''Tricholepidion'' is a genus of wingless insect belonging to

Zygentoma Zygentoma are an order in the class Insecta, and consist of about 550 known species. The Zygentoma include the so-called silverfish or fishmoths, and the firebrats. A conspicuous feature of the order are the three long caudal filaments. The t ...

(

silverfish The silverfish (''Lepisma saccharinum'') is a species of small, primitive, wingless insect in the order Zygentoma (formerly Thysanura). Its common name derives from the insect's silvery light grey colour, combined with the fish-like appearanc ...

and allies), with only a single described species ''T. gertschi'', native to the northern coast of California in Western North America. It lives under dead bark and in rotting wood of conifers in

mesophytic Mesophytes are terrestrial plants which are adapted to neither particularly dry nor particularly wet environments. An example of a mesophytic habitat would be a rural temperate meadow, which might contain goldenrod, clover, oxeye daisy, and '' Ros ...

forests. It is alternatively considered the only living member of the family

Lepidotrichidae Lepidotrichidae is a family of basal insects belonging to the order Zygentoma ( silverfish and allies). The family contains the extinct '' Lepidotrix'', known from specimens preserved in Eocene-aged European amber. The extant Extant or Least ...

, which also includes '' Lepidotrix'' from

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

aged European amber, or the only member of the family Tricholepidiidae. The taxonomic position of ''Tricholepidion'' is uncertain, in some

molecular phylogenetics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies it has been recovered as less closely related to flying insects (Pterygota) than the rest of Zygentoma is, rendering Zygentoma

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

. Each compound eye contains ~40 ommatidia, and they have three ocelli. Scales on the body are absent. Unlike

Archaeognatha The Archaeognatha are an order of apterygotes, known by various common names such as jumping bristletails. Among extant insect taxa they are some of the most evolutionarily primitive; they appeared in the Middle Devonian period at about the sa ...

and the other families of Zygentoma, which have three- and sometimes two-segmented tarsi, they have five-segmented tarsi like many winged insects. As ''T. gertschi'' is the only member of its family still extant, it is considered to be a "living fossil".

References

Further reading