Members of chondrichthyes are thought to be descended from fishes that had
a cartilaginous skeleton
a bony skeleton
mucus glands
slime glands

The correct answer is B. A bony skeleton

Explanation:

In biology, Chondrichthyes are mainly marine jawed fishes that have cartilage skeletons rather than bone skeletons and also they have paired fins, this includes animals such as rays and sharks. In terms of origin, it is believed this type of fishes are mainly linked to placoderms that were a type of primitive fish that lived during the Devonian period that had a body skeleton as they were covered by hard structures called plates made of bone. Because of this, it is believed this structures evolved into less rigid ones made of cartilage although both the primitive fish and modern Chondrictyles share features such as the structure of jaws. Therefore, Chondrictyles descended from fishes that had a bony skeleton.

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b is the correct answer