The Japanese spider crab is the largest living arthropod. It is a particularly ancient species of crab, considered a living fossil. It is the only living species of the genus Macrocheira; other species of the genus have only been described as fossils.
It lives in the depths of the Pacific Ocean near Japan. It has an average life of about 100 years. The Japanese giant crab is caught using small bottom trawls and is eaten after salting and stewing it. It is found at Sagami Bay, Suruga and Tosa and also around the Izu Islands.
Hunting for this crab is prohibited during the spring when it releases its eggs. It is considered a specialty around Suruga Bay, but crab numbers have declined in recent years, and efforts are underway for its protection. In Wakayama Prefecture, crabs are caught when they move into shallower waters in spring.
These crabs are also used for research and ornamental purposes. They have a mild nature and are often kept in aquariums. Populations of this species of crab have diminished over recent years and many efforts are being made to protect them.
One of the primary methods of recovery of the species being used is restocking artificially cultured juvenile crabs in fisheries. Additionally, laws have been put into place in Japan that prohibit fishermen from harvesting spider crabs from January through April, during their typical mating season when they are in shallower waters and more vulnerable to being caught.
This protection method seeks to keep natural populations growing, and enables time for juvenile spider crabs to go through the early stages of their lifecycle.
The Japanese spider crab needs protection
M. kaempferi is widespread in the Pacific area surrounding the archipelago of Japan.
It prefers sandy bottoms at depths of 150 - 800 m, more frequently between 200 and 300 m. In spring it spawns on shallower bottoms (50 m). In maturity it can reach a leg span of up to 4 m, with a body size of up to 37 cm and a weight of up to 20 kg.
The crab has an orange colored body, but has white dots on its thin legs. The claws of male specimens become longer than its legs; when open these can stretch for 3 meters. The width of the shell, oval and rounded, can reach 30 cm and reach a length of 40 cm.
Its composite eyes are located on the front, and two quills (thorns) protrude between them. Younger specimens have hairs and spines on their shells, and their frontal spines are longer, but these gradually atrophy as they get older.