''Parastemmiulus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

millipede Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature. Each double-legged segment is a resu ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Stemmiulidae known from a fossil found in Mexico. There is one described species in the genus, ''Parastemmiulus elektron''. The species is one of three millipedes described from

Mexican amber Mexican amber, also known as Chiapas Amber is amber found in Mexico, created during the Early Miocene and middle Miocene epochs of the Cenozoic Era in southwestern North America. As with other ambers, a wide variety of taxa have been found as inc ...

, and the oldest Stemmiulidae fossil species as of 2013.

History and classification

''Parastemmiulus elektron'' was described from a solitary fossil, which is preserved as an

inclusion Inclusion or Include may refer to: Sociology * Social inclusion, aims to create an environment that supports equal opportunity for individuals and groups that form a society. ** Inclusion (disability rights), promotion of people with disabiliti ...

in a transparent chunk of Mexican amber. At the time of description, the amber specimen was housed in the fossil collection of the Instituto Nacional de Antropología e Historia in

San Cristóbal de las Casas San Cristóbal de las Casas (), also known by its native Tzotzil name, Jovel (), is a town and municipality located in the Central Highlands region of the Mexican state of Chiapas. It was the capital of the state until 1892, and is still cons ...

Simojovel Simojovel is one of the 119 municipalities of Chiapas, in southern Mexico. As of 2010, the municipality had a total population of 40,297, up from 31,615 as of 2005. It covers an area of 446.99 km2. The municipality had 145 localities, the ...

. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

fossil is composed of a very complete adult female recovered from the La Guadalupe Quarry. Mexican amber is recovered from fossil bearing rocks in the

region of Chiapas, Mexico. The amber dates from between 23 million years old at the oldest and 15 million years at the youngest. The La Guadalupe Quarry site is an outcrop of amber bearing strata belonging to the Mazantic shale. The deposits preserve a transitional river or stream environments near the coast and preserves fossils of a mangrove forest ecosystem. The holotype was first studied by a team of researchers headed by Francisco Riquelme of the Universidad Autónoma del Estado de Morelos with their 2013

type description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

of the genus and species being published in the natural sciences journal ''

Historical Biology ''Historical Biology'' is a peer-reviewed scientific journal of paleobiology. It was established in 1988, and is published by Taylor & Francis. The journal is edited by Gareth J. Dyke (National Oceanography Centre). Abstracting & Indexing Th ...

''. The genus name is a combination of the genus '' Stemmiulus'' and "para" meaning ''along side'', a reference to the similarities between the two genera. The specific epithet ''elektron'' was is based from the Greek word meaning amber. ''P. elektron'' is one of three millipede species described from Mexican amber, the others being '' Anbarrhacus adamantis'' and '' Maatidesmus paachtun'', while a number of other species have been described from the similarly aged

Dominican amber Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree '' Hymenaea protera''. Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil inc ...

. One possible Stemmulid fossil was described from Dominican amber, however it was not complete, and has been regarded as doubtful. ''P. elektron'' is the first Stemmulid genus described from a fossil.

Description

The ''P. elektron'' female is reddish-brown in overall coloration with the legs a brownish tone that trends to hyaline. The body is composed of forty six segments and has a length of approximately . The ocellar field is shallow and triangular in shape with three

ocelli A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...

, and is positioned just to the rear of the antennae. Two grooved possible sensory canals are present in the field, one connecting the rear and front ocelli, the other connecting the middle ocelli to the antenna socket. Present is a defined, pear-shaped Tömösváry organ located below the antenna socket and reaching the ocellar field. The antennae have a total of eight antennomeres that vary in length. The largest segment is antennomere 2, while the smallest is antennomere 7. The low ocelli numbers, differences in ocelli sizes, and varied antennomere lengths is a combination of characters only found in Stemmiulida. However, in contrast to ''P. elektron'' living species of the family do not have a Tömösváry organ.

References

External links

* {{Taxonbar, from=Q21682645 †Parastemmiulus Prehistoric myriapod genera Fossil taxa described in 2013 Millipedes of North America Miocene arthropods Mexican amber