natant

A natant hypostome is not attached to the anterior doublure, with support assumed to be provided by a non-mineralised membrane.

Species of the family Salviniaceae are natant (floating), while those of the family Marsileaceae are rooted.

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

However, the natant species may temporarily grow on wet mud during times of low water, and the Marsileaceae may grow as emergent species, depending on species and location.

Natant hypostomes are thought to be ancestral to other hypostome forms and thought to belong to trilobites with generalized particle feeding habits (i.e. little need to modify mouth-parts to deal with specialized food items).