Kreature Feature started off as an educational presentation at our monthly general staff meetings here at the Two Oceans Aquarium. Now in its fourth month and increasingly popular among Aquarium staff, we decided it’s only right to extend the knowledge and fun to our readers here on our website. Every month PA to Head of Education Katja Rockstroh presents a different animal that we have here at the Aquarium and tells our colleagues more about it. Usually she uncovers some rather interesting facts about the various animals she researches. She also makes sure to entertain her co-workers …

When you google “world’s largest animal”, various results will come up, like the blue whale or the ostrich. But when you google “largest crustacean”, you will find the spider crab.

The spider crab has various common names. You can just call it the spider crab; you can also call it the Japanese spider crab or giant spider crab. Or if you feel that those names are not descriptive enough, why not go with Japanese giant spider crab. Crabs of all sorts belong to the sub-phylum Crustacea, along with lobsters and shrimp. The phylum they belong to is Arthropoda and this includes animals such as bees, fleas and spiders.

A giant spider crab at Kaiyukan Aquarium in Osaka, Japan. Photo courtesy Flickr/Takashi Hososhima (licensed under CC BY-SA 2.0)
 

In the scientific world, the spider crab is called Machrocheira kaempferi. Machrocheira means “large” or “overconstructed”, which becomes quite evident just by looking at the animal. This animal is like the daddy longlegs of the oceans, but with 10 legs instead of eight.

The species name kaempferi commemorates Engelbert Kaempfer, a German naturalist and physician who mainly studied and classified plants in Japan. The spider crab also has two main Japanese names. One is taka-ashi-gani, which means “long legs”. The second is shinin-gani, which translates to “dead man’s crab”. This name is derived from a Japanese folklore, which describes the crab as a monster lurking in the kelp, waiting for a diver or sailor to come along. The crab then grabs the victim, drags them underwater and proceeds to feed on their decaying body. Charming.

What do they actually feed on? Molluscs, like clams and mussels, and dead stuff (but not dead humans). Here is a video of a spider crab feeding on a white mussel.

As mentioned earlier, the spider crab is the largest crustacean in the world. But this is relative to its leg span only, as there is a smaller but heavier crustacean on this planet: the American lobster. They can weigh up to 20kg! The spider crab can weigh up to 19kg, however it is the leg span that is its most amazing characteristic. From cheliped to cheliped (i.e., the two front legs with a little claw), they can grow up to 3.8m.

A crab specimen from the American Museum of Natural History circa 1920 measures 3.6m across its outstretched legs. Photo courtesy Wikipedia
 

Like all crustaceans, the spider crab needs to moult. This essentially means that it needs to renew its outer skeleton, also called the exoskeleton, in order to grow. The process can take hours and makes the animal extremely vulnerable to predation, as its soft, unprotected flesh becomes exposed.

Here at the Two Oceans Aquarium, when a spider crab moults, we separate the moulting animal from the rest, as cannibalism is known to occur.

 

Spider crabs come from Japan. In fact, that is where ours come from too. Tokyo Sealife gave us our spider crabs in exchange for some ragged-tooth sharks many years ago. They are deep sea animals and live in depths of up to 200m. When they mate, they migrate to “shallower” waters of 50m. During mating season there is an outright ban in Japan on catching spider crabs. And while their numbers are declining, they are not vulnerable or endangered. They have not been evaluated in terms of their conservation status, possibly because they are very hard to study, since they live so deep down in our oceans.

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