Two new species of Tubificoides (Annelida: Clitellata: Naididae) from the Blake Ridge methane seep in the northwest Atlantic Ocean Sebastian Kvist, Jennifer Dreyer, and Christer Erse ´us* (SK) Department of Zoology, University of Gothenburg, Box 463, SE-405 30 Go ¨ teborg, Sweden; present address: Richard Gilder Graduate School, American Museum of Natural History, Central Park West @ 79th Street, New York, New York 10024, e-mail: skvist@amnh.org; (JD) Department of Biological Sciences, Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, VA 23062, U.S.A., e-mail: jcdrey@vims.edu; (CE) Department of Zoology, University of Gothenburg, Box 463, SE-405 30 Go ¨ teborg, Sweden, e-mail: christer.erseus@zool.gu.se Abstract.—Tubificoides blakei and T. methanicus, both new species of oligochaetes, are described from 2156 and 2170 m depth on the Blake Ridge Diapir, near the intersection of the Carolina Rise and the Blake Ridge, off the continental shelf of North and South Carolina (U.S.A. East Coast). Tubificoides blakei is characterized by the long, parallel teeth of its bifid crotchets, and its mushroom-shaped, cuticular penis sheaths. It appears most closely related to two other deep-water species reported from the northwest Atlantic Ocean, T. bruneli Erse ´us, 1989 and T. aculeatus (Cook, 1969) but differs from these in the detailed morphology of the penis sheaths. Tubificoides methanicus lacks hair chaetae but is recognized by its numerous bifid chaetae, which have long, somewhat diverging teeth, the upper teeth often being longer than the lower ones, and its smooth, funnel-shaped penis sheaths. It does not seem to be closely related to any other known deep-sea species of Tubificoides, but it resembles the littoral, holarctic, T. pseudogaster (Dahl, 1960), differing from the latter mainly by its greater number and larger size of the posterior chaetae. Tubificoides Lastockin, 1937 (subfamily Tubificinae) is a large, marine oligochaete taxon with about 50 described species worldwide (Milligan 1996), the most recent addition being T. calvescentis Erse ´us et al., 2005. The genus is morpho- logically confusing since most of the genital structures (e.g., male ducts, sper- mathecae) are rather similar throughout the species; therefore, nominal taxa are largely discriminated on the basis of unique combinations of minute differenc- es in the structure of the cuticle (some species are heavily papillated), the ap- pearance and arrangement of the chaetae, and the shape of the cuticular penis sheaths. In many cases, it is easy to identify a particular species as such, but it is difficult to see any clear lines of evolution in these morphological charac- ters (Milligan & Erse ´us pers. obs.); thus, the phylogenetic relationships within Tu- bificoides are largely unknown. A high number of specimens of Naidi- dae [formerly Tubificidae; see Erse ´us et al. (2008); see also International Com- mission of Zoological Nomenclature (2007)] were collected from two research cruises at the Blake Ridge methane seep at 2156 and 2170 m depth. They represent * Corresponding author. PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 121(4):531–540. 2008.