The systematic position of the order Agnostida within the class Trilobita remains uncertain, and there has been continuing debate whether they are trilobites or a stem group.

[5] A 2019 study of adult specimens with preserved soft tissue from the Burgess Shale found that agnostidans shared morphological similarities to trilobites and other related artiopodans like nektaspids, and their placement as stem-crustaceans was unsupported.

They are likely to have lived on areas of the ocean floor which received little or no light and fed on detritus which descended from upper layers of the sea to the bottom.

Recent work suggests that some agnostids were benthic predators, engaging in cannibalism and possibly pack-hunting behavior.

[6] They are sometimes preserved within the voids of other organisms, for instance within empty hyolith conchs,[7] within sponges, worm tubes and under the carapaces of bivalved arthropods,[8] presumably in order to hide from predators or strong storm currents; or maybe whilst scavenging for food.