And you thought your growing-up years were complicated ...
This video from YouTuber Scipio314 follows a Japanese spider crab (Macrocheira kaempferi) through the weeks-long process of moulting. Because their hard exoskeletons don't grow, crabs and other crustaceans have to shed – they outgrow their skeletons like we'd outgrow our clothes. But it's not as easy for crabs as just jumping out of their skin when the time is right.
Prior to moulting, a crab reabsorbs some of the calcium carbonate from the old exoskeleton, then secretes enzymes to separate it from the underlying skin. Once there's room, the new minerals are used to form a thin, softer skeleton beneath the old one. A day before the crab is ready to ditch its old attire for good, the animal will start to absorb seawater, causing it to swell up. This helps to expand the old shell and causes it to crack along a special seam that runs around the body, at which point the crab can pop out!
These impressively large crabs can reach a maximum length of 13 feet (about four metres), and have a lifespan of around 100 years! Most of that time is spent traversing the seafloor in search of tasty scraps, including algae, plants, molluscs and small fish.
Top header image: Wendell Reed/Flickr
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