Aptocyclus ventricosus (Pallas, 1769) .

Smooth Lumpsucker. To 45 cm (17.7 in) TL (Solomatov and Orlov 2018). Japan and Okhotsk Seas to Providence Bay, Gulf of Anadyr; northern Bering Sea, Alaska to North Pacific Ocean south of Aleutian Islands and Gulf of Alaska to Mathieson Channel, British Columbia (Mecklenburg et al. 2002). Pelagic; depth: usually found in deep waters from near surface to at least 940 m (3,083 ft) (Solomatov and Orlov 2018). Also taken in a bottom trawl towed at 1,556 m (5,104 ft) (Hoff and Britt 2003), but the fish may have entered the net above the bottom; also listed to depth of 1,700 m (5,576 ft) in Federov et al. (2003). Kido and Shinohara (1996) showed that the species named Pelagocyclus vitiazi Lindberg & Legeza, 1955 is the juvenile stage of A. ventricosus . Genetic data recently presented by Okazaki et al. (2020) indicates that this species may consist of distinct eastern and western populations.