Surface ultrastructure and the mitochondrial gene rrnl of Parachristianella indonesiensis Palm, 2004 (Trypanorhyncha: Eutetrarhynchidae) with the amended generic diagnosis.

The microthrix pattern of adult Parachristianella indonesiensis Palm, 2004 is described for the first time based on the standardized terminology for microtriches, and the generic diagnosis of Parachristianella Dollfus, 1946, regarding microtriches, is also amended. The surface ultrastructure of P. indonesiensis consists of three kinds of microtriches so that the proximal and distal bothrial surfaces are covered respectively with acicular to short capilliform filitriches and aristate gladiate spinitriches interspersed with capilliform filitriches. The remainder of the scolex bears capilliform filitriches. The surface of the proglottid is adorned with acicular filitriches. There was no significant difference in the length of the capilliform filitriches covering the different parts of the scolex peduncle. For the first time, the uniciliated papillae adorned with filitriches as sensory receptors are reported from this parasitic species. The partial rrnl of P. indonesiensis is also presented as the only known sequence of this gene in the superfamily Eutetrarhynchoidea Dollfus, 1969. The pairwise comparisons of rrnl between P. indonesiensis and the trypanorhynch species for which rrnl sequence is available were in accordance with the last phylogeny presented for the order Trypanorhyncha. The infection parameters (prevalence, mean abundance, and mean intensity) of P. indonesiensis parasitizing Pastinachus sephen (Forsskål) from the eastern Persian Gulf were also compared during approximately 5 years, and no significant differences were observed. This may be interpreted as the stability of the factors playing important roles in the life cycle of P. indonesiensis in the eastern Persian Gulf during this period.