Hypostome (trilobite)

The hypostome can be classified into three types based on whether they are permanently attached to the rostrum or not and whether they are aligned to the anterior dorsal tip of the glabella.

Either side of the median body is a border with various extensions, including anterior and posterior wings, sometimes bearing knob-like processes.

Natant hypostomes appear to have been conservative over the course of the evolution of trilobites[2] with overall form and shape of a simple ovoid without posterior extensions or ornamentation.

[4] A conterminant hypostome is attached to the anterior doublure, aligned with the front edge of the glabella and found on trilobites thought of as predators.

Many impendent hypostomes have prongs, grooves and other adaptations thought to relate to feeding on complex food sources.