Erimacrus isenbeckii is a species of marine crab in the family Cheiragonidae, commonly known as the horsehair crab or kegani in Japan. It is native to the cold temperate waters of the North Pacific Ocean, particularly around northern Japan, the Sea of Okhotsk, the Bering Sea, the Kamchatka Peninsula, Alaska, and parts of the Russian Far East. The genus name Erimacrus derives from Greek roots eri- meaning “very” or “much” and makros meaning “long” or “large,” referring to its appendages, while the species epithet isenbeckii honors the German naturalist Heinrich von Isebeck. This crab inhabits sandy and muddy seabeds at varying depths and has long been an important commercial species in Japanese and North Pacific fisheries.

Horsehair crabs are highly valued for its sweet, firm meat and rich tomalley, especially in Hokkaidō, where it is considered a regional specialty. As a food source, Erimacrus isenbeckii provides crab meat from its legs, claws, and body, as well as kani miso (the hepatopancreas), which is consumed for its intense umami flavor. It is typically boiled in salted water to preserve its natural sweetness, then served chilled, incorporated into rice bowls, soups, hot pots, or used in sushi and sashimi preparations. In northern Japanese cuisine, particularly in Hokkaidō, it is closely associated with winter seafood traditions, and it is also consumed in Russian Far Eastern and Alaskan coastal foodways. Processed forms include picked crab meat, canned crab, and crab-based seasonings or pastes.

Nutritionally, Erimacrus isenbeckii contains eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), astaxanthin, taurine, and free amino acids such as glycine and glutamic acid that contribute to sweetness and umami perception. It also contains chitin in its exoskeleton.