原尾目 通称为螈或原尾虫，学名蚖。是一类体形微小的无翅昆虫。是昆虫纲中较原始的类群，起源很早，很可能与蛛形类、结合类、甲壳类等节肢动物具有共同的早期祖先。

原尾目昆虫身体细长，长0.5～2mm，呈淡白或黄色。头部为锥形，口器内颚式，无触角，具假眼一对和形状各异的下颚腺一对。前胸足长大，生有许多感觉器，行动时举在前方，有触角的功能。跗节互节，单爪。腹部12节，第1至第3节各有一对退化的小型腹足(刺突)，近腹部后端分别有雌性或雄性外生殖器，没有尾须。

原尾目昆虫的若虫5龄。1龄若虫腹部仅9节，口器和腹足不发达；第2龄若虫肛器和腹足发达，腹部仍为9节；第3龄若虫腹部10节：第4龄若虫腹部12节；第5龄为成虫前期，其后再脱皮变为成虫。1年可发生数代，多以成虫越冬。

The Protura, or proturans, and sometimes nicknamed coneheads, 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. Some evidence indicates the Protura are basal to all other hexapods, although not all researchers consider them Hexapoda, rendering the monophyly of Hexapoda unsettled. Uniquely among hexapods, proturans show anamorphic development, whereby body segments are added during moults. Szeptycki (2007) lists a total of 731 described species worldwide, in seven families, nearly 300 of which are contained in a single genus, Eosentomon.