33 Apterygota – Zygentoma

Zygentoma (=Thysanura)

The order Zygentoma (“zyg” = “bridge”, “entom” = “insect”) or Thysanura (“thysan” = “fringe”, “ura” = “tail”), the silverfish, superficially resemble the Archaeognatha. They have flatter bodies, smaller eyes, and dicondylic mandibles with two points of articulation with the head. There are ~370 species worldwide, with 18 species in three families in North America.

Silverfish are more dorsoventrally flattened than the Archaeognatha, and the tarsi are three- to five-segmented. Ocelli are present, but the compound eyes are much smaller than those of the Archaeognatha and are sometimes absent. The two cerci are far longer in the silverfish than in the jumping bristletails, and the caudal filament is long as well.

We rarely collect these animals, although they occasionally show up in e.g. ground floor suites. They are soft-bodied, so must be preserved in ethanol. Our specimens are becoming rather battered, but note the long (broken!) cerci, caudal filament, and antennae as well as the small compound eyes.