The "killer crab" is bigger than the king crab! Is it delicious?

Legend has it that many Japanese fishermen and tourists were attacked in the sea where killer crabs appeared. It can clamp people's arms with its huge claws, and hold its prey tightly with its remaining legs, and slowly drag it into the deep sea. It is said that dozens of people have been buried in the crab's belly. The protagonist of this legend, the "killer crab", is the giant claw crab.

The giant crab is the largest known arthropod in existence. It is named after the huge first pair of legs (chelipeds) of the male. The largest individual of this species that has been discovered weighs 19 kilograms, and its chelipeds on both sides are 3.8 meters long, equivalent to the length of a small car . Will the giant crab really "kill" humans? Is it really that powerful?

A male giant crab specimen collected by the Shanghai Natural History Museum (original material from the Internet)

Who is Gan?

The Latin scientific name of the giant crab, Macrocheira kaempferi, was named by Dutch zoologist Coenraad Jacob Temminck in 1836. He used the specific epithet kaempferi (translated as "Gan" in Chinese) to commemorate Engelbert Kaempfer , a German doctor and naturalist who once lived in Japan.

Kampfer traveled to many Asian countries and was the first European to make a natural history description of Asia, especially Japan. This large crab was recorded in his book "Wonders of the Kingdom".

Brutal killer crab?!

Do you feel the pressure of the giant crab? Image source: animalworld.com.ua

The specimen above restores the standing posture of the giant crab when it was alive. Looking at its huge body and spider-like shape, are you scared? Does it immediately awaken the fear of giants and spiders deeply rooted in your genes? No wonder the rumor of "killer crab" is so popular.

If you look closely at its legs, you will find that this guy is just a "big fool on stilts". The huge body makes the small claws on the claws look even smaller. Not to mention that the claws are as slender as the legs, and there is not much crab meat, no, muscle.

Therefore, the legend of the killer crab is completely a rumor . However, there is no smoke without fire. These rumors actually stem from the real habit of the giant crab - it eats carrion . The giant crab moves slowly and cannot swim. It usually lives a Buddhist life on the seabed where there is a lot of land and little "seafood". It is willing to eat animal carcasses, residues, and passing shellfish that fall from the sea. The main feature is that it is not a person who likes to work hard and is not picky about food.

Adult giant crabs are huge and hard to rival, so they can be "Buddhist", but young giant crabs live a "hard-working" life.

Like other crabs, the cephalothorax and legs of giant claw crabs gradually grow larger and longer during molting. The juvenile characteristics also fade away. For example, the protrusions on the carapace gradually become fewer and rounder from dense and sharp. The once dense hooked bristles on the carapace gradually become fewer and eventually disappear. Even the male's iconic large claws are significantly elongated after adulthood.

Giant crab in the "youngster" stage Source: Reference 1

But how can the hooked bristles and protuberances on the carapace help?

Juvenile giant crabs, like the bottom-dwelling spider crabs, use camouflage strategies to protect themselves. They decorate their backs with sponges, corals, or other debris. The hooked bristles and sharp protrusions on the carapace become the attachment points for these decorations . The bristles of adult individuals have been reduced and disappeared, and even if they remain, they are no longer hooked, and cannot and do not need to attach decorations. Of course, "marine nail households" such as barnacles, hydras, and algae will "pamper" every moving object in the sea equally.

Spider crabs decorate themselves with corals. Source: BBC "Blue Planet II"

The giant claws that only start to grow after the male reaches adulthood will obviously come in handy when they are "holding a pair".

Male giant crab: I just wanted to find a partner, but I accidentally became the best in the world (smug face)

Image source: Shanghai Natural History Museum official website

Lonely Cancer

Although the giant crab is known as the "world's best" and a real traffic star, taxonomists have only recently figured out its evolutionary position. This is certainly not the fault of taxonomists' negligence, but mainly because the giant crab has no strong single morphological features that can distinguish it from other similar species, which really makes taxonomists feel overwhelmed.

From the beginning, taxonomists classified it into the family of spider crabs based on its similar morphology to spider crabs. But this family itself is a mess, with highly similarities among them. There were 12 subfamilies, and it belonged to the subfamily of Macrochelys. Later, the family of spider crabs was upgraded to a superfamily, but the subfamily of Macrochelys did not follow the upgrade. Instead, it was demoted and integrated into the family of Acrocephala (formerly the subfamily of Acrocephala). This result is still not convincing.

It was not until 2022 that a research team composed of four natural history museums and universities in France, Australia, Hong Kong, China, and Singapore, combined various morphological and mitochondrial DNA genetic evidence to propose that the genus Macrochelys is a monophyletic group, which is highly divergent from other similar species such as the Acrocephalidae, and that the Macrochelydae family should be established.

Although it has successfully upgraded and finally established its own family, the Macrochelydae family can be said to be a "downtrodden family". There is only one existing species in this family, the Macrochelydae gangrensis . The rest are extinct fossil species, of which about 5 species have been discovered. Its "brothers and sisters" lived in the northeastern Pacific Ocean in today's United States and Canada from the Eocene to the Miocene of the Cenozoic Era. Although the remaining fossil individuals are much smaller than the Macrochelydae gangrensis, morphological evidence supports that they belong to the same genus/family of Macrochelydae. Today, only one species of the Macrochelydae gangrensis is left, living alone in a corner.

Can’t tell the difference between giant crab and king crab?

In addition to the giant crab, it is also called high-legged crab, high-foot crab, Japanese spider crab, killer crab and king crab...

Is the giant claw crab a king crab? Of course not!

Although the king crab is large, its largest weight and length are about half of those of the giant claw crab. In addition, the king crab, namely the Kamchatka stone crab Paralithodes camtschaticus and the giant claw crab M. kaempferi , actually belong to different groups, but they are similar in shape.

The difference between giant crab and king crab:

(1) Different shell colors. Giant claw crabs are naturally orange-red with white markings. King crabs are reddish brown or purple-red when alive, and turn orange-red when cooked.

(2) The shape of the crab shell is different. The crab shell is also called the cephalothorax. The shell of the giant claw crab is pear-shaped, narrow and long. The shell of the king crab is shaped like a navel orange and is short and fat.

(3) The shape of the legs is different. The legs of giant claw crabs are round and slender. The legs of king crabs are flat, wide and short (relatively speaking).

(4) The number of legs is different. The number of legs is the most obvious and stable difference. Usually the first pair of legs are chelicerae, which are used for feeding and holding the body; the back pair are walking legs, which are used for walking or swimming.

Giant claw crabs belong to the order Brachyura, which is what we often call crabs. Their abdomens are degenerate and folded back to the back of the cephalothorax. Hairy crabs, swimming crabs, fiddler crabs, Sesarma crabs, blue crabs, spider crabs, etc. all belong to this category, and generally have one pair of chelicerae and four pairs of walking legs .

The king crab belongs to the order Anisoura (also called Anisoura), which also includes the hermit crabs and armored shrimps we often talk about. The abdomen of this group is mostly soft and asymmetrical. Moreover, the last pair of walking legs of the king crab has degenerated and atrophied, and it looks like there is only one pair of chelicerae and three pairs of walking legs. And the chelicerae are one large and one small .

King crabs and hermit crabs have fewer legs and asymmetrical abdomens. Source: Internet

Giant claw crab: Which is more beautiful, me or the king crab?

Although the giant crab is known as the largest crab, it seems to be unknown in the food world. Is it true that the giant crab cannot be eaten?

Giant crabs are commonly called stilt crabs in Japan and are an important commercial fishing species in Japan. They are usually caught in large quantities by small trawlers in deep coastal bays at a depth of 200 to 300 meters. Toda Port in Akitsu City, Shizuoka Prefecture, located on the Izu Peninsula, is a large deep-water fishing port famous for its deep-sea aquatic products, and stilt crabs are also a local specialty.

Yes, it is edible! It is quite delicious! It can be steamed or grilled. It is said that the crab meat is very fresh and sweet, with a lot of crab roe and crab paste. However, it is difficult for it to survive after going out to sea, and it can only be frozen for long-distance transportation, which greatly reduces the taste. If you have the chance, you should try it nearby.

Local food store launches real crab meat frozen product

In addition to being used as food, a small amount is also used for display in aquariums, and there are even interactive activities where people can touch the giant crab live, which shows how gentle it is. (Portugal: It's useless to grow so big, but it's not as fierce as me) The huge crab shell can also be used for artistic decoration and specimen making.

There is a local custom of using the shells of tall crabs to draw ghost faces to ward off evil spirits. Source: Taelog

References

[1] Guinot Danièle, Davie PJF, Ming TL, et al. Formal re-establishment of Macrocheiridae Dana, 1851 (Decapoda: Brachyura: Majoidea) for the giant spider crab Macrocheira kaempferi (Temminck, 1836) based on a reappraisal of morphological and genetic characters[J]. Journal of Crustacean Biology, 2022(2):2.DOI:10.1093/jcbiol/ruac022.[2] International Biological Flora: Ginkgo biloba[J].Journal of Ecology, 2022.DOI:10.1111/1365-2745.13856.[3] Crane,P,R,et al.Ginkgo biloba: connections with people and art across a thousand years.[J].Curtis's Botanical Magazine, 2013, 30(Pt.3):239-250.[4] https://new.qq.com/rain/a/20200707A03NWR00 Japanese "killer crab" attacks fishermen, killing 60 people? How did the biggest shell delicacy become a terrifying creature?

Planning and production

Source: Shanghai Natural History Museum (ID: snhm01)

Author: Arisaema Shanghai Natural History Museum Exhibition and Education Center

Editor: Wang Mengru

Proofread by Xu Lailinlin