''Siphoniulus'' is a poorly known genus of millipede containing only two living species: ''S. alba'' from Indonesia, and ''S. neotropicus'' from Mexico and Guatemala. An additional two fossil species are known from Cretaceous amber. ''Siphoniulus'' species are the only members of the family Siphoniulidae and

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Siphoniulida, making Siphoniulida the smallest millipede order. Few specimens are known, and their classification is contentious, although most recent studies place them as

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

members of the

Helminthomorpha Chilognatha is a subclass of the class Diplopoda, which includes the vast majority of extant millipedes, about 12,000 species. Taxonomy The classification of Chilognatha presented below is based on Shear, 2011, and Shear & Edgecombe, 2010 (extin ...

("worm-like millipedes").

Description

Siphoniulids are small and eyeless. The head is drawn out into a conical beak, and lacks Tömösváry organs. The body is relatively long and narrow, containing up to 51 segments and reaching up to long, and 0.25 mm (0.01 in) wide. The body color ranges from pure white to tan, and has been described as resembling a

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

. The exoskeleton is smooth and has few setae, and

ozopores An ozopore is the opening of a defensive gland present in some arthropods, notably in millipedes of the order Polydesmidagonopods (modified copulatory legs) consisting of the anterior limbs on the seventh segment, and which are partially recessed into the body. The telson (rear-most segment) possesses small bristle-like structures called spinnerets.

Distribution

''S. alba'' is only known from a single specimen collected in 1894 near Maninjau on the Indonesian island of

Sumatra Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent i ...

. ''S. neotropicus'' was discovered near the Mayan ruins of Tikal in Guatemala, and is also known from the Mexican states of

Chiapas Chiapas (; Tzotzil language, Tzotzil and Tzeltal language, Tzeltal: ''Chyapas'' ), officially the Free and Sovereign State of Chiapas ( es, Estado Libre y Soberano de Chiapas), is one of the states that make up the Political divisions of Mexico, ...

and Veracruz. The extinct species ''S. muelleri'' and ''S. preciosus'' are known from Late Cretaceous Burmese amber.

History

''Siphoniulus alba'' (and the family Siphoniulidae) was described in 1894 by

R. I. Pocock Reginald Innes Pocock F.R.S. (4 March 1863 – 9 August 1947) was a British zoologist. Pocock was born in Clifton, Bristol, the fourth son of Rev. Nicholas Pocock and Edith Prichard. He began showing interest in natural history at St. Edward ...

, from a female specimen collected near Maninjau on the island of

.. The specimen was deposited in the Zoological Museum Amsterdam, but by 1975 the specimen was missing its head and anterior segments. ''S. neotropicus'' was described by Richard L. Hoffman in 1979 from two possibly immature females collected in Guatemala. Males of either species were unknown until 2003, when samples of leaf litter from Mexico sorted by researchers at the

Field Museum of Natural History The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educational ...

revealed new specimens of ''S. neotropicus'', allowing for complete anatomical descriptions and characterization of the gonopods.

Classification

Siphoniulids have been classified in various, conflicting placements within the

("worm-like" millipedes) since their initial description, and their relation to the rest of millipedes is still unresolved. When first described, the family Siphoniulidae was placed in the "Suborder"

Colobognatha Colobognatha is a clade (formally considered a subterclass) of helminthomorph millipedes containing four orders: Platydesmida, Polyzoniida, Siphonocryptida, and Siphonophorida. Description The Colobognatha are united by several shared traits ( ...

, a group that is now recognized as a larger grouping including the orders

Platydesmida Platydesmida (Greek for ''platy'' "flat" and ''desmos'' "bond") is an order of millipedes containing two families and over 60 species. Some species practice paternal care, in which males guard the eggs. Description Platydesmidans have a flatte ...

, Polyzoniida, and

Siphonophorida Siphonophorida (Greek language, Greek for "tube bearer") is an order of millipedes containing two families and over 100 species. Description Millipedes in the order Siphonophorida are long and worm-like, reaching up to in length and up to 190 ...

. The following year, the American entomologist

Orator F. Cook Orator Fuller Cook Jr. (May 28, 1867 – April 23, 1949) was an American botanist, entomologist, and agronomist, known for his work on cotton and rubber cultivation and for coining the term "speciation" to describe the process by which new species ...

considered Stemiulids as "suborder Siphoniuloidea", closely related to Julidans and

Spirostreptida Spirostreptida is an order (biology), order of long, cylindrical millipedes. There are approximately 1000 described species, making Spirostreptida the third largest order of millipedes after Polydesmida and Chordeumatida. Description Spirostrept ...

ns (a grouping termed Diplochaeata). In 1979, Hoffman placed Siphoniulida (now considered an order) as Helminthomorph '' incertae sedis'', meaning the placement within Helminthomorphs was undetermined, due to the absence of male specimens.Hoffman RL. (1979) Classification of the Diplopoda. ''Geneve: Mus. Hist. Nat.'' 237 pp. With only two known species, Siphoniulida is the smallest order of millipedes, followed by

Siphonocryptida Siphonocryptida is an order of millipedes, comprising the sole family Siphonocryptidae. With only seven described species, the Siphonocryptida is the second smallest millipede order, surpassed only by Siphoniulida, with two species. Classifica ...

with three to six species. In more recent years, millipedes have been studied by cladistic and modern phylogenetic methods, yet Siphoniulida remains enigmatic. In the first cladistic study of millipedes, Enghoff could only place Siphoniulids as ''incertae sedis'' within the Helminthomorpha, but "probably... a specialized subordinate taxon within some

juliform Juliformia is a taxonomic superorder of millipedes containing three living orders: Julida, Spirobolida, and Spirostreptida, and the extinct group Xyloiuloidea known only from fossils. Morphology The species possess long cylindrical bodies w ...

or colobognathan order". However, in the first morphological study of millipede phylogeny incorporating full details of ''Siphoniulus'' anatomy, Siphoniulida did not appear closely related to the Juliformia nor Colobognatha, but rather appeared as an

outgroup Outgroup may refer to: * Outgroup (cladistics), an evolutionary-history concept * Outgroup (sociology), a social group {{disambig ...

to all other helminthomorphs, and the internal classification of Helminthomorpha was poorly resolved and significantly differed from Enghoff's. In a subsequent study combining anatomical data with

DNA sequence DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...

data from other groups, Siphoniulida again appeared as basal within Helminthomorpha.

Notes

References

External links

A siphoniulid milliped from Central America
Hoffman's 1979 original description of ''Siphoniulus neotropicus'' with photograph and illustrations. {{Taxonbar, from=Q6452569 Millipede genera