Spider Crab

Any kind of spider crab in the decapod family Majidae (or Maiidae; class Crustacea). Spider crabs, which have large, spherical bodies and long, spindly legs, move slowly and sluggishly. The majority are scavengers, particularly of dead meat.

Majids are a globally distributed marine group that is commercially fished in temperate areas like the North Pacific. The long-beaked spider crab (Macropodia rostrata) of European coastal waters, for example, has a body diameter of around 1 cm (less than 0.5 inches). The gigantic crab (q.v.) of the Pacific seas near Japan is the biggest spider crab and possibly the largest known arthropod. This crab's (Macrocheira kaempferi) extended claws measure more than 4 m (13 ft) from tip to tip.

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The spider crab's head is beak-shaped, and the body is covered in hairs, spines, and tubercles (knobby projections) that are commonly tangled with algae, sponges, and other creatures. A large portion of this material is adhered to the crabs by a mucus-like secretion from the mouth.

The kelp crab (Pugettia producta), a spider crab found amid seaweed throughout the Pacific coast from Canada to Mexico, is around 1.25 cm (0.5 inches) broad and 2.5 cm (1 inch) long. On top, it's green and red, and on the bottom, it's green.

Parthenope investigatoris, an Indian Ocean spider crab, is disguised to mimic the coral on which it dwells.

Spider crabs of the species Libinia, Hyas, Sternorhynchus, Pitho, and Lambrus are widespread throughout North America's Atlantic coast. Loxorhynchus, Pugettia, and Epialtus are three genera of Pacific coast spider crabs.

In this article, we are going to discuss giant spider crab, spider crab legs, Japanese spider crab adaptations, and common spider crab.

Body Design of Japanese Spider Crab

The Japanese Spider crab has white markings on its legs but an orange body. Their body length is 37 centimetres (15 inches). They may reach a weight of up to 20 kilos (44 pounds). Their legs may stretch up to 4 metres in length (13 feet). Males have chelipeds that are rather lengthy. The chelipeds of females are considerably shorter than those of men. Even if it loses three of its walking legs, the Japanese spider crab can live. If it loses a leg, it has the potential to regrow a leg during moulting.

Their protective exoskeletons shield them from bigger predators.

To avoid predators, the Japanese Spider crab uses its rough carapace to blend in with the ocean floor.

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It also has an unusual technique of camouflaging itself from predators. Unlike other crabs, which have numerous species and types of creatures on their carapace, the Japanese spider crab only has sponges on its carapace because it has so few predators to hide from. It transports the sponge(s) to various locations, and the sponge may feed it with floating food.

What is a Japanese Spider Crab?

Japanese spider crabs may resemble creatures from a 1950s science fiction film, yet they are gentle giants.

They are, indeed, colossal. Japanese spider crabs are the biggest of the 60,000 crustaceans on the planet, reaching lengths of up to 12.5 feet from the tip of one front claw to the other. They are also one of the world's biggest arthropods, which are animals that lack a backbone, have external skeletons, and have multiple-jointed limbs. In the case of this crab, the appendages are its ten legs.

Geographic Range and Appearance

Japanese spider crabs may be found on the Pacific side of Japan as far south as Taiwan, at depths ranging from 164 feet to 1,640 feet. (They spawn at the shallower end of that range.) They flourish at temperatures about 50 degrees Fahrenheit.

Their mottled orange-and-white bodies, cream-coloured undersides, and spiky, oval carapaces mix in with the rocks on the ocean floor in these waters. Giant Japanese spider crabs have arachnid-like shells and lengthy legs, thus its popular name. Spines are also found behind and in front of these creatures' short eyestalks.

Males are larger and have larger chelipeds, or claw-holding legs, than females, who have broader abdomens to carry their eggs.

Diet and Behaviour

These slow-moving crabs prefer to scavenge for dead animal or plant materials rather than hunt, although they will eat live fish or invertebrates like other crustaceans.

This species belongs to a group of crabs known as decorator crabs, which use sponges or anemones to decorate their shells for concealment. Juvenile Japanese spider crabs will do this, but because there are few predators in the depths where they reside, adults do not need to dress to impress.

Japanese Spider Crab Life Cycle

The mating season for the Japanese Spider Crab occurs in the early months of spring, from January to March. Despite the fact that its early stages of life have been thoroughly recorded, nothing is known about its mating behaviour. Internal fertilisation occurs in them. Male crabs deposit their sperm, which is kept in spermatophores, into female crabs using their first two chelipeds. During a mating season, a female may lay up to 1.5 million eggs, although only a small percentage of the eggs hatch. The eggs are around 0.63-0.85 millimetres in diameter. Females keep their eggs on their abdomen until they hatch.

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They do this in order for the mother to oxygenate the eggs by moving the water around them. When the eggs hatch, they're left to fend for themselves. The hatching of the eggs takes around 10 days.

The larval stage of the Japanese Spider crab consists of three stages.

The first two stages are zoeal, while the third is a megalopa stage.

The optimal temperature for the larval stages is 15-18 degrees Celsius. The zoeal phases last between 12 and 37 days. The megalopa stage lasts around 30 days. Only 75% survive the first zoeal stage, with only 33% surviving the second zoeal stage and the megalopa stage.

The larval stages of Japanese Spider crabs are located in shallower waters than adult Japanese Spider crabs. The Japanese Spider crab may live for up to 100 years in its native habitat.

Reproductive Behaviour

During mating season, which lasts from January to April, Japanese spider crabs move to the shallower end of their depth range. Internal fertilisation occurs when the male inserts a spermatophore, or sperm packet, into the female as their abdomens push together. The female's abdomen, sometimes known as the apron, is where the fertilised eggs are carried.

Giant Japanese spider crabs are huge creatures that start off tiny — females lay over a million eggs that are about.03 inches long. Few will survive to hatch, but those who do will emerge after approximately 10 days with no parental care. They moult for the first time around nine to twelve days after hatching.

A moult of a single Giant Japanese spider crab in captivity took 103 minutes, and the crab's growth rate was approximately 22 percent, according to researchers.

Where Do Japanese Spider Crabs Live?

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The Japanese Spider crab is primarily found on the Japanese islands' pacific coast. They are primarily found in the bays of Sagami, Suruga, and Tosa, as well as off the coast of the Kii peninsula.

They often occupy the sandy and rocky slope of the ocean near the land at an average depth of about 200 metres and live at a depth of approximately 50-600 metres (164 to 1968 feet) (656 ft).

Conservation

The International Union for Conservation of Nature has not reviewed giant Japanese spider crabs, although the species' harvest has fallen in recent decades. Because they reside at such depths, they are not vulnerable to large-scale commercial fishing. 

However, when they are fished, they are captured in tiny trawl nets. They are considered a delicacy in Japan, however, fishing for them is forbidden during their mating season to allow their population to grow.

Japanese Spider Crab Adaptations

Although their protective exoskeletons protect them from bigger predators like octopuses, gigantic spider crabs also utilise camouflage. The rough carapace of the crab fits nicely with the rocky ocean floor. A spider crab would cover its shell with sponges and other creatures to enhance the illusion.

Giant Spider Crab Facts

1. They Like Cold Water

It is unknown the temperature the Japanese Spider Crab likes. When the mating season begins, they don't appear to mind the warm water.

It is widely assumed, however, that they prefer a temperature of approximately 10 °C (50 °F) since they remain at a depth of roughly 300 metres (980 ft). Despite the fact that they can withstand temperatures ranging from 6 to 16 °C (43 to 61 °F), they are generally kept in aquariums at this range.

2. They are Scavengers Pur Sang

When you look at a Japanese Spider Crab, you can't help but believe it's clumsy. These lengthy legs certainly don't help them when it comes to looking for prey.

Their favourite pastime is scouring the ocean floor for the carcasses of recently killed creatures and picking them apart with their long legs.

3. The Crab Is in Fact an Omnivore

The fact that they like feasting on the dead carcasses of other marine animals does not imply that they only consume flesh.

They also utilise their long legs to collect plants and algae from the ocean floor. So, when it comes to food, the Japanese Spider Crab isn't choosy at all!

4. Japanese Spider Crabs Get Very Old

Because Japanese Spider Crabs may live to be as ancient as humans, their food must be highly nutritious.

Even better, if they are not killed by a predator like an octopus and die naturally, their odds of living for more than a century are significantly higher than ours!

5. They are Considered a Delicacy

Crabmeat is delicious, it's a well-known truth. Is the situation any different for Japanese Spider Crabs? No, in many regions of Japan, they are regarded as a real delicacy!

The issue is that overfishing has severely reduced their number, and precautions have been made to prevent the species from becoming extinct. One of them is that hunting for these crabs is forbidden in the spring when they migrate to shallower waters to mate.