Crustacea dafination?

a large group of mainly aquatic arthropods which include crabs, lobsters, shrimps, woodlice, barnacles, and many minute forms. They are very diverse, but most have four or more pairs of limbs and several other appendages

Explanation:

b.have there own function.

that would be called plucking : )

explanation:

''plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". as a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock."