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Explanations for Dungeness-crab with barnacles quiz:

The first observation is that the crab must not have moulted for a considerable period. This is likely, as while juvenile Metacarcinus magister may moult several times per year, sexually mature individuals (like this one) moult only annually or biannually. However, if your idea is that this individual has attained "terminal-moult" status, you are probably incorrect. Family Cancridae are thought to moult continuously until death, unlike other families such as Majidae, the spider crabs, that do attain a terminal moult.

The second observation, and a more interesting one, is that the barnacles are able to grow only at the front edge of the carapace, the part exposed to fresh seawater when the individual is buried. Another clue is provided by the nature of the sediments. They are fine-grained and black, and likely to be anaerobic at even shallow depths, thus smothering any barnacle spat that may have settled and attached while the crab was moving above ground.

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