Macrocheira Kaempferi

Macro refers to large, while cheira refers to the frontal appendages of arthropods (typically large pincer claws); Kaempferi refers to a specific family of crab (as far as I can recall anyway). Together, this makes the scientific name for the Japanese spider crab.

Macrocheira by itself indicates the crab’s genus, or classification of closely related species. This is separate from the species macrocheira kaempferi because although some arthropods may be of the same genus, they are not able to interbreed successfully unless they are the same species.

Indeed, the Japanese spider crab, and all other crabs, are arthropods. What is an arthropod? An arthropod is a creature with a shell of chitin that sheds periodically, has the body of an invertebrate, and is recognizable by its segmented joints and body. This category also includes centipedes, spiders, lobsters, and similar. Crustaceans and arachnids.

Right, the Japanese spider crab (called taka-ashi-gani(タカアシガニ) in Japanese) is also massive in adulthood, I’ve neglected to say. On average, it will grow around 3 meters in length, which is nearly the length of two Cheshirs stacked on top of each other (I am a human). That’s pretty good for the crab, I think it’s the biggest living crab in the world, even.

During the process of conception, the male will insert its spermatophores into the female’s abdomen using its front claws, a very classy form of reproduction. The actual fertilization process of the egg is internal, but once fertilized, the female will carry the eggs upon its back and lower abdomen during incubation in order to oxygenate the eggs with its legs. There may be millions of eggs made in this time, but only a few will survive and evolve into larvae form, which is when the female’s task is complete and the larvae are left on their own in the ocean.

How wonderful is that? As a larvae, a little Japanese spider crab can only do so much. Avoiding predators depends on chance and one’s camouflage abilities, so the stress seems to be low, as there isn’t much responsibility for failure. Failure is just death, after all, how could a larvae hold itself accountable?

I imagine that, if I were an adult Japanese spider crab who had once conceived, I would feel very awkward if I came across a larvae and could only slowly crawl away. It’s a good thing that Japanese spider crabs don’t have good eyesight. Why don’t they have good eyesight or good senses overall? That’s just because they don’t have many predators, so there wasn’t much benefit in having the relevant mutations anyway.

The life of an adult Japanese spider crab is calm and unhurried. They feed off of decaying matter and such, so there is no need to hunt or scheme like most other deep sea creatures. Their temperament is gentle, and so it is very suitable to have them in large on-land aquariums (or so I’ve heard). It is just when they are molting are Japanese spider crabs ever vulnerable.

The hard shell in normal times is the number one factor when it comes to being invulnerable to potential predators. Aside from this, the Japanese spider crab’s legs are delicate and can be easily plucked off by a starving octopus or a passing sea trawler, of which has little consequence, since their limbs are able to regenerate quite well. I wonder why that is. Maybe their legs were farmed in the ages predating history.

I’ve seen a crab pick up another crab’s leg and wave it around menacingly in a supermarket before. What if there was a crab society that did that when communicating? Tear off your leg to show kindness, and then exchange them for friendship or something? But, the life of a Japanese spider crab is like that of a hermit, and even in closed environments these crabs do not seem to communicate nor have the desire to with each other. It seems to be unlikely to have a crab society, unless some massive black event had once happened, forever banning the Japanese spider crab from communicating with its fellows for all of eternity.

If that were the case, maybe Japanese spider crabs once had good senses? But only after committing a taboo did they voluntarily regress their senses and lead a life of solitude. That would be very dramatic if that were the case; good on the Japanese spider crab for keeping its creed for so long.

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