Xanthidae is a family of crabs known as mud crabs, pebble crabs or rubble crabs. Xanthid crabs are often brightly coloured and are highly poisonous, containing toxins which are not destroyed by cooking and for which no antidote is known. The toxins are similar to the tetrodotoxin and saxitoxin produced by puffer fish, and may be produced by bacteria in the genus Vibrio living in symbiosis with the crabs.
Both saxitoxin and tretrodotoxin are so incredibly toxic, that as little as half of a milligram is capable of killing an average sized adult. The toxins are also heat stable and will persist in the tissues despite being cooked. Saxitoxin is the primary toxin involved in paralytic shellfish poisoning, which is often caused by people eating mussels or oysters that have consumed toxic algae. Intriguingly, saxitoxin is listed as a grade one chemical weapon under the UN Chemical Weapons Convention and was reputedly used by the CIA in suicide pills.
Tetrodotoxin on the other hand is famously found in the Japanese puffer fish, a delicacy known as “fugu” which only the most skilled chefs are licensed to prepare. Both chemicals are neurotoxins, affecting the nervous system, resulting in paralysis by shutting down the nerve cells’ ability to transmit information.
The toxins are in the flesh and cannot be transmitted if one is pinched by the claws. Most of poisonous crabs have very bright warning colours, and it is a good practice to avoid eating them.
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