Final answer:
Crustacean appendages are typically two-branched and are correctly described as b) biramous, which refers to their evolutionary ancestral form. These appendages are significant for movement and environmental interaction, and the term biramous is the correct answer to the multiple-choice question.
Step-by-step explanation:
Most appendages of crustaceans are two-branched, or biramous. Option b, biramous, is the correct term to describe crustacean appendages that are formed in two parts known as endopods and exopods. This is distinct from uniramous appendages that are one-branched, typical of myriapods and hexapods. The biramous nature of the appendages in crustaceans is reflective of an ancestral condition in arthropods and is crucial for various functions, including locomotion and sensing the environment.
For instance, the antennae of crustaceans, which are also considered appendages, are often biramous and serve both sensory and locomotive functions. Crustaceans also have a specialized body structure, including a cephalothorax and an abdomen, amongst other characteristics. Barnacles, which are crustaceans, show sessile behavior and do not have the typical biramous appendages; instead, they have modified feeding appendages.