p of their heads. Sharp spines are typically present on the preopercles. In M. octodecimspinosus, this spine is prominent (Herald, Living Fishes of the World 248-249).
Members of the family Cottidae have two dorsal fins. The first dorsal fin is short-based, whereas the second is long-based. The two fins may be either slightly separate or united. The fishes' caudal fin may be either broad, rounded, or truncate. Moreover, their pelvic fin is small and thoracic. Finally, the cottid pectoral fins are large, fan-shaped, and lateral on the body (Herald, Fishes of North America 227-230).
Sculpin color is rather variable. The body may be blotched, scrawled, mottled, or spotted. It may also be slightly iridescent. The fish can change color to blend in with their surroundings ("Salty" 67). Hence, this "motley" group may match the shade of the substrate (Jenkins & Burkhead 625).
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