Protura

The Protura, or proturans, and sometimes nicknamed coneheads,[2][3] are very small (<2 mm long), soil-dwelling animals, so inconspicuous they were not noticed until the 20th century. The Protura constitute an order of hexapods that were previously regarded as insects, and sometimes treated as a class in their own right.[1][4][5]

Protura
Acerentomon species under stereo microscope
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Entognatha
Order: Protura
Silvestri, 1907
Families [1]

Acerentomata

Eosentomata

Sinentomata

Some evidence indicates the Protura are basal to all other hexapods,[6] although not all researchers consider them Hexapoda, rendering the monophyly of Hexapoda unsettled.[7] Uniquely among hexapods, proturans show anamorphic development, whereby body segments are added during moults.[8]

There are close to 800 species, described in seven families. Nearly 300 species are contained in a single genus, Eosentomon.[1][9]