Abstract
A new sexannulate species of the genus Orobdella Oka, 1895, Orobdella mononokesp. n., is described on the basis of five specimens collected from Yakushima Island, Japan. Orobdella mononokesp. n. differs from other sexannulate Orobdella species in its possessing the following combination of characters: dorsal surface bicolor in life, I-XIII, XXVII and caudal sucker grayish purple, XIV-XXVI amber, male gonopore at XI c11/c12, female gonopore at XIII b2, 8 + 1/2 between gonopores, tubular but bulbous at junction with crop gastroporal duct, epididymides in XV-XIX, and atrial cornua ovate. Phylogenetic analyses using nuclear 18S rDNA and histone H3, and mitochondrial COI, tRNA(Cys), tRNA(Met), 12S rDNA, tRNA(Val) and 16S rDNA markers show that Orobdella mononokesp. n. is closely related to Orobdella esulcata Nakano, 2010 from Kyushu, Japan, and two species, Orobdella dolichopharynx Nakano, 2011 and Orobdella shimadae Nakano, 2011, from the Ryukyu Archipelago, Japan.