Climatius is an extinct genus of spiny shark

Acanthodii

Acanthodii is a class of extinct fishes, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans...

. Fossils have been found in both Europe and North America.

Climatius was an active swimmer judging from its powerful caudal fin and abundant stabilizing fins, and probably preyed on other fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s. Its lower jaw was lined with sharp teeth which were replaced when worn, but the upper jaw had no teeth. It also had large eyes, suggesting that it hunted by sight.

Although it was a small fish, at 7.5 centimetres (3 in), to discourage predators, Climatius sported a total of fifteen sharp spines. There was one spine each on the paired pelvic and pectoral fins, and on the aingle anal and two dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

s, and a further four pairs without fins on the fish's underside.