Distribution of Holtodrilus truncatus, a Branchiobdellidan Ectosymbiotic on Atyid Shrimps in the Kii Peninsula, Western Japan, with Reference to Salinity Tolerance and Host Preference.

The distribution of the branchiobdellidan Holtodrilus truncatus (Liang, 1963), which is symbiotic on atyid shrimps, was surveyed in 26 river catchments, covering almost all of the Kii Peninsula, western Japan. Holtodrilus truncatus has been recorded in 10 rivers located from the southwest to northeast regions of the peninsula. Paratya compressa was the dominant host species in all rivers, with a lower prevalence on Caridina leucosticta, C.