Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Stomiiformes
Family: Stomiidae
Genus: Malacosteus
Species M. niger

A small (15-24 cm) scaleless black fish, found living in the deeper parts (500 to 2,000 meters deep) of the oceans, although it is not bottom dwelling (Fun words: it's mesopelagic and bathypelagic, but not benthic). It's limited to tropical and subtropical parts of the oceans, although that far down it's pretty cold anyway.

It has two oddities that make it interesting. First off, it has two photophores (glowing spots); a comma-shaped one directly under the eye, which glows red, and a lower one that glows green. Green and blue photophores are common in deep-sea dwellers; these colors travel the furthest in water, and (probably because of this) most of these deep-sea animals can only see these colors. Red does not travel far, and is not visible to most deep-sea dwellers. The red produced by the stoplight loosejaw is almost infrared, and is only barely visible to the human eye. It is completely invisible to the loosejaw's dinner. The loosejaw can see it just fine. It is probably particularly useful for hunting red-colored shrimp.

So that explains the 'stoplight' part of the name. Now for the 'loosejaw'. Imagine a fish with a really, really big, gapping, humongous mouth. The mouth is bigger than the head -- in fact, the mouth is the head. There's the eye, the glowing spots, and then the mouth. Now, imagine the skeleton of that mouth; arching jawbones, long sharp inward pointing teeth, and giant holes where the cheeks and floor of the mouth should be. Now you've got it. No skin, just bones. If the loosejaw bites down on something, the something is dead. If the loosejaw bites down over something, the something swims away unmolested. (okay, of course it has skin over its bones. But it has no cheeks, no floor to it mouth, and it looks as though it's missing a good part of its throat as well).

This is actually a very sensible way to grow your jaw, if you happen to live underwater. Fewer flaps of skin mean less water resistance, which means a faster snapping speed. The jaws are very mobile, and can be extended out and pulled back in; if the jaws have caught something, they pull it in to a second, smaller set of teeth in the front of the throat. If not, they can try for another lunge while the prey is still reacting.

AKA the rat-trap fish.

Astonishing Animals by Tim Flannery and Peter Schouten

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