A White-banded Cleaner Shrimp (Lysmata amboinensis) disappears almost completely inside the throat of a Yellowmouth Moray Eel (Gymnothorax nudivomer).
Morays have a second pair of jaws deep inside their throat that is used to pull prey into their gullet. The mechanism works as follows: the moray grabs its prey with its normal jaws (also called oral jaws), just like any other fish would do (except for those that gape and suck to swallow their prey whole). Once this happens, the moray brings its pharyngeal jaws forward and bites down on the prey to grab it. Then the pharyngeal jaws retract, pulling the prey down the oesophagus (the tube that connects the throat to the stomach) into the moray eel's gullet so that the prey can be swallowed. Like typical jaws, these “pharyngeal” jaws are equipped with teeth on top and bottom. Pharyngeal jaws vary in shape depending on what the fish eats and are believed to have evolved from modified gill arches.
Moray eels have long, elongated bodies perfectly adapted to living and hunting their prey in narrow rock crevices, small overhangs, and in-between the branches of corals. When a moray grabs its prey, it often does so from the safety of its nook, retreating immediately in this narrow space to swallow its spoils. Due to the limited space, the moray is often not able to expand its mouth wide enough to swallow its prey, unlike most fish that expand their mouths and throats to generate an inward suction force. Millions of years of evolution came slowly with the perfect tool to do so; the pharyngeal jaws.
Morays are not the only species of fish equipped with this alien-looking grabbing apparatus; cichlids (Cichlidae), a group of freshwater fish living mainly in Africa's big lakes (Lake Victoria, Lake Tanganyika, etc.), also possess pharyngeal jaws.
In 1979, the film “Alien,” directed by Ridley Scott with Sigourney Weaver in the leading role, was released. In this science fiction film, a space vessel crew had to fight an alien monstrous creature that, just like the moray eel, possessed pharyngeal jaws. For most people at that time, including myself, it seemed like a far-fetched and unrealistic concept created just to impress the viewers even more. However, knowing what I know today, this anatomical item seems much more realistic than it did at that time.
Unfortunately, it is impossible to tell from these underwater images if the cleaner went deep enough to clean these hidden jaws and teeth. But let's just assume it did.
To create the idea of the shrimp going deep into the moray’s throat a reverberating sound effect was added to the sound of moving pereiopods (the shrimp’s walking legs). The sound produced by the shrimps walking legs crawling over the moray’s mouth and throat’s soft tissue to find its way to the pharyngeal jaws would assumably not produce enough sound to make it audible for humans. However, the added effect will help create a more immersive experience for the audience by enhancing the perceived realism of the scene.
This technique is often used in film and animation to heighten the impact of certain actions or events. By manipulating sound in this way, underwater videographers can draw the viewer deeper into the story and create a more engaging experience overall. The use of sound effects can also help to convey important information to the audience, such as the size and scale of the creatures involved, or the intensity of their movements.
This short underwater videoclip has been filmed in Mauritius 🇲🇺
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