Final answer:
Chondrichthyes differ from Osteichthyes by having a cartilaginous skeleton compared to the bony skeleton found in Osteichthyes. This allows them distinct advantages in motion and buoyancy in their aquatic environments.
Step-by-step explanation:
Members of Chondrichthyes differ from members of Osteichthyes by having a cartilaginous skeleton. Chondrichthyes, such as sharks, rays, and skates, have skeletons made of cartilage, which is a flexible and lightweight material, as opposed to the bony skeletons found in Osteichthyes. Cartilage allows Chondrichthyes a different range of motion and buoyancy. The group Osteichthyes includes bony fishes which have a robust skeleton made of bone.
In contrast, Osteichthyes or bony fishes, have various distinguishing features including a bony endoskeleton, overlapping scales, and a protective flap over their gills called an operculum. Bony fishes also have a swim bladder for buoyancy control, which is not found in Chondrichthyes. Consequently, the correct answer to the question is that members of Chondrichthyes differ from members of Osteichthyes by having a (c) cartilaginous skeleton.