Angustidontus is a genus of predatory pelagic crustaceans from the Late Devonian and Early Carboniferous periods, classified as part of the subclass Eumalacostraca.

Fossils of the genus have been recovered in relative abundance from Canada, Germany, the Czech Republic, Poland, Belarus, Ukraine and large parts of the United States, including Oklahoma, Ohio, Indiana, Kentucky, Montana, Utah, Nevada.

Angustidontus was a predatory angustidontid crustacean, measuring about 6 centimetres (2.4 inches) in length (9 cm, 3.5 in if the large maxillipeds, that is, appendages or "limbs" used for feeding, are counted).

[2] Instead, Angustidontus used the next four pairs of thoracopods (which were short and possessed strong claws and serrated gnathobases, that is, modified and expanded bases to aid feeding) to tear apart prey and transport it to the mouth.

[4] In 1960, Canadian geologists Murray John Copeland and Thomas Edward Bolton considered the fossils to instead represent gill rakers of fish or be "claws similar to those on the second maxilliped of the stomatopod Squilla"; furthermore, the appendage was noticed to have had some kind of "ball and socket" joint type of articulation.

[1] The new specimens allowed researchers to determine that Angustidontus was a peracarid malacostracan crustacean, and that Concavicaris simply represented a separate animal that was part of a larger Late Devonian fauna including a large amount of different invertebrates, such as worms, cephalopods, bivalves, brachipods and sponges.

Angustidontids are diagnosed as eucarids that possess carapaces and stalked eyes with scale-like exopods (the external branch of the two comprising a biramous appendage) on the second antennae, an elongated pleion and a tail fan.

They were all considered synonymous with A. seriatus by British and Polish paleontologists William David Ian Rolfe and Jerzy Dzik in 2006 as fossils of these species presented highly variable patterns.

Fossil animals found in association with Angustidontus are exclusively open sea pelagic creatures, such as conodonts, cephalopods, ostracods, concavicarids and fish.

The bottom regions were likely slightly benthose with a soft and muddy environment; the latter was likely anaerobic and poisonous, with abundant hydrogen sulfide, which would have prevented decomposition and allowed for fossils to be preserved.