A dog presents with a large blackened mass in the oral cavity and the veterinarian suspects melanoma. What type of tumor is a melanoma?

Round cell tumor.

Explanation:

Cancer may be defined as the uncontrolled growth of the cell and the cells grow abnormally and shows less differentiation. The cancer might occur due to the mutation in the tumor suppressor gene.

Round cell tumor represent a type of skin tumor and common in dogs. This tumor is generally marked by the mass of the cell that might be in different colors. Round cell tumor represent the melanoma as this is the cancer of the skin pigment. The symptoms shown by the dog represents the round cell tumor.

Thus, the answer is round cell tumor.