Little is known about H. trolli, because it lives so deep underwater - between 1 mile and 1.3 miles (1,640 to 2,063 meters) under the surface, Lundsten said. Luckily, the videos have helped the researchers gather more clues about these ghost sharks, which measure between 2 feet and 3 feet (0.6 to 0.9 m) long.For instance, the videos show H. trolli swimming over a rocky seafloor, rather than soft sediment, "which is unusual for ratfishes," Lundsten said. "[Ratfishes] are typically found above soft sediment, and the fact that these live in a rocky habitat is unique to this group."
Lundsten added that H. trolli's Frankenstein-like stitches are actually sensory organs that cover the fish's entire body, especially its face. These organs can sense minute movements and vibrations in the surrounding water, which helps the fish hunt prey, said Dave Ebert, who co-authored the study with Lundsten and Amber Reichert, a graduate student of marine science at California State University (Cal State). Ebert is also the program director of the Pacific Shark Research Center at Cal State's Moss Landing Marine Laboratories.
In addition, male ratfish "have a strange sexual-related organ that's on the top of their head," Lundsten said. "It's a club-shaped thing that has spines on it, and it's used for grasping and better positioning the female during copulation." [The 9 Weirdest Animal Penises]
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Ratfishes have cartilaginous skeletons, indicating they're related to rays and sharks. Just like their relatives, ratfishes have a long history. Paleontologists have found ratfish fossil remains dating from about 350 million to 375 million years ago, showing that the fishes predate the dinosaur age, Didier told Live Science in March 2016.
Earlier this year, another type of ratfish, known as a knifenose chimaera (Harriotta raleighana), caught the public's attention when one ended up in the bycatch of a fishing boat off the coast of Nova Scotia, Canada.
Moreover, there are likely more unknown ratfish out there, Ebert said. Since 2002, researchers have discovered 19 new ratfish species, including the Pacific black ghost shark (Hydrolagus melanophasma), captured on video in the Gulf of California, Mexico, by MBARI in 2003.