Distribution of ectosymbiotic species of Cirrodrilus (Annelida, Clitellata, Branchiobdellida) in northern Japan, with notes on their taxonomy

要旨

Twelve species of Cirrodrilus, a genus of ectosymbiotic branchiobdellidans, have been recorded on the Japanese crayfish, Cambaroides japonicus, from the islands of Hokkaido and northern Honshu. To clarify the geographic distribution of these species, we examined branchiobdellidan assemblages from 71 locations on Hokkaido and 59 on northern Honshu. We found 11 morphologically distinct species. The following 8 species: Cirrodrilus digitatus, Ci. cirratus, Ci. uchidai, Ci. sapporensis, Ci. nipponicus, Ci. japonicus, Ci. megalodentatus and Ci. homodontus were exclusively recorded from Hokkaido, while Ci. aomorensis was restricted to Honshu. Two other species, Ci. tsugarensis and Ci. iwakiensis, had previously only been recorded from Honshu but were now also found on Hokkaido. The anomalous record of Ci. digitatus and Ci. uchidai on Honshu is known to be the result of crayfish being translocated from Hokkaido. No significant difference in the species composition was found between eastern and western regions on Hokkaido, where divergent lineages have been detected in the Japanese crayfish host. Overlaps in the diagnostic characters of Ci. cirratus and Ci. uchidai suggest that both taxa belong to either a single species or form a species complex.

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