Evolution occurs in small steps. The members of the genus Inimicus, a group of fish within the subfamily Synanceiinae (Stonefish), use two separated rays of each pectoral fin to crawl over the seabed.
Walking or rather crawling over the seafloor with paired pectoral fins (the first two caudal rays of each pectoral fin are detached from the rest of the fin and move separately) is not limited to species within the genus Inimicus. There are a number of fish species that are able to walk on the seafloor using their pectoral fins.
The best-known species that can regularly be encountered by underwater videographers, underwater photographers, or by scuba divers are batfish, frogfish, and flying gurnards.
Batfish (Ogcocephalidae, not to be confused with spadefish of Ephippidae) use their pelvic and anal fins to support the body off the substrate. These fins also enable batfishes to walk on the seafloor, though the irregular shape of the fins causes most batfishes to swim awkwardly.
Frogfish (Antennariidae) can use both pelvic and pectoral fins as a form of walking or galloping locomotion.
The Flying Gurnard (Dactylopteridae) combines both pelvic and pectoral fins to move over the substrate. Flying Gurnards, however, are good swimmers in comparison with frogfish and batfish.
This type of walking is believed to be a predecessor to the later progress of similar locomotion (crawling, walking, and running) in terrestrial vertebrates.
The species in this underwater video crawling over the substrate is the "Inimicus filamentosus," also known as the Filament-finned Stinger and is endemic to the Western Indian Ocean.
To film small subjects or details of bigger subjects, like the modified fin rays in this clip, it is recommended to use a dioptre. Many underwater housings can be fitted with a flip adapter to hold a wet lens. So that when the occasion arises the switch from your standard lens to a macro lens or dioptre is easily and rapidly realised under water.
The “crawling over sand” sound was added in post-production.
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