Deep on the floor of the northern South China Sea, a fish with a body like a shrimp and rake-like feelers on its snout was filmed doing something no fish had ever been documented doing before: walking backward. The deep sea is hard to study directly, so most of what scientists know about animals that live there comes from brief glimpses like this one, caught on camera during a handful of dives.<\/p>\n
Researchers from Sun Yat-sen University and the Southern Marine Science and Engineering Guangdong Laboratory in Zhuhai used remotely operated and crewed submersibles to film the armored searobin, Scalicus engyceros, scuttling sideways and in reverse across the seafloor. The species has been known to science since 1872. This is the first time anyone recorded it moving this way, according to the study<\/a>.<\/p>\n Legs Made From Fins<\/p>\n The nickname \u201cfish-prawn hybrid\u201d comes from American media coverage, not from marine biologists, and it isn\u2019t quite accurate: the armored searobin is a true fish, not a cross between two animals. What gives it that shrimp-like look are specialized, free-moving rays that extend from its pectoral fins, operating almost independently of one another like a set of stiff little legs, researchers explain<\/a>.<\/p>\n Han Tian, the study\u2019s lead author and a doctoral researcher at Sun Yat-sen University, says those fin-rays let the fish walk much the way a crab or shrimp does, even though the underlying body plan is entirely fish. The pectoral fins themselves have flattened into rounded, fan-like plates that help the animal balance while it moves and forages along the bottom.<\/p>\n The team filmed three species of armored searobin in different parts of the northern South China Sea: Scalicus engyceros, Paraheminodus murrayi and Peristedion liorhynchus. Only Scalicus engyceros was seen walking sideways and backward, a type of movement the researchers say had never been recorded in any fish species before, according to Discover Wildlife<\/a>.<\/p>\n Finding three related species occupying different spots in the same general region also hints that each may have adapted slightly differently to its own patch of seafloor, something the team wants to investigate further. Han Tian called the discovery a \u201cparadigm-shifting revelation\u201d for how scientists think about which fish are capable of true walking, not just hopping or skittering along the bottom.<\/p>\n Why the Structure Exists<\/p>\n The armored searobin\u2019s snout carries paired, rake-shaped appendages that it uses to sense and probe the sediment for buried prey, and the walking fin-rays appear to serve a similar purpose. Han Tian describes the setup as awkward for getting around quickly, but useful for exactly the kind of slow, deliberate searching the fish needs to do to find food hidden in the seafloor, including digging directly into the sediment surface.<\/p>\n