Final answer:
Anodontia refers to the absence of all teeth, while Oligodontia is the condition of being missing some teeth. Chondrichthyes differ from Osteichthyes by having skeletons made of cartilage instead of bone.
Step-by-step explanation:
The condition where a person is missing all teeth is called Anodontia. If a person is missing some but not all teeth, the condition is termed Oligodontia. When a person has an abnormally low number of teeth, it is known as Hypodontia, and the condition where there are extra teeth beyond the usual number is known as Hyperdontia. When distinguishing between two groups of fish, members of the Chondrichthyes (such as sharks and rays) differ from members of Osteichthyes due to their lack of a bony skeleton. Instead, Chondrichthyes have a skeleton made of cartilage.