Symphyla

Symphyla Temporal range: 99–0  Ma PreꞒ Ꞓ O S D C P T J K Pg N Mid Cretaceous to Present
Scutigerella sp. (Scutigerellidae)
Scollopendrellid symphylan (Scolopendrellidae)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Myriapoda
Class:	Symphyla Ryder, 1880
Families
Scutigerellidae Scolopendrellidae

Symphylans, also known as garden centipedes or pseudocentipedes, are soil-dwelling

Symphyla are small, cryptic myriapods without eyes and without pigment.^[4] The body is soft and generally 2 to 10 millimetres (0.08 to 0.4 in) long, divided into two body regions: head and trunk.^[4] An exceptional size is reached in Hanseniella magna, which attains lengths of 25 to 30 mm (1.0 to 1.2 in).^[11]

The head has long, segmented

The trunk comprises 15–24 segments, which are protected by overlapping dorsal plates. Ten or twelve segments bear legs. The first segment is large and usually provided with a pair of legs, the last segment is slender, lacks legs, and possesses a pair of cerci. Symphylans have been reported as living up to four years, and moult throughout their life.^[2] Immature individuals have six pairs of legs on hatching, but they add an additional pair at each moult until the adult instar, which usually has twelve pairs of legs.^[12][13] This mode of development is known as hemianamorphosis.^[14] Although most adult symphylans have twelve leg pairs, the first pair is absent or vestigial in some species (e.g., those in the genus Symphylella), so adults in some species have only eleven leg pairs.^[15][16]

Symphylans have several features linking them to early insects, such as a labium (fused second maxillae), an identical number of head segments and certain features of their legs.^[1] Each pair of legs is associated with an eversible structure, called a "coxal sac", that helps the animal absorb moisture, and a small stylus that may be sensory in function. Similar structures are found in the most primitive insects.

Symphylans breathe through a pair of

The genital openings are located on the fourth body segment, but the animals do not copulate. Instead, the male deposits 150 to 450 packages of sperm, or spermatophores, on small stalks. The female then picks these up in her mouth, which contains special pouches for storing the sperm. She then lays her eggs, and attaches them to the sides of crevices or to moss or lichen with her mouth, smearing the sperm over them as she does so. The eggs are laid in groups of eight to twelve.^[2]

Symphylans also have spinnerets whose secretions turn into a silk-like thread.^[18] One fossil species, Symphylella patrickmuelleri, was found preserved in Burmese Amber releasing long threads of silk.^[19] The silk plays a role in reproduction: the male deposits up to 450 spermatophores on stalks of silk.^[20] Symphylans have also been reported releasing silk as a defense^[21] and to suspend themselves in the air.^[2]

Fossil record and evolution

The symphylan fossil record is poorly known, with only five species recorded, all placed in living genera. The oldest records of both families are found in Burmese amber from the middle Cretaceous, approximately 99 million years ago. As a result, both families are thought to have diverged before the end of the Mesozoic Era.^[22][23][24]

Despite their common name, morphological studies commonly place symphylans as more closely related to

Further reading

• C. A. Edwards (1990). "Symphyla". In Daniel L. Dindal (ed.). Soil Biology Guide. New York: Wiley. pp. 891–910.
  ISBN 978-0-471-04551-9
  .
• U. Scheller (1961). "A review of the Australian Symphyla (Myriapoda)". Australian Journal of Zoology. 9 (1): 140–171.
  doi:10.1071/ZO9610140
  .
• U. Scheller (1982). "Symphyla". In Sybil P. Parker (ed.). Synopsis and Classification of Living Organisms. New York: McGraw-Hill. pp. 688–689.
  ISBN 978-0-07-079031-5
  .
• R. J. Tillyard (1930). "The evolution of the class Insecta". Papers and Proceedings of the Royal Society of Tasmania. 1930: 1–89.

External links

Wikimedia Commons has media related to Symphyla.

• Data related to Symphyla at Wikispecies