Evolution and systematics

The Scorpaeniformes, the mail-cheeked fishes, are united by the presence of a bony ridge called a "suborbital stay" on the cheek, running horizontally below the eye and providing an armored look to the head of most species. The suborbital stay is a posterior extension of the second infraorbital (eye socket) bone. In the sculpins (Cottoidei), this suborbital stay tends to be very prominent, while in the greenlings (Hexa-grammoidei) it is not easily seen.

The ancestral scorpaeniform stock is considered to have derived from a generalized percoid (perch) fish. That is to say, cottoid (sculpin) and hexagrammoid (greenling) fishes are among the most recently evolved, advanced fishes. The Scor-paeniformes is the fourth largest order of fishes, including about 29 families, about 260 genera, and 1,400 species. Most of these fishes are bottom-dwelling or live near the seabed. Nine families are covered in this chapter, with the remainder covered in Scorpaeniformes I and II.

Among the scorpaeniform fishes, the suborder Cottoidei includes between seven and 13 families in modern classifications. Historically, various additional cottoid families have been distinguished, often containing only one species. The most prominent families include the sculpins (Cottidae, with 305 species in 70 genera), fathead sculpins (Psychrolutidae, with 11 species, five genera), poachers (Agonidae, with 49 species, 20 genera), lumpfishes (Cyclopteridae, with 27 species, eight genera), and snailfishes (Liparididae, with 195 species, 13 genera). Also within the Cottoidei are two families of Lake Baikal fishes, the Cottocomephoridae (Baikal sculpins, with 24 species, eight genera), and Comephoridae (Baikal oilfishes, with two species, one genus). The Baikal oilfishes are distinguished by being the only viviparous (live-bearing) cottoid fishes. A monotypic (one species) family, the Normanichthyidae, consists of one marine species off Chile that is often included within the Cottoidei. That species, Normanichthys crockery, would be the only cottoid fish having a swim bladder, but the anatomical description by Yabe and Uyeno (1996) concludes that the family is of uncertain systematic position within the Scorpaeniformes, and not correctly within the Cottoidei. Other families common in various classifications include the Cottunculidae (here included within the Psychrolutidae), the Icelidae (sometimes distinguished from Ereuniidae, both within the Cottidae here), and the Hemitripteridae (here included within the Cottidae). The species in the Psychrolutidae are usually included within the Cottidae in older works, but Jackson and Nelson (1998) have described the unique features of sensory canals and associated bones on the head which, together with other characters, distinguish the fathead sculpins from the other sculpin species. Some classifications place the liparidid fishes within the Cyclopteridae. Cottoid fishes probably first appeared in the North Pacific and only invaded the Arctic and North Atlantic Oceans 3.5 million years ago.

The zoogeography of cottoid fishes centers on the Pacific coast of North America. The other scorpaeniform suborder considered within this chapter is the Hexagrammoidei, the greenlings, which includes the largest family of fishes endemic to the North Pacific, the Hexagrammidae (11 species, five genera). Some classifications separate the combfishes into a separate family, the Zaniolepidae. Another family usually included within the Hexagrammoidei is the Anoplopomatidae, which includes the sablefish (Anoplopoma fimbria) and the skil-fish (Erilepis zonifer). Sometimes the skilfish is separated into the monotypic family Erilepidae, also with these two families separated from other hexagrammoids into the Anoplopoma-toidei.

A tidepool sculpin (Oligocottus maculosus) in the Pacific Ocean, near the United States. Each sculpin changes color to match its tidepool, or buries itself in sand. If it is washed out of its tidepool, it uses its sense of smell and returns to its own pool. (Photo by Nancy Sefton/Photo Researchers, Inc. Reproduced by permission.)

A tidepool sculpin (Oligocottus maculosus) in the Pacific Ocean, near the United States. Each sculpin changes color to match its tidepool, or buries itself in sand. If it is washed out of its tidepool, it uses its sense of smell and returns to its own pool. (Photo by Nancy Sefton/Photo Researchers, Inc. Reproduced by permission.)

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