CHARACTERIZATION OF FASCIOLA-HEPATICA REDIAL GENERATIONS BY MORPHOMETRY AND CHAETOTAXY UNDER EXPERIMENTAL CONDITIONS

Morphometric and chaetotactic studies were carried out on the body and cephalic regions of the rediae of Fasciola hepatica (Trematoda: Fasci olidae) in order to precisely identify the different redial generation s of this trematode in Lymnaea truncatula under experimental infection . At day 49 post-exposure at 20 degrees C, the length of the redia was significantly higher in the first group of the first generation (R1a) compared with successive generations, Rib, R2a and R2b/R3a. The width of the body was similar in the R1a, Rib, and R2a rediae, but was sign ificantly lower in the R2b/R3a groups. The intrapharyngeal cavity of R 1a rediae was significantly wider compared with the Rib, R2a, and R2b/ R3a groups, whereas the pharyngeal wall was significantly thicker in t he R2b/R3a rediae compared with the Rib and R2a groups. Four other mea surements, namely the maximum length and width of the pharynx, diamete r of the mouth, and width of intestine, also showed significant variat ions in relation to pharyngeal morphology and age of infection. Discri minant analysis based on these measurements demonstrated that 98% of t he rediae were readily categorized into the four groups identified. Th e number of perioral sensillae ranged from 126 to 160 but a significan t difference was only noted between the mean values of the first gener ation and those of the group R2b/R3a. From these parameters, the maxim um width of the pharyngeal lumen was found to be the best characterist ic in the identification of the redial generations.