gill living adult stages of Amphibdella flavolineata (Monogenea) from the electric ray Torpedo nobiliana

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Abstract
SUMMARY: The covering layer of Amphibdella flavolineata has been found to be a syncytial cytoplasmic epidermis bearing scattered microvilli and connecting with parenchymally situated ‘cell’ bodies or cytons by means of conspicuous, microtubulelined cell processes. There was no evidence from a comparison of the covering epidermis of the juvenile blood living form and that of the gill living adult that this layer in the juvenile was especially modified for life in the host blood system.The epidermis of adult and juvenile worms was found to be remarkably similar, the main difference being that that of the adult was slightly thicker and bears longer microvilli. Apart from some lamellate bodies of doubtful significance, the inclusions found in the epidermis of adult and juvenile forms were also very similar.The outer epidermis of the juvenile monogenean was found to be quite different from that of Schistosoma mansoni in that it is not permeated by incursive channels and contains many more mitochondria than the epidermis of the digenean. The epidermal cell bodies of Amphibdella tend to have electron-lucent areas especially in the ‘ apical cell’ regions leading to the cell processes that connect with the outer layer. Electron-dense granules secreted by the epidermal cells accumulate in these ‘clear’ regions before being transferred to the outer layer. There is some slight evidence that these electron-lucent regions may have contained glycogen. The epidermal ‘cell’ bodies of the juvenile tend to be multinucleate, whilst those of the adult are usually uninucleate.Thanks are due to the Director and staff of the Marine Biological Laboratory, Plymouth for providing accommodation and material. The assistance of Mr George Best of the Plymouth Laboratory and Mr Harry Edge of King's College London Botany Department, who maintain the microscopes used in this work, is especially appreciated.