Vol. 24, No. 2, pp. 117-123 International Journal of Nematology December, 2014 117 First description of a nematode, Spinitectus gabata n. sp. (Spirurina: Cystidicolidae), from the deep sea oarfish, Regalecus russelii (Regalecidae) in Japan George Poinar, Jr.*, Sara B. Weinstein**, Ana E. Garcia-Vedrenne**, and Armand M. Kuris** *Department of Integrative Biology, Oregon State University, Corvallis, OR 97331, USA **Department of Ecology, Evolution and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA E-mail: poinarg@science.oregonstate.edu Abstract. Spinitectus gabata n. sp. (Spirurina: Cystidicolidae) from the gastrointestinal tract of an oarfish, Regalecus russelii, (Regalecidae), captured off the coast of Fukuoka Prefecture, Kyushu Island, Japan is the first nematode described from an oarfish. Diagnostic characters of the new species are: female length of 6.5-8.7 mm, well-developed submedian labia, psuedolabia with pointed apices, excretory pore positioned between spine rows 20 and 22, posterior position of vulva, large oval uterus, long spicule length of 710-1350 μm, wide, flattened, short, right spicule, 12:1 to 16:1 ratio between the length of the long and short spicules and 4 pairs pre-anal and 5 pairs post-anal genital papillae supported by narrow caudal alae. Unusual features such as the bifurcation of the long, left spicule and the short right spicule serving as a gubernaculum are discussed further. Keywords. Body spines, Cystidicolidae, gastrointestinal tract, Japan, new species, oarfish parasite, spicule modified as gubernaculum, Spirurina. INTRODUCTION ematodes comprising the 23 genera and some 140 species of the cosmopolitan family Cystidicolidae of the suborder Spirurina mainly parasitize the gastrointestinal tract of freshwater and marine fish. The life cycle of the few freshwater species that have been investigated indicates crustacean or insects as the intermediate and/or paratenic hosts. One genus in this family, Spinitectus Fourment, 1884, is characterized by a series of transverse, spine-bearing rings on the body, especially on the anterior portion (Skrjabin et al., 1949; Anderson, 2000; Caspeta-Mandujano et al., 2007). The present study describes a new species of Spinitectus recovered from the gastrointestinal tract of an oarfish, Regalecus russelii, (Regalecidae), collected off the coast of Fukuoka Prefecture, Kyushu Island, Japan and discusses some of its unusual morphological features. Oarfish are elongated, compressed, lampriform, deep sea fish that are rarely seen or captured even though they have a worldwide distribution in both temperate and tropical oceans (Roberts, 2012). Parasites of oarfish have been little studied and the only previous nematodes known from this host were juveniles of Contracaecum sp. Raillet & Henry, 1912 in an oarfish captured off the coast of California (Kuris et al., in Press). The nematode described below is the first parasite to be described from a member of the Regalecidae. MATERIALS AND METHODS Twenty five specimens of Spinitectus sp. were removed from the gastrointestinal tract of an oarfish, Regalecus russelii, (Regalecidae) captured off the coast of Fukuoka Prefecture, Kyushu Island, Japan (33°58'18.6"N 130°46'11.7"E) on 19 March, 2014. The total length of the oarfish was 440 cm. The gastrointestinal tract and gills were frozen prior to dissection for parasitological examination. Seventeen nematode specimens were fixed in either 70% ETOH or 10% formalin for study. Examination and photographs were made with a Nikon stereoscopic microscope SMZ-10-R at 80x and a Nikon Optiphot microscope at 1000x. Attempts to prepare EM scans were unfortunately unsuccessful. N