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Narwhal has the strangest tooth in the sea
"Sometimes called the unicorn of the sea, the male narwhal's tusk is actually a tooth, and it grows directly through the whale's upper lip instead of pushing the lip aside."

Sensory ability in the narwhal tooth organ system
"The erupted tusk of the narwhal exhibits sensory ability. The hypothesized sensory pathway begins with ocean water entering through cementum channels to a network of patent dentinal tubules extending from the dentinocementum junction to the inner pulpal wall."

Unicorn of the Sea: Narwhal Facts
"Often dubbed the unicorns of the sea, narwhals are strange and beautiful creatures with long tusks protruding from their heads. Members of the population of more than 80,000 can weigh up to 4,200 pounds and grow as long as 17 feet in length."