Praobdellidae (Hirudinida: Arhynchobdellida) is not specific only to the mucous-membrane after all: Discovery of a praobdellid leech feeding on the Japanese freshwater crab Geothelphusa dehaani.

Praobdellid leech species have been known to infest vertebrate mucous-membrane; some of them have been assumed to be invertebrate bloodsuckers. Praobdellid individuals were found feeding on the Japanese freshwater crab, Geothelphusa dehaani, at Mt. Tsukuba, Ibaraki Prefecture, Japan. The leech had inserted its head into the intersegmental membrane between the crab's carapace and legs. Our findings represent a first invertebrate host record for praobdellid leeches. Additionally, molecular phylogenetic trees based on nuclear 18S and 28S rRNA, mitochondrial cytochrome c oxidase subunit I, and 12S rRNA sequences as well as the leech morphological characteristics showed that the present leech might belong to an unrecognized praobdellid lineage: a taxonomic revision of the Japanese praobdellid species is needed.