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Siphoniulids have been classified in various, conflicting placements within the [[Helminthomorpha]] ("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]], a group that is now recognized as a larger grouping including the orders [[Platydesmida]], [[Polyzoniida]], and [[Siphonophorida]].<ref name="Pocock1894" /> The following year, the American entomologist [[Orator F. Cook]] considered Stemiulids as "suborder Siphoniuloidea", closely related to [[Julida]]ns and [[Spirostreptida]]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.<ref>Hoffman RL. (1979) Classification of the Diplopoda. ''Geneve: Mus. Hist. Nat.'' 237 pp.</ref>{{efn|Gonopod morphology is one of the primary diagnostic traits in millipedes.}}
Siphoniulids have been classified in various, conflicting placements within the [[Helminthomorpha]] ("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]], a group that is now recognized as a larger grouping including the orders [[Platydesmida]], [[Polyzoniida]], and [[Siphonophorida]].<ref name="Pocock1894" /> The following year, the American entomologist [[Orator F. Cook]] considered Stemiulids as "suborder Siphoniuloidea", closely related to [[Julida]]ns and [[Spirostreptida]]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.<ref>Hoffman RL. (1979) Classification of the Diplopoda. ''Geneve: Mus. Hist. Nat.'' 237 pp.</ref>{{efn|Gonopod morphology is one of the primary diagnostic traits in millipedes.}} With only two known species, Siphoniulida is the smallest order of millipedes, followed by [[Siphonocryptida]] with three to six species.<ref name=Breweretal2012>{{cite journal|last=Brewer|first=Michael S.|coauthors=Sierwald, Petra; Bond, Jason E.|title=Millipede Taxonomy after 250 Years: Classification and Taxonomic Practices in a Mega-Diverse yet Understudied Arthropod Group|journal=PLoS ONE|date=2012|volume=7|issue=5|pages=e37240|doi=10.1371/journal.pone.0037240}}</ref><ref name=Enghoff2010>{{cite journal|author=Enghoff, H.|year=2010|title= A new strikingly coloured species of ''Siphonocryptus'', sixth of its order (Diplopoda: Siphonocryptida)|journal=Zootaxa|volume=2681|pages= 66-68|url=http://www.mapress.com/zootaxa/2010/f/zt02681p068.pdf}}</ref>


In more recent years, millipedes have been studied by [[cladistic]] and modern [[phylogenetic]] methods, yet Siphoniulida remains engimatic. 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 [[Juliformia|juliform]] or colobognathan order".<ref name=Enghoff1984>{{cite journal|last=Enghoff|first=H.|title=Phylogeny of millipedes - a cladistic analysis|journal=Journal of Zoological Systematics and Evolutionary Research|date=1984|volume=22|issue=1|pages=8–26|doi=10.1111/j.1439-0469.1984.tb00559.x}}</ref> 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 (cladistics)|outgroup]] to all other helminthomorphs, and the internal classification of Helminthomorpha was significantly from Enghoff's.<ref name=Sierwaldetal2003/> In a subsequent study combining anatomical data with [[DNA sequence]] data from other groups, Siphoniulida again appeared as basal within Helminthomorpha.<ref name=Sierwald&Bond2007>{{cite journal|last=Sierwald|first=Petra|coauthors=Bond, Jason E.|title=Current Status of the Myriapod Class Diplopoda (Millipedes): Taxonomic Diversity and Phylogeny|journal=Annual Review of Entomology|date=2007|volume=52|issue=1|pages=401–420|doi=10.1146/annurev.ento.52.111805.090210}}</ref>
In more recent years, millipedes have been studied by [[cladistic]] and modern [[phylogenetic]] methods, yet Siphoniulida remains engimatic. 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 [[Juliformia|juliform]] or colobognathan order".<ref name=Enghoff1984>{{cite journal|last=Enghoff|first=H.|title=Phylogeny of millipedes - a cladistic analysis|journal=Journal of Zoological Systematics and Evolutionary Research|date=1984|volume=22|issue=1|pages=8–26|doi=10.1111/j.1439-0469.1984.tb00559.x}}</ref> 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 (cladistics)|outgroup]] to all other helminthomorphs, and the internal classification of Helminthomorpha was significantly from Enghoff's.<ref name=Sierwaldetal2003/> In a subsequent study combining anatomical data with [[DNA sequence]] data from other groups, Siphoniulida again appeared as basal within Helminthomorpha.<ref name=Sierwald&Bond2007>{{cite journal|last=Sierwald|first=Petra|coauthors=Bond, Jason E.|title=Current Status of the Myriapod Class Diplopoda (Millipedes): Taxonomic Diversity and Phylogeny|journal=Annual Review of Entomology|date=2007|volume=52|issue=1|pages=401–420|doi=10.1146/annurev.ento.52.111805.090210}}</ref>

Revision as of 21:11, 26 March 2014

Siphoniulus
Anterior and lateral views of head region
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Myriapoda
Class:
Diplopoda
Infraclass:
Helminthomorpha
Order:
Siphoniulida

Cook, 1895
Family:
Siphoniulidae

Pocock, 1894
Genus:
Siphoniulus

Pocock, 1894
Species

S. alba Pocock, 1894
S. neotropicus Hoffman, 1979

Siphoniulus is a poorly-known genus of millipede containing only two species: S. alba from Indonesia and S. neotropicus from Mexico and Guatemala. These two species are the only members of the family Siphoniulidae and order Siphoniulida, making Siphoniulida the smallest millipede order. Few specimens are known, and their classification is contentious, although most recent studies place them as basal members of the Helminthomorpha ("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 7.5 mm (0.30 in) long,[a] 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.[1][2] The exoskeleton is smooth and has few setae, and ozopores (defensive glands) are lacking. The third segment is legless. The single pair of gonopods in males consist of the anterior limbs on the seventh segment, and are partially recessed in the body. The telson (rear-most segment) possess small bristle-like structures called spinnerets.[1]

Distribution

S. alba is only known from a single specimen collected in 1894 near Maninjau on the Indonesian island of Sumatra. S. neotropicus was discovered near the Mayan ruins of Tikal in Guatemala, and is also known from the Mexican states of Chiapas and Veracruz.[1]

History

Siphoniulus alba (and the family Siphoniulidae) was described in 1894 by Reginald Innes Pocock, from a female specimen collected near Lake Maninjau on the island of Sumatra.[3] The specimen was deposited in the Zoological Museum Amsterdam, but by 1975 the specimen was missing its head and anterior segments.[2] S. neotropicus was described by Richard L. Hoffman in 1979 from two possibly immature females collected in Guatemala.[2] 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 revealed new specimens of S. neotropics, allowing for complete anatomical descriptions and characterization of the gonopods.[1]

Classification

Simplified cladogram from Sierwald et al 2003[1]

Polyxenida

Chilognatha
The incorporation of Siphoniulida anatomy did not clearly resolve relationships of millipede orders.
Simplified cladogram from Sierwald & Bond 2007[4]

Polyxenida

Chilognatha
Combining morphological with molecular data improved resolution, and also supported a basal helminthomorph placement of Siphoniulida.

Siphoniulids have been classified in various, conflicting placements within the Helminthomorpha ("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, a group that is now recognized as a larger grouping including the orders Platydesmida, Polyzoniida, and Siphonophorida.[3] The following year, the American entomologist Orator F. Cook considered Stemiulids as "suborder Siphoniuloidea", closely related to Julidans and Spirostreptidans (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.[5][b] With only two known species, Siphoniulida is the smallest order of millipedes, followed by Siphonocryptida with three to six species.[6][7]

In more recent years, millipedes have been studied by cladistic and modern phylogenetic methods, yet Siphoniulida remains engimatic. 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 or colobognathan order".[8] 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 to all other helminthomorphs, and the internal classification of Helminthomorpha was significantly from Enghoff's.[1] In a subsequent study combining anatomical data with DNA sequence data from other groups, Siphoniulida again appeared as basal within Helminthomorpha.[4]

References

  1. ^ The holotype and only known specimen of S. alba was described as 11 mm, but the anterior part of it is now missing.[1]
  2. ^ Gonopod morphology is one of the primary diagnostic traits in millipedes.
  1. ^ a b c d e f g Sierwald, P. (2003). "Millipede phylogeny revisited in the light of the enigmatic order Siphoniulida". Journal of Zoological Systematics and Evolutionary Research. 41 (2): 87–99. doi:10.1046/j.1439-0469.2003.00202.x. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ a b c Hoffman, R.L. (1979). "A siphoniulid milliped from Central America". Revue Suisse De Zoologie. 86: 535–540.
  3. ^ a b Pocock, R. I. (1894). "Chilopoda, Symphyla and Diplopoda from the Malay Archipelago". Zoologische Ergebnisse einer Reise in Niederlandisch Ost-Indien. 3: 307–404..
  4. ^ a b Sierwald, Petra (2007). "Current Status of the Myriapod Class Diplopoda (Millipedes): Taxonomic Diversity and Phylogeny". Annual Review of Entomology. 52 (1): 401–420. doi:10.1146/annurev.ento.52.111805.090210. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Hoffman RL. (1979) Classification of the Diplopoda. Geneve: Mus. Hist. Nat. 237 pp.
  6. ^ Brewer, Michael S. (2012). "Millipede Taxonomy after 250 Years: Classification and Taxonomic Practices in a Mega-Diverse yet Understudied Arthropod Group". PLoS ONE. 7 (5): e37240. doi:10.1371/journal.pone.0037240. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: unflagged free DOI (link)
  7. ^ Enghoff, H. (2010). "A new strikingly coloured species of Siphonocryptus, sixth of its order (Diplopoda: Siphonocryptida)" (PDF). Zootaxa. 2681: 66–68.
  8. ^ Enghoff, H. (1984). "Phylogeny of millipedes - a cladistic analysis". Journal of Zoological Systematics and Evolutionary Research. 22 (1): 8–26. doi:10.1111/j.1439-0469.1984.tb00559.x.
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