Which two of these characteristics are examples of endoskeletons?

scales in fish

bones in mammals

calcium-rich plates in echinoderms

appendages in arthropods

Endoskeletons are bony forms on the inside of the body of an organism. In these cases, fish scales and bones on a human are inside the skin. These would be endoskeletal in nature. Echinoderms with plates and arthropods with appendages would be examples of exoskeletons.