Thysanuran

The best known and most often seen thysanurans are the two domesticated species: silverfish and firebrat.

As insects go, thysanurans are about as primitive as an arthropod can get and still be considered an insect.

2008, Timothy J. Bradley, Saline-water Insects: Ecology, Physiology and Evolution, Jill Lancaster, Robert A. Briers, Aquatic Insects: Challenges to Populations: Proceedings of the Royal Entomological Society's 24th Symposium, page 22, Marine thysanurans are another abundant and highly successful group of apterygotes able to exploit the ocean shore.