Final answer:
The narwhal is a marine mammal with a dark body, spots, a single tusk, and a tail that is half the length of its body.
Step-by-step explanation:
The characteristics described in the question fit the description of the narwhal. The narwhal is a marine mammal that has a single tusk originating from its head. It has a dark body with spots and its tail is half the length of its body. The narwhal also has tail fins that extend horizontally from its body, in addition to the tusk.
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