Japanese spider crab

Description

The Japanese spider crab (Macrocheira kaempferi) is a species of marine crab that lives in the waters around Japan. It has the largest leg-span of any arthropod. It goes through three main larval stages along with a prezoeal stage to grow to its great size. The genus Macrocheira contains multiple species. Two fossil species of this genus have been found, M. ginzanensis and M. yabei, both from the Miocene of Japan. Its diverse taxonomic history is an important part of what these creatures are and how they evolved to be what they are today. They are sought by crab fisheries, and are considered a delicacy in Japan. Conservation efforts aim to protect these creatures and their population from overfishing. The Japanese spider crab is similar in appearance to the much smaller European spider crab (Maja squinado). The Japanese spider crab has the greatest leg span of any arthropod, reaching up to 3.7 m (12.1 ft) from claw to claw. The body may grow to 40 cm (16 in) in carapace width and the whole crab can weigh up to 19 kg (42 lb) second in mass only to the American lobster among all living arthropod species. The males have the longer chelipeds; females have much shorter chelipeds, which are shorter than the following pair of legs. Apart from its outstanding size, the Japanese spider crab differs from other crabs in a number of ways. The first pleopods of males are unusually twisted, and the larvae appear primitive. The crab is orange with white spots along the legs. It is reported to have a gentle disposition despite its ferocious appearance. The Japanese name for this species is taka-ashi-gani, literally translating to “tall legs crab.” It also has a unique molting behavior that occurs for about 100 minutes, in which the crab loses its mobility and starts molting its carapace rear and ends with molting its walking legs. Its armored exoskeleton helps protect it from larger predators such as octopuses, but also uses camouflage. The crab's bumpy carapace blends into the rocky ocean floor. To further the deception, a spider crab adorns its shell with sponges and other animals. The way in which a spider crab is able to pick up and cover itself with such organisms is by following a specific routine behavior. Upon picking up the object with the crab's slender chelipeds, the chelae are used to twist and tear off the organism, such as a worm tube or sponge, from the substrate on which it currently resides.