Slim, elongate, cylindrical body that tapers to a truncate tail with a concave margin. Robust and bony head with a wide mouth. Deeply notched dorsal fin with a singular dark spot on the first dorsal with thin white stripes located underneath. Faint thin white stripes run along the entire length of the second dorsal. The Northern Searobin has wide fan-like pectoral fins with 2-3 dark bars running across the fins. Appears to have "legs" which act as feelers, but they are the first three rays of modified pectoral fins. The upper body may appear brown/tan, brownish-red, or olive-green with mottling with about 5-6 white spots along the back. It has a flat white underbelly, and the tips of anal fin are white. The Northern Searobin typically reaches up to 10 inches in length with larger specimens reaching up to 15 inches.