Answer:
a swimmeret, which she found on a crab
Explanation:
Crabs are arthropods belonging to the Subphylus (or Superclass) Crustacea, Class Malacostraca and Order Decapoda or Brachyura - which in some classification systems presents as Brachyura Infraord. Such animals have carapace-lined bodies. Very similar to crabs, the difference between them is in their locomotor paws: crabs are paddle-shaped, assisting in swimming; and in crabs, they appear as nails, assisting in terrestrial locomotion. Besides helping locomotion, the front legs of crabs, called swimmers, have an important role in gas exchange and reproduction of these animals. For this reason, we can conclude that the structure that the scientist exposed in the question was observing is a swimmeret, which she found on a crab
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