The Calicotyle conundrum: do molecules reveal more than morphology?

Partial large subunit 28S rDNA sequences were obtained for specimens of Cal icotyle (Monogenea: Monocotylidae) from eight different host species distri buted worldwide to test the validity of some species and to address the que stion of host-specificity in others. Sequences obtained for Calicotyle spec imens identified as C. kroyeri based on morphological methods from the type -host Raja radiata (Rajidae) and an additional host R. clavata, both from t he North Sea, were identical. However, 'C. kroyeri' from the cloaca of R. n aevus from Tunisia, Raja sp. A from Tasmania and R. radula from Tunisia dif fered from C. kroyeri from R. radiata by five (0.51%), 21 (2.13%) and 39 (3 .96%) base pairs, respectively, over 984 sites. Therefore, it is likely tha t the specimens from Raja sp. A, R. radula and perhaps even from R. naevus are not C. kroyeri. Molecular results determined that the calicotylines fro m the cloaca of Urolophus cruciatus and U. paucimaculatus (Urolophidae) fro m southern Tasmania identified previously as C. urolophi are indeed identic al. Large subunit 28S rDNA sequences of C. palombi and C. stossichi collect ed from the cloaca and rectal gland, respectively of Mustelus mustelus (Tri akidae) from the coast of Tunisia differ sufficiently for these calicotylin es to be considered separate and valid species. Our results indicate that s ome species of Calicotyle are not strictly host-specific, but that C. kroye ri may not be as widely distributed in rajids as was believed previously. C alicotyle specimens from rajids must be re-examined critically to determine whether there are morphological differences indicative of specific differe nces that may have been overlooked previously.