Additional morphological characters of the nematode Capillostrongyloides fritschi (Travassos, 1914) Moravec, 1982 (Nematoda: Capillaridae) from Bagrus spp. (Bagridae) inhabiting Damietta Branch of the River Nile, Egypt with a special reference to evaginated cirrus

The catfish Bagrus bajad (Forsskål) and B. docmak (Forsskål) (Siluriformes: Bagridae) are well distributed in the River Nile and have an economic value with good marketing and use in aquaculture. Collected specimens of Capillostrongyloides fritschi (Travassos 1914) were redescribed using a phase-contrast microscope and scanning electron microscope. The most remarkable finding was the unique structure of the evaginated cirrus, being composed of a proximal long tube, a middle spherical bulb packed with mature spermatozoa, and a distal funnel-shaped structure. All regions of the cirrus are provided with longitudinal and transverse muscles and covered with transverse cuticular folds. The mechanism of cirrus emergence was discussed based on available musculature data. Other important findings are the short stylet of the mouth, the two lateral oral lobes, 6-10 buried cephalic papillae and the bacillary bands that lack elevations. Stichosome is formed of 35-44 stichocytes that were differentiated into black and white forms, each containing dense granules and translucent vacuoles. The intestine showed a convoluted part at its anterior region. The vulvar lips are slightly elevated, many mature eggs are cleaved, and their shells are 3-layered. The anus was found in a groove bounded by two unequal lobes.