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14 The Orders of Insects: Archaeognatha and Zygentoma

Archaeognatha [Photo: K. Schulz, CC BY 2.0, Wikimedia Commons].
Cladogram with Zygentoma and Archaeognatha highlighted.
Cladogram highlighting Zygentoma and Archaeognatha. Adapted from Gullan, PJ & Cranston PS (2014). The insects: an outline of entomology (5th ed.). Wiley Blackwell.

Order Archaeognatha

Order Archaeognatha

  • common name: jumping bristletails
  • a primitive order whose members were once assigned to the Thysanura.
  • scientific name (archaeo = old; gnatha = jaw) refers to primitive condition of mandible articulation
  • feed on algae, moss, lichens and detritus
  • found in damp environments under bark, stones, crevices, leaf litter.
  • typically nocturnal
  • fast and able to jump by flexing their abdomens
  • No direct mating; transfer of sperm is indirect, stalked spermatophore in Aust. spp.
  • moulting continues after adult ecdysis: long lived: 2-4 years

 

Characteristics of Archaeognatha

Adults

  • elongate, laterally compressed body; moderate size 6-25mm; body covered in pigmented scales
  • large, contiguous compound eyes and three ocelli; mouthparts hypognathous (directed downwards) with monocondylar (single-articulated) mandibles; antennae segmented
  • thorax strongly arched; wingless
  • some abdominal segments have paired styles and vesicles
  • abdomen has three “tails”:  a pair of short cerci with a longer, single median caudal appendage

Immatures

  • Resemble a small adult

Order Zygentoma (Thysanura)

Order Zygentoma

  • common names: silverfish or firebrats 
  • named silverfish because as insects move quickly, scales of body shimmer like a silver fish.
  • firebrats are the ones that prefer warmer places 32-44°C.
  • Greek (thysanos = fringe, oura = tail)
  • worldwide distribution; nearly 400 species
  • mainly omnivorous or herbivorous; can digest cellulose
  • domestic species of silverfish feed predominantly on dry paper products, book bindings, wallpaper, household debris
  • found in soil, leaf litter, under bark, dark place; nocturnal
  • an unusual trait: some silverfish moult after sexual maturity, which is attained between 10th and 14th in-star
photo of a silverfish (Zygentoma)
Zygentoma [Photo: Paethon, CC BY-SA 4.0, Wikimedia Commons].

Characteristics of Zygentoma

Adults

  • Elongate, flattened body covered in silvery scales; 5-30mm long
  • mouthparts hypognathous or prognathous (directed downwards or forwards); eyes are absent or greatly reduced; antennae slender, filiform
  • wingless
  • some abdominal segments have ventral styles; abdomen has three “tails”: two paired cerci and a slightly longer median caudal appendage.
  • Metamorphosis simple: ametabolous; long lived: 2-3 years 

Immatures

  • Resemble small adults

Topic Review

Do you know…?

  • the two orders of primitively wingless insects?
  • special features of each order

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