Monday, January 16, 2017

Eels hold onto prey with their second "alien-like" jaws

Hungry movie aliens are very persistent.
Photo: HadeelMaaitah, Twitter
The xenomorph space alien in the movie "Alien" has that terrifying second set of jaws that pop out to nab its intended victim.

The idea for this bizarre architecture actually came from Earth.

It's real. In an eel. (sorry).

Morays and other eels, and in fact some 30,000 fish species, have these double jaws that normally sit in the animal's throat, rather than in their mouth, like ours do. Their correct name is "pharyngeal" jaws, named for the pharynx, or throat.

Why eels? Well, morays are large predatory fish, growing up to several meters (>10 feet) long. They lack protective scales and pelvic and pectoral fins, so they mostly hang out in narrow burrows waiting to ambush a fish or crab. When they see on pass by close enough, they come out and make an swift attack. They then swallow the animal whole. Gulp.

A Mediterranean moray swimming - note the long body, small head and lack of pelvic and pectoral fins.
That open mouth is for taking in water, not threatening divers!  Photo: Drow_male, Wikipedia

Since they are not going out looking for food, they have to make the most of what passes by - and not miss opportunities.

In this quick video, the second set of jaws of a snowflake moray eel make sure the prey - in this case a crab - doesn't escape:

Morays and other eels are ray-finned fish (as are a majority of fish, including cichlids, tuna, salmon, trout, and goldfish), which have bones inside their fins that keep them stiff and sharp at the ends.

Most use suction to eat -- catching prey by suddenly opening their mouth, and getting the negative water pressure in their mouth cavity to suck the prey in. Their pharyngeal jaws are mostly modified gill bones that help to crush up food after it passes through the mouth.

Pharyngeal jaws of moray eels. Image: Zina Deretsky, NSF
Eels are different -- they bite their prey, without using suction.

That extra set of alien jaws has its own teeth, and it is attached to the mouth by long muscles that match the eel's long thin body.

Researchers that filmed morays at high speed feeding found that the eels first grab a prey fish with the teeth on their front jaws.

In the attacking, those long muscles spring into action, shooting the pharyngeal jaws forward into the mouth to grasp the prey. This second bite keeps the wriggling prey from freeing itself.

The eel can then open its front jaws, releasing the prey, while the muscles controlling the pharyngeal jaws pull them and the prey down toward the stomach.

Moray eels are large, so that second bite helps them secure large prey without have to expand their mouths, which would make burrow-living difficult.

A large green moray swimming in the open toward its next hiding spot. They can reach up to 8 feet (2.5 m) long.
Photo:  P. Lindren, Wikipedia


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