Japanese Spider Crabs

The Japanese spider crab (Macrocheira kaempferi) is the largest living arthropod. Fully grown, it can reach a leg span of almost 4 metres (13 feet), a body size of up to 37 centimetres (15 inches) and a weight of up to 20 kilograms (44 pounds). The Japanese spider crab has an orange body, but it has white spots on its thin legs.

The claws of male specimens become longer than its legs and a large males claws, when opened, can widen to 3 metres. The width of the oval-shaped and vertically rounded shell can reach up to 30 centimetres and can be up to 40 centimetres in length.

The Japanese spider crabs compound eyes are situated on the front and two thorns stick out between them. Younger specimens feature hair and thorns on the shell and their frontal horns are longer, however, these gradually waste away as they grow older.

Japanese Spider Crab Habitat

The Japanese spider crabs natural habitat is on the bottom of the Pacific Ocean (some 300 – 400 metres deep) around the Japanese archipelago, where it feeds on dead animals and shellfish. Japanese spider crabs often live in the seabed at depths of 150 – 800 metres, however, they are found most prominently in depths of 200 – 300 metres. In spring, they can often be found laying eggs in waters as shallow as 50 metres.

Japanese Spider Crab Reproduction

Mating takes place with the ventral surfaces of the crabs opposing each other and occurs as soon as the female completes her molt. Fertilization is internal. The females abdomen is wider than the males, as in most crabs, to provide space for the brooding egg mass. Eggs are generally laid shortly after mating.

The Japanese spider crab is believed to have a life expectancy of up to 100 years. It is a particularly old species of crab and it is often referred to as a living fossil.