Japanese spider crab

Japanese spider crab

Japanese spider crabs might look like creatures from a science fiction movie, but these massive arthropods are surprisingly gentle. Among the 60,000 species of crustaceans on Earth, they hold the title of largest, with their leg span reaching up to an impressive 12.5 feet from claw to claw. They are also among the largest arthropods, a group of animals characterized by their external skeletons, jointed legs, and lack of backbones. The spider crab’s defining feature is its 10 long legs, which give it its arachnid-like appearance.

Habitat and Appearance

These crabs inhabit the Pacific waters near Japan, extending as far south as Taiwan. They dwell at depths ranging from 164 to 1,640 feet, favoring cooler temperatures around 50°F. During their reproductive season, they migrate to shallower waters.

Their mottled orange-and-white bodies, creamy undersides, and spiny, oval-shaped carapaces help them blend in with the rocky ocean floor. Males tend to be larger than females, with longer claw-bearing legs, while females have broader abdomens to carry their eggs.

Diet and Behavior

Despite their formidable appearance, Japanese spider crabs are scavengers rather than hunters. They feed on dead animal and plant matter but occasionally consume live fish or smaller crustaceans.

Juveniles often camouflage themselves by adorning their shells with sponges or anemones, a behavior common among decorator crabs. However, adults rarely bother with such decorations since they face few predators at the depths where they live.

Reproduction

During mating season, from January to April, these crabs move to shallower waters. Mating involves the male transferring a sperm packet to the female as their abdomens press together. Females carry the fertilized eggs, tiny at just 0.03 inches, under their abdomen. Each female can produce over a million eggs, though only a small fraction survive to hatch.

Eggs hatch after about 10 days, with no parental care provided. The young crabs molt for the first time within nine to 12 days of hatching. Observations in captivity have recorded a single molt lasting 103 minutes, with the crab growing by nearly 22% afterward.

Conservation

Japanese spider crabs have not been formally assessed by the International Union for Conservation of Nature (IUCN), but their numbers have declined in recent years. They are not heavily targeted by commercial fisheries due to their deep-water habitats, though they are occasionally caught in small trawl nets. Considered a delicacy in Japan, their fishing is strictly regulated during the breeding season to help protect their population.

Despite their immense size and alien-like appearance, Japanese spider crabs remain a fascinating example of the ocean’s biodiversity and the delicate balance required to preserve these unique species.

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