Pigmentation patterns are useful for species identification of third-stage larvae of gnathiids (Crustacea: Isopoda) parasitising coastal elasmobranchs in southern Japan
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Previous studies from southern Japan reported larval stages of eight gnathiid isopod species parasitising coastal elasmobranchs. Since gnathiid larvae of these different species closely resembled each other, it was necessary to obtain specimens of free-living adult males for identification to the species level. This was achieved by allowing larvae of the final stage to moult into adult males. From these males, specimens of a species new to science were discovered and described here as Gnathia rufescens n. sp. The main differentiating characteristics of G. rufescens n. sp. are: (i) the apex of pleotelson is oval shaped; (ii) the dorsal sulcus is wide in the posterior part; and (iii) the article 3 of the pylopod is not reduced in the male. Additionally, this paper summarises the specific pigmentation patterns of third-stage larvae of the new species and eight previously described species. Furthermore, host records and host use by the gnathiids were summarised based on data from 158 hosts and over 4,500 gnathiid samples; these are discussed with a focus on host-specificity of the nine gnathiid species studied.
KeywordsDistal Margin Plumose Seta Pigmentation Pattern Disk Width Internal Margin
Part of the material examined in this study was collected during the KUMEJIMA 2009 Expedition organized by the Transdisciplinary Research Organization for Subtropical and Island Studies of the University of the Ryukyus, the Center for Marine Bioscience & Biotechnology of the National Taiwan Ocean University, the Raffles Museum of Biodiversity Research of the National University of Singapore, and the Biodiversity Research Center of the Academia Sinica. The expedition operated under a permit granted to Dr. T. Naruse by the Okinawa Prefectural Governor and the Kumejima Fisheries Cooperative. This study was partly supported by a Grant-in-Aid JSPS Fellows (No. 23–527). I would like to thank two anonymous reviewers for their valuable comments.
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