This group of animals is primarily aquatic and has mandibles and two pairs of antennae. which group is this?
a) insects
b) crustaceans
c) arachnids

The best and most correct answer among the choices provided by the question is the second choice "crustaceans"

Crustaceans form a large, diverse arthropod taxon which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill, woodlice and barnacles.


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It is called the medulla oblongata or people usually call it medulla. it is the lower half of the brain stem continuous with the spinal cord.