Sabatieria challengerensis sp. n. (Figs 4–5, Table 1) Material examined. Holotype male (NIWA 865987), collected 5 June 2007, western Challenger Plateau (532 m water depth), 40.8814 °S, 170.8603 °E. Characteristics of surface sediment layer (0–5 mm): mostly silt/clay (67.6 %), with fine sand (15.1 %) and very fine sand (11.4 %); calcium carbonate content: 56.0%; total organic matter content: 2.1 %; chloroplastic pigment concentration: 1344 ng /gDW sediment. Three male and four female paratypes (NIWA 865988), same data as holotype. Etymology. This species is named after Challenger Plateau, the type locality. Description. Male Body cylindrical, tapering slightly towards anterior extremity. Cuticle with transverse rows of dots, lateral differentiation consisting of larger, irregularly-spaced dots. Two dorso- and two ventro-lateral rows of short, sparse somatic setae. Head set-off by depression at level of cephalic setae. Six inner labial papillae, six outer labial papillae, and four short cephalic setae. Anterior portion of buccal cavity cup-shaped, lightly cuticularised at base, posterior portion narrow. Fovea amphidialis spiral, 3.0 turns, located immediately posterior to cephalic setae. Marginal tubes arising from base of buccal cavity and extending to posterior end of pharynx. Pharynx gradually swelling towards posterior, not forming true bulb, cardia short, 5–10 µm long. Nerve ring near middle of pharynx. Secretory-excretory system present, cellular body of ventral gland at level of intestine, pore situated 0.5 –1.0 cbd posterior to nerve ring. Intestine wall with numerous small, colourless granules, with differentiation of rounded cells containing more densely packed granules in anterior portion. Reproductive system diorchic with outstretched testes. Anterior testis on left of intestine, posterior testis on right of intestine; one specimen with opposite arrangement. Mature sperm cells globular, nucleated. Spicules paired, equal, arcuate, 1.3–1.8 abd long, without capitulum, and with central cuticularised ...