Japanese Spider Crab Facts | Anatomy, Diet, Behavior Habitat

The Japanese spider crab (Macrocheira kaempferi) is the largest of all crustaceans. It occurs on muddy or sandy bottoms in water to a depth of 30 – 50 m (100 – 160 ft). The crab is thought to feed on echinoderms, molluscs, crustaceans, and worms. It is also known as takaashigani means ‘tall leg’.

Japanese Spider Crab Facts

Anatomy

  • The length of the Japanese spider crab averages 25 × 30 cm (10 × 12 inches). Some spiders reach a length of 45 cm (18 inches).
  • Adult crabs are 4 m long. They weigh up to 16 – 20 grams.
  • Females have smaller abdomen than that of males.
  • They are admired for their long spindly legs which measure 2.4 – 2.7 m (8 – 9 ft) in length. Their legs are quite weak.
  • There are white spots on its orange legs.
Giant Japanese Spider Crab © www.tnaqua.org
Giant Japanese Spider Crabs © www.tnaqua.org

Distribution

  • Japanese spider crabs are distributed throughout the Pacific parts of the Japanese islands, Honshu including Sagami, Suruga, Tokyo Bay and Kagoshima Prefecture.
  • Some of the isolated population also occurs in Taiwan.
  • They are found to a depth of 50 – 600 m (16 – 1,970 ft).

Habitat

  • These spider crabs breed in the temperate waters including saltwater or marine habitats.
  • They make habitats at depths of 150–300 metres (490–980 ft).
  • Japanese crab spider are thought to occur in the deeper parts of the ocean.

Feeding Ecology & Diet

  • Japanese crab spiders are omnivores as they feed on both animals and plants.
  • Sometimes they also act as a scavenger to eat dead animals. Spider crabs supplement their diet with the shells of mollusks.
  • The diet includes fish, carrion, aquatic crustaceans, other marine invertebrates. Plant matter consists of algae and macroalgae.

Behavior

  • The Japanese spider crab uses it claws to run off potential predators but it cannot move swiftly.
  • Spider crabs are not thought to communicate with each other.
  • The sensory system of Japanese spider crab is not acute for the animal is not an active hunter nor does it possess natural predators.

Reproductive Biology

  • Spider crabs go through three stages; one megalopa stage and two zoeal stages. The zoeal stage averages 12 – 37 days while the megalopa stage lasts one month.
  • It takes 54 – 72 days to develop the planktonic larvae.
  • Young crabs are known to survive in shallow waters with warm temperatures.
  • Reports suggest that the Japanese spider crabs have a lifespan of 100 years in the wild.
  • Each season the female crab will lay 1,500,000 eggs but only a few are able to survive. These eggs measure 0.63 – 0.85 mm in diameter.
  • The eggs are hatched in 10 days.
  • They mate only once a year and the mating season ranges from January to April.
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