"If you are human, you might believe that teeth belong in the mouth. If you are a fish, you already know better. You know that teeth belong in the skin too. These teeth are fittingly called dermal denticles: skin teeth. (Mouth teeth are just called teeth, a testament to how the teeth brand has historically hitched its horse to mouths.)"
"The spotted ratfish, Hydrolagus colliei, is a cartilaginous fish. It grows about two feet long and, despite one of its nicknames, is not a shark. Ratfish and other chimaeras diverged from sharks approximately 400 million years ago, and as such, they look a little strange. Karly Cohen, a marine biologist at the University of Washington Friday Harbor Laboratories and an author on the new paper, first saw a ratfish in the San Juan Islands in 2018."
"Ratfish have thin and tapering tails and their brownish bodies are pleasantly dappled in fawn-like spots. Even more anatomical eccentricities lurk inside the fish. While sharks have conveyor belts of individual mouth teeth, ratfish have teeth plates used for grinding. But somewhere between the ratfish's eyes sits a small white bump. This is the tenaculum, a retractable rod tipped with a chandelier of teeth."
The spotted ratfish (Hydrolagus colliei) is a two-foot-long cartilaginous fish distinct from sharks, having diverged about 400 million years ago. The fish glides with thin tapering tails and brownish bodies dappled in fawn-like spots. Ratfish lack shark-style conveyor-belt mouth teeth and instead have broad tooth plates for grinding. The skin also bears dermal denticles—tooth-like structures. Males have a forehead-mounted tenaculum, a retractable rod tipped with numerous teeth used to grasp females during mating, aided by pelvic claspers. The tenaculum appears as a small white bump when retracted.
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