Vertebral Number in North American Sculpins of the Myoxocephalus quadricornis-Complex

X-rays of 438 North American specimens of the Myoxocephalus quadricornis-complex (Cottidae) showed mean vertebral counts (including urostyle) of 38.433 in the deepwater sculpin which inhabits inland continental lakes; 41.097 in the freshwater relict in lakes on Victoria Island, Northwest Territories; 41.417 in newly discovered freshwater relicts in Nauyuk, Stanwell-Fletcher, and Sophia lakes, Northwest Territories; and 41.821 in the coastal fourhorn sculpin living in brackish and marine coastal waters and certain adjacent fresh waters. Except for the Victoria and the three lake relicts, the vertebral means of all pairs of these groups differed at P <.01 or <.001. Of the coastal fourhorn sculpin and the deepwater sculpin 91% are identifiable using only vertebral number, of the Victoria relict and the deepwater sculpin 68%, and of the Victoria relict and the coastal fourhorn only 10%.Vertebral counts alone permit recognition of the deepwater sculpin as a subspecies, Myoxocephalus quadricornis thompsonii Girard, 1852, distinct from the arctic coastal fourhorn sculpin provisionally referred to M. q. hexacornis (Richardson, 1823) and suggest classification of the Victoria Island, Nauyuk, Stanwell–Fletcher, and Sophia lake relicts with the coastal form, rather than with the deepwater sculpin. Relicts in the latter three lakes are suggested to be postglacial in origin.