Pauropoda Lubbock, 1867

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Suggested Common Name: Pauropods
Number of subordinate taxa: around 1000 described species globally in 2 orders and 13 families, over 140 species in 2 orders and 8 families currently known from our area. The 5 families not represented in our area are all known from a single genus or species.
Etymology: παῦρος (paûros) [Ancient Greek] = few + poda [New Latin] =  feet, referring to the small number of legs in adults compared to other Myriapoda known at the time.
Taxonomic History: [incomplete]
Size Range: ranging from less than half a millimeter to just barely exceeding two.
Description: [incomplete]
Type taxon: [incomplete]
Notes: Despite already containing around a tenth of the world's described fauna, North America is severely undersampled for pauropods in terms of geographical and ecological coverage, problematic when the group displays high rates of endemism and often very small or fragmented ranges. Worsening the issue, early research into the species of our region often proves to be entirely unusuable or cripplingly confused in a modern context, nullifying the usefulness of nearly anything written on the subject before the mid-20th century and forcing modern workers to confine numerous names to the realm of incertae sedis or nomen dubium. This is even further compounded by a lack of understanding of the anatomy of the animals, poor documentation of otherwise taxonomically useful morphological features, and a frustratingly plastic degree of morphological stability between taxa. As a result identification of material can be difficult and problematic, and our current knowledge of pauropod diversity both in North America and globally has severe and obvious paucities.
Unsurprisingly, not much can be said for certain about the distributional patterns, biogeographical history, or even ecology of the mast majority of North American pauropod fauna. While only 2 recognizable species are known from the entirety of Mexico, Jamaica alone has over 15 known species and an endemic genus. Such disparities reflect extremely sporadic sampling efforts and a lack of attention given to unidentified collection material, and call for more thorough efforts to understand this highly interesting and species rich group. However, some general trends can still be given based on the data that has been gathered in more well sampled regions.
Some of our species are highly cosmopolitan with a nearly worldwide but sporadic distribution, likely reflecting a historied transport through commerce and agriculture; it can be presumed that none of these are native, although their true origins may be unclear. In a similar vein, North America also has unusual records of uncommon species that are known only from localities quite distant from one another, sometimes even differing drastically in climate and habitat; an example would be Decapauropus lambertoni, a species known only from islands in the Indian Ocean, several areas in Argentina, and a suburban roadside in California, whose apparent closest relative D. remigatus is known from a single specimen collected from an Ontario farm. In both of these patterns, the predominant genus is Decapauropus, a hyperdiverse group likely prone to human transport due to its ubiquitous nature. Among species presumed to be native, the eastern third of the continent north of Mexico seems to be significantly less diverse than western parts, containing fewer species overall and with many of them widespread. However, the few studies that have been conducted in more undisturbed environments of this region have yielded a surprisingly large array of more localized species, suggesting that this part of North America or certain environments in it were once home to a very species rich community of pauropods that has been largely displaced by human development. The midwest is unfortunately both poorly sampled and poorly understood. The western third has revealed the highest concentration of native species, with many unique radiations and numerous endemics, many only known from small areas. Even higher diversity can be expected in continental North America south of the US, but as previously stated studies of the region are nearly nonexistent. While only a few islands have been sampled in the Caribbean, the species diversity documented is very high and endemism seems common in at least the Hansenauropodidae.
Biogeographically, the North American pauropod fauna presents a bit of a puzzle. While the ties between the western portions of the continent with Beringian portions of the Eastern Hemisphere and Japan, the southern regions with South America, and the eastern portions with the Palearctic seen among the North American pauropods are fairly standard, there is a confusing but clear tie between North American and Afrotropical pauropods. Many of our pauropods, particularly those in the eastern continental portion and the Caribbean, have their closest morphological analogues found in the Afrotropics, apparently without many intermediaries or close relatives in South America. Hansenauropus, for example, has only 3 species known from Panama, Sierra Leone, and strangely enough New Zealand. Eastern North America also presents a number of species apparently shared with the Afrotropics, but not known from elsewhere; whether this is a coincidence of introduction or not is unknown.

Key to families (provided by Grant Wang)
1 a. Body with 12 dorsally visible tergites and 10-11 leg pairs in the adult. Temporal organ free from surrounding head cuticle on all sides, cup or mushroom shaped. Apical differentiated antennal sensillum without an internal capsule --> Hexamerocerata 2
b. Body with 9-8 dorsally visible tergites and 8-10 leg pairs in the adult. Temporal organ largely fused to the surrounding head cuticle, amorphous sac with optional appendages. Apical differentiated antennal sensillum with an internal capsule --> Tetramerocerata 3

2 (1) a. Antennae 5 segmented, telescopic, apical differentiated sensillum without bracts. Majority of bodily setae normal, tergal head setae all similar. First pair of tracheae extensive, well developed. Pygidium sternum with 3 pairs of setae --> Millotauropodidae (Millotauropus, extremely rare)
b. Antennae 4 segmented, not telescopic, apical differentiated sensillum with bracts. Majority of bodily setae reduced and pin-shaped, tergal head setae of 2 types. First pair of tracheae reduced as others. Pygidium sternum with numerous pairs of setae --> Undescribed family (Undescribed genus, extremely rare)

3 (1) a. Body heavily sclerotized, with hard, well pigmented plates covering the entire body and hiding the head and pygidium in a dorsal aspect --> Eurypauropodidae (Eurypauropus)
b. Body variously sclerotized, but never with hard plates hiding the pygidium in a dorsal aspect, usually poorly pigmented --> 4

4 (3) a. Body with marked, distinctly sclerotized plates that often hide the head in a dorsal aspect, dorsoventrally flattened; movements sluggish and creeping when alive --> Brachypauropodoidea 5 (Uncommon)
b. Body at most very weakly sclerotized, with demarcations between segments often indistinct, cylindrical. Head always distinct in a dorsal aspect; movements fast and erratic when alive --> Pauropodoidea 6

5 (4) a.  Some tergites subdivided both transversely and longitudinally to form at least 4 sclerites --> Brachypauropodidae (Uncommon)
b. Subdivided tergites only split transversely, forming a protergite and metatergite --> Hansenauropodidae (Uncommon)

6 (4) a. Pygidium apparently without anal plate, instead with a pair of elongated cuticular appendages. Sternal antennal branch with two distinct globuli branching from a single basis --> Polypauropodidae
b. Pygidium with at least one anal plate. Sternal antennal branch with a single distinct globulus --> 7

7 (6) a. Pygidium with two anal plates, one on the tergum and one on the sternum. Temporal organ with  a well developed finger-like vesicular organ --> Diplopauropodidae  (Diplopauropus, extremely rare)
b. Pygidium with a single anal plate on the sternum, although a shelf like extension of the tergum may be present. Temporal organ very rarely with a vesicular organ  --> 8

8 (7) a.  Setae of body very short and strongly clavate; sternal antennal branch with two very short and strongly clavate setae --> Amphipauropodidae (Amphipauropus, extremely rare)
b. Setae of body rarely markedly differentiated; sternal antennal branch with a single usually undifferentiated seta --> Pauropodidae (Extremely common)

Sources

Scheller, U. (1984). Pauropoda (Myriapoda) of Canada. Canadian Journal of Zoology, 62: 2074-2091.

Scheller, U. (2008). A reclassification of the Pauropoda (Myriapoda). International Journal of Myriapodology, 1(1): 1-38.

Published: Apr 1, 2023