Thysanura

Thysanura Temporal range: Late Carboniferous–Recent PreЄ Є O S D C P T J K Pg N
A silverfish, Lepisma saccharina
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Subclass:	Apterygota
Order:	Zygentoma Börner, 1904
Families
Lepismatidae Nicoletiidae Lepidotrichidae Maindroniidae Protrinemuridae

Thysanura is the now deprecated name of an order of the class insecta. The current name is Zygentoma and encompasses the silverfish or fishmoths, and firebrats. Members of the order are best known for their three long caudal filaments.

The superfamily Machiloidea (families Machilidae and Meinertellidae), the jumping bristletails, were included in the Thysanura until the late twentieth century, but then were allocated to their own order Archaeognatha. The remaining members of the Thysanura comprised the suborder Zygentoma; the suborder was raised to full order status, thereby rendering the term "Thysanura" redundant, leaving Zygentoma as the applicable name. However, the momentum of nearly two centuries of nomenclature has preserved the name Thysanura in common use and in much published material.

Etymology

The name Thysanura is derived from the Greek θυσάνος, thysanos for fringe, tassel, bristle and οὐρά, oura for tail, a reference to the three fanned out caudal filaments.

Description and ecology

Silverfish are so called due to the silvery glitter of the scales covering their bodies. Their movement is "fish-like" and makes it look as if they are swimming. They are less than 1 centimetre (0.39 in) long, and found in damp corners or amongst books and paper in houses.

Silverfish have flattened bodies and may be elongated or oval in shape. They have flexible antennae and small or absent compound eyes. They have short mandibles and relatively unspecialised mouthparts. Many species also have a number of short appendages on their abdominal segments, but the most distinctive feature of the group is the presence of three long, tail-like filaments extending from their last segment. The two lateral filaments are formed from the abdominal cerci.

Silverfish may be found in moist, humid environments or dry conditions, both as free-living organisms or nest-associates. They feed on cereals, paste, paper, starch in clothes, rayon fabrics and dried meats. Silverfish can sometimes be found in bathtubs or sinks at night, as they have difficulty moving on smooth surfaces and so become trapped. Wild species often are found in habitats such as caves, and some are commensals living in association with ant colonies, e.g., Trichatelura manni.

There are no current species formally considered to be at conservation risk, though several are troglobites limited to one or a few caves or cave systems, and these species run an exceptionally high risk of extinction.

Families

Lepismatidae is the largest family, widespread with more than 200 species, many living in human habitations. The Nicoletiidae are small and live in soil litter, humus and under stones. The Lepidotrichidae are represented by two species: Lepidotrix pilifera from Baltic amber and Tricholepidion gertschi from forests of northern California. Three species of Maindroniidae are found in the Middle East and in Chile. The Ateluridae (sometimes treated as a subfamily Atelurinae within the Nicoletiidae) live in nests of ants and termites and are small and blind.

Reproduction

Silverfish have an elaborate courtship ritual to ensure exchange of sperm. The male spins a silken thread between the substrate and a vertical object. He deposits a sperm packet (spermatophore) beneath this thread and then coaxes a female to walk under the thread. When her cerci contact the silk thread, she picks up the spermatophore with her genital opening. Sperm are released into her reproductive system, and then she ejects the empty spermatophore and eats it.

Silverfish continue to moult throughout their life, with several sexually mature instars, unlike the pterygote insects. They are relatively slow growing, and lifespans of up to four years have been recorded.

References

• Charles A. Triplehorn and Norman F. Johnson, Borror and DeLong's Introduction to the Study of Insects, 7th edition (Thomas Brooks/Cole, 2005), pp. 177–180
• Firefly Encyclopedia of Insects and Spiders, edited by Christopher O'Toole, ISBN 1-55297-612-2, 2002

External links

• Thysanura – Tree of Life Web Project
• Virginia Extension Service Article