The head is small with a large jaw and appears haggard, riddled with mucous cavities delineated by serrated edges and covered by a thin skin.

In adults, the largest two fangs of the lower jaw are so long, the fangtooths have evolved a pair of opposing sockets on either side of the brain to accommodate the teeth when the mouth is closed.

According to BBC's Blue Planet, episode "The Deep", the fangtooth has the largest teeth of any fish in the ocean, proportionate to body size, and are so large, they can never close their mouths.

[4] Unlike many other fish, the fangtooth's large, fang-like teeth are permanently attached to their jaw bones without replacement.

[6] The smaller teeth and longer gill rakers of juveniles suggest they feed primarily by filtering zooplankton from the water, while the deeper-living adults target other fish and squid.

viperfishes, daggertooths, bristlemouths, barracudinas, anglerfishes), thought to be an advantage in these lean waters where anything encountered (even if it is larger than the fish) must be considered a possible meal.