The microthrix pattern of common forms of the trypanorhynch cestode Prochristianella clarkeaeBeveridge, 1990 on which the microscopically visible microtriches almost extended to the posterior end of the scolex was described using SEM and compared to other forms for which this pattern was different. The proximal bothrial surface and the scolex peduncle of all the examined specimens were covered with palmate spinitriches and papilliform filitriches. Unlike the common specimens of P. clarkeae, on the surface of those specimens with unusual distributions of microtriches as well as those on which the microscopically visible microtriches were not observable, palmate spinitriches extended to the mid-pars vaginalis and not to the posterior end of the scolex. Statistical tests did not detect any significant difference in the measurements of the specimens possessing different microthrix patterns. Furthermore, the partial 28S rDNA confirmed that the different forms were conspecific and that P. clarkeae possesses an intraspecific variation in the distribution of palmate spinitriches. Pastinachus sephen as a new host record was also established for Prochristianella clarkeae reported for the first time from the Persian Gulf.
We are grateful to Professor Ian Beveridge from the University of Melbourne for kindly giving the unpublished information related to the original description of Prochristianella clarkeae. We also thank Mrs. Eileen Harris and Dr. Peter D. Olson from the Natural History Museum in London for kindly giving the related information of the only specimen of P. clarkeae from which the molecular data was available. Professor Janine N. Caira from the University of Connecticut is gratefully thanked since she kindly examined, using light microscopy, the only specimen of P. clarkeae for which the molecular data had been earlier registered in NCBI.
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