On the front of each dorsal fin there is a sharp spine attached to them, giving the spiny dogfish its name. The first spine is about half as long as the second spine. The pectoral fins form nearly perfect equilateral triangles, with rounded rear tips, and slightly concave rear margins. The pelvic fins are closer to the second dorsal fin than to the first dorsal fin. One the caudal fin, there is no notch on the upper lobe and the lower lobe is not well-developed. There is no anal fin on the Spiny dogfish.