Pauropoda

Pauropods are small terrestrial Myriapods that look like centipedes but are believed to be a sister group to millipedes. There are over 700 species of pauropods worldwide and they are classified into two different orders: Hexamerocerata and Tetramerocerata [1]. Fossils of pauropods have only been found from the time of Baltic Amber onward. No reliable internal phylogenies for pauropoda have been proposed due to the group being taxonomically understudied and its total worldwide fauna is estimated to be around 5000 species [3] [1].

A sclerotised pauropod in the new discovered family Eirmopauropodidae found on Stewart Island, New Zealand. This family only has one species on record.

Phylogeny

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Myriapoda

Class: Pauropoda

Hexamerocerata

Hexamercocerata strongly telescopic antennal stalk, a 12-segmented trunk, and 11 pairs of legs. Most members of this group are long, larger than other groups, and normally white [2]. This order contains only one family, Millotauropodidae, which is comprised of a single genus, Millotauropus [7].

Tetramerocerata

Tetramaerocerata have 4-segments and have scarcely telescopic antennal stalk, 6 tergites, and 8-10 pairs of legs. Most members of this order are small and white or brown. Most of the species in this order have 9 pairs of legs when they become adults. The order consists of 3 superfamilies containing 8 families: Pauropodoidae (Peaureopodidae, Polypauropodidae, Amphipauropodidae and Diplopauropodidae), Brachypauropodoidae (Brachypauropodidae and Hansenauropodidae), and Eurypauropodoidea (Eurypauropodidae and Sphaeropauropodidae) [7].

A comparison of morphologies between extant myriapoda. A: Scutigerella immaculata, a symphylan; B: a pauropoda; C: Otocryptops sexspinosa, a scolopendromorph centipede; D: a polydesmoid millipede.(Snodgrass 1952)

Anatomy

Pauropods are small (0.5-2.0 mm) terrestrial myriapods with a flexible trunk, and have 8-11 pairs of legs [4]. Most do not have a respiratory system, the exception being in Hexamerocerata which posses a single pair of trachea connected to spiracles on the coxae of the first leg pair [6]. Most Their head is small and directed downwards, and has no eyes. Instead, they use sensory organs found on their antennae. Their most distinctive feature is their branched antennae. One of the branches is their sensory organ (globulus), a second branch is the pseudoculi, which is an eye like structure, and the third branch there is the trichobothria, which is used to detect airborne vibrations and currents [2]. They have mouthparts similar to millipedes but may be reduced for the adaptation for suction of fluids [6]. Behind their last segment is their anal segment, called the pygidium, and this segment is horizontally divided. Due to its structure, this plate is used for identification. Each species can be identified by this, even at larvae stages [2].

Habitat, Diet, and Collection Methods

Pauropods can be found moist subterranean areas such as under stones, decaying plant matter, and moss beds. They can be found primarily 10-20 centimeters deep in soils but can go deeper by following root canals and crevices and go no deeper than the groundwater surface [2].Hexamerocerata are found strictly in tropical habitats while Tetramerocerata are have a sub-cosmopolitan distribution. For most species little is known about their eating habits, but mosy feed on fungal hyphae and spores. All tetramerocate pauropods used their reduced mouthparts use a suctorial method of feeding to consume fungi and semiliquid decaying plant matter. Millitauropus (an Hexamerocerata) is known to feed on springtails and their eggs [6]. There is also at least one species that can eat root hairs [2]. The most common way to collect pauropods is by using Berlese (Tullgren) Funnels.

Behavior

Pauropods have a patchy occurrence and can often be found on the underside of stone and tree branches. They are swift runners with mouse-like intermittent rushes and most species can turn its body almost 180°. Shy of light they try to stay hidden in crevices and in soil clumps. To examine the environment there antenna constantly rotate with high rapidity. The sexes are separate and the males drop there sperm in spherical packets which the females will seek out and pick up. Vertical migration occurs when there is changes in soil moisture levels.

An adult and first instar of the eurypauropod Trchypauropus britannicus. As the instar molts and grows, new segments and legs will be added.

Reproduction

Pauropods are hermaphroditic and progoneate, meaning that their genital opening is placed near the anterior part of their body. In unfavorable environments parthenogenetic reproduction can sometimes occur. Their eggs are developed in a short pupoid stage before the first larval instar appears [2]. This first post embryonic stage does not move and processes unarticulated traces that later develop into antennae as well as the first two pairs of legs. Like other myriapods they undergo the process of anamorphosis which allows for the addition of new segments and legs through growth and molting [6]. In Hexaerocerata the first larval instar has six pairs of legs. In Tetramerocerata the first larval instar has three pairs of legs, then is followed by instars of five, six, and eight pairs of legs. Adults will have eight, nine, or ten pairs of legs [2].

References

1. Andrew Austin, E. F.-J., s Mark Harvey, Mike Hodda, John Jennings, Claire Stephens, Erich Volschenk, David Yates. Key to Australian Freshwater and Terrestrial Invertebrates. https://keys.lucidcentral.org/keys/v3/TFI/start%20key/key/myriapoda%20key/Media/HTML/Pauropoda.html
2. Scheller, U. 2004. Pauropoda (Pauropods). Pages 375-377 in M. Hutchins, R. W. Garrison, V. Geist, P. V. Loiselle, N. Schlager, M. C. McDade, D. Olendorf, A. V. Evans, J. A. Jackson, D. G. Kleiman, J. B. Murphy, D. A. Thoney, W. J. Bock, S. F. Craig, and W. E. Duellman, editors. Grzimek's Animal Life Encyclopedia. Gale, Detroit, MI. http://link.galegroup.com/apps/doc/CX3406700133/GVRL?u=sunybuff_main&sid=GVRL&xid=a1db1709
3. Shear, W. A., and G. D. Edgecombe. 2010. The geological record and phylogeny of the Myriapoda. Arthropod Structure & Development 39:174-190. http://www.sciencedirect.com/science/article/pii/S1467803909000887
4. David Coleman, M. C., D. Crossley, Jr. 2017. Fundamentals of Soil Ecology. Third edition. Candice Janco, Academic Press.
5. Tree of Life Web Project. 2002. Pauropoda. pauropods. Version 01 January 2002 (temporary). http://tolweb.org/Pauropoda/2531/2002.01.01 in The Tree of Life Web Project, http://tolweb.org/
6. Encyclopedia of Biodiversity, Elsevier Science & Technology, 2013. ProQuest Ebook Central, https://ebookcentral-proquest-com.gate.lib.buffalo.edu/lib/buffalo/detail.action?docID=1130081.
7. Scheller, U. (2008). A reclassification of the Pauropoda (Myriapoda). International Journal of Myriapodology, 1(1), 1–38. https://doi.org/10.1163/187525408X316730