الفهرس 
INTRODUCTION
Feeding habitsOnly 14 pages are availabe for public view
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Abstract
In Egypt, Barboronia assuti and Salifa delicata, (Arhynchobdellida) are the most abaundant leeches in freshwater canals. During November 2008 to May 2009, when water temperature ranged between 15 and 25 °C, both of Barbronia assiuti and Salifa delicata were collected from Al-Sont canal near Assiut city. In the laboratory, the leeches examined for discover the parasites. Three parasites were obtained Epistylis sp, Saprolegnia hypogyna and Nosema sp. About 80% of total collected leeches were infected with the peritrich ciliate Epistylis sp., the infection occurred in the field. Both light and scanning electron microscopy showed the morphology of this parasite which attached to the surface of the leech body by a stalk. Histopathological studies revealed the necrotic lesions at sites of infection. The leech body seemed to be sloughy. These lesions appeared as the damage of cuticle, epidermis, and dermis of the leech body wall. Presence of this parasite in high numbers covering large areas of the body can impede gas exchange leading to leech suffocation and finally its death. Like, the other sessile ciliates, Epistylis sp. feed on bacteria and suspended organic debris, which are prevalent in nutrient-rich water, hence, Epistylis is a good indicator of poor water quality (pollution).
In the laboratory, 94% of total collected leeches showed signs of oomycotal infection (cotton–wool like appearance radiating out in whorled pattern) and died within 3 days of collecting time. Direct microscopy and culture proved Saprolegnia hypogyna was the pathogen. Histopathological studies showed necrotic lesions, as destruction of cuticle, epidermis, dermis, muscle layers, botryoidal tissue and even the gut with the oomycete hyphae penetrating the damaged tissues. The third pathogen is the endoparasite Nosema sp, which was discovered when less viable individuals of Salifa delicata were examined and seemed to be healthy. Smears, serial paraffin sections, scanning and transmission electron microscopy demonstrated the presence of microsporidian spores. Histopathological study showed some pathological effects as the destruction of the epidermis, dermis and muscle layers, presence of numerous irregular pigments distributed within the connective tissue (granuloma) and presence of vesicles within the connective tissue (vesiculation). Tissue reactions, against the invaded endoparasite, revealed the presence of fibrous membrane surrounded the adult spores (encapsulation) to restrict the distribution of the spores, migration of chromatophores and fibrocytes from the body wall and connective tissue to surround the capsules, proved several signs of pathogenecity.