A new species of the genus Johanssonia Selensky, 1914 (Hirudinea: Piscicolidae) collected in the Kuril-Kamchatka Trench at the greatest depth ever recorded for fish leeches

摘要

Johanssonia extrema n. sp. was described from a depth of 8728.8 m in the Kuril-Kamchatka Trench. The leech is elongate, up to 58 mm total length. Body is smooth, lacking papillae, tubercles, pigmentation, eyes and ocelli. Suckers are well-developed, eccentrically attached. Lateral pulsatile vesicles are present. Posterior crop caeca are fused. The male reproductive system is characterised by six pairs of testisacs, elongate, tubular atrial cornua and ejaculatory ducts, and coiled seminal reservoirs. The female reproductive system has ovisacs with oviducts looping back anteriorly and a well-developed conductive tissue mass. A possible fish host is the Pacific grenadier Coryphaenoides acrolepis (T. H. Bean, 1884). The molecular phylogenetic analysis revealed sister relationships between the new species and the boreal-arctic fish leech Johanssonia arctica (Johansson, 1898).