The name “millipede” translates lớn a thousvà feet (from mille “thousand” và pes “foot”). However, no millipede has ever been described with more than 750 legs. We discovered a new record-setting species of millipede with 1,306 legs, Eumillipes persephone, from Western nước Australia. This diminutive animal (0.95 milimet wide, 95.7 mm long) has 330 segments, a cone-shaped head with enormous antennae, and a beak for feeding. A distant relative sầu of the previous record holder, Illacme plenipes from California, it belongs khổng lồ a different order, the Polyzoniidomain authority. Discovered 60 m below ground in a drill hole created for mineral exploration, E. persephone possesses troglomorphic features; it lacks eyes and pigmentation, và it has a greatly elongated body—features that stvà in stark contrast to its closest surface-dwelling relatives in nước Australia và all other members of its order. Using phylogenomics, we found that super-elongation (> 180 segments) evolved repeatedly in the millipede class Diplopoda. The striking morphological similarity between E. persephone & I. plenipes is a result of convergent evolution, probably for locomotion in similar soil habitats. Discovered in the resource-rich Goldfields-Esperance region & threatened by encroaching surface mining, documentation of this species & conservation of its habitat are of critical importance.

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Among muốn the earliest animals khổng lồ breathe atmospheric oxygen1 và with some extinct species that grew lớn two meters in length2, millipedes have lived on this planet for more than 400 million years. Important as decomposers in terrestrial ecosystems3, primary knowledge of millipede diversity lags tremendously behind other animal groups. With fossil taxa dated to lớn the Cretaceous4,5, the millipede order Polyzoniida includes ca. 70 species with a distribution on all continents except Antarctica. Some of its members exhibit parental care of eggs6, others ooze chemical defenses containing alkaloids7 that are sequestered by poison frogs8,9, và some species roll into a ball for protection10. Hatchlings emerge from the egg with four pairs of legs, & continuously add segments during development for an indeterminate period of time, even after adulthood11. Polyzoniidans have sầu never before been observed in deep soil habitats, và most occur in surficial microhabitats of decaying wood và other detritus. Previously known Australian polyzoniidans have sầu at most 400 legs, eyes with 1–3 ommatidia, most with at least some dark pigmentation, a flat wide body (relative sầu to lớn others in the order), & occurrence in epigean microhabitats12. However, distantly related millipedes, such as Illacme species & other members of the family Siphonorhinidae (order Siphonophorida), have been recorded from as deep as 11.5 m below the soil surface13,14. These species possess a suite of adaptations, such as a thin elongated body with up to lớn 750 legs, no eyes, massive antennae, và lachồng of pigmentation. No siphonorhinid species have been recorded from Australia, & the geographically closest siphonorhinids occur in Madagasoto and Indonesia13,14.

Here we report the discovery of E. persephone, the first super-elongated millipede known from nước Australia, and the new world record holder of the animal with greachạy thử number of legs. It belongs to the family Siphonotidae (order Polyzoniida), yet appears similar lớn super-elongated millipedes in the order Siphonophorida. Eumillipes persephone lives deep underground, and it was only discovered by surveying geological drill holes originally created for mineral exploration that provided access to lớn a cryptic và previously unexplored underground habitat.


In August 20đôi mươi, in the Goldfields region of Western Australia, we discovered a pale, thread-lượt thích millipede with 1,306 legs at a depth of 60 m in a drill hole created for mineral exploration (Fig. 1). In total, 56 4–81 m deep 150 mm-diameter drill holes located at a site 100 km WSW of Norseman, Western Australia (within the Great Western Woodlands) were sampled for millipedes & other subterranean fauna, according to techniques described in ref.16. These geological drill holes provided a portal to lớn access an interstitial habitat composed of banded iron formations & mafic volcanic rocks, which are known to lớn harbor troglophilic fauna16,17. Eight individuals of the new species were collected from troglofaumãng cầu traps at depths between 15–60 m from three drill holes (450 m apart), including five individuals from a trap phối at a depth of 60 m. Two juveniles were collected in April 2020 và another one in January 2021, always from troglofaumãng cầu traps, attesting khổng lồ the species’ true deep subterranean life.


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The leggiest animal on the planet, Eumillipes persephone, from Australia. (A) female with 330 segments & 1,306 legs (paratype specimen, T147124). (B) ventral view of legs (male holotype, T147101). (C) dorsal view of head và ventral view of gonopods (male holotype, T147101). Scale bars, 0.5 mm.


The specimens superficially appeared khổng lồ be members of the Siphonorhinidae, due to phenotypic similarity to lớn Illacme plenipes Cook & Loomis, 1928. We used scanning electron microscopy & genome sequencing to lớn conclude that the remarkable anatomical similarity between E. persephone & I. plenipes is a result of convergent evolution of super-elongation (> 180 segments), which we here reveal that has originated at least twice in the millipede class Diplopoda (Fig. 2). Eumillipes persephone appears unlượt thích any other species in the order Polyzoniidomain authority. Its highly elongated and narrowed body, lack of eyes, massive antennae, shortened legs, and laông chồng of pigmentation comprise a suite of characters consistent with a fossorial bauplan that has repeatedly evolved in the Diplopoda18,19.


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Phylogenomic estimation of the evolutionary history of colobognath millipedes. Super-elongation (> 180 segments) is well known from the order Siphonophoridomain authority, including Illacme plenipes with 192 segments và 750 legs, but it has independently evolved in the Australian order Polyzoniidomain authority with Eumillipes persephone bearing up lớn 1,306 legs & 330 segments. This feature (dark branches) has evolved between two & four times in diplopods based on a character state reconstruction using parsimony. Maximum likelihood phylogeny of 312 orthologous sequences with Polydesmidomain authority, Stemmiulidomain authority, Chordeumatidomain authority, Spirostreptidomain authority, & Sphaerotheriidomain authority as outgroup taxa. Julida, Spirobolida, and other diplopod orders omitted from the analysis. Support values on nodes are bootstrap supports. Numbers in parentheses after species names are the maximum segment count for the taxon. Species with super-elongation present denoted in bold. Millipede silhouettes sized relative sầu to lớn one other. Diagram created with Adobe Illustrator 2021 (adobe.com/products/illustrator.html).


Taxonomy section

Class Diplopoda de Blainville in Gervais, 1844

Subterclass Colobognatha Brandt, 1834

Order Polyzoniida Cook, 1895

Family Siphonotidae Cook, 1895

Tribe Rhinotini Hoffman, 1977

Eumillipes, Marek new genus

http://zoongân hàng.org/NomenclaturalActs/a258f64e-0d4c-4941-be20-0b5d78e1078e.

Type species

Eumillipes persephone Marek, new species.

Generic placement and diagnosis

The genus Eumillipes is placed in the order Polyzoniida, family Siphonotidae, tribe Rhinotini based on the following characters10,20; whether the character is diagnostic for the order (O), family (F), or tribe (T) is denoted in parentheses. Head capsule small, conical, elongated into lớn a sharp snout (O) (Fig. 1C, Supplementary Fig. S1A–C). Prozonites & metazonites of trunk rings the same width (O) (Supplementary Fig. S2A); prozonites not narrow as in the Siphonophoridomain authority. Rings smooth (Supplementary Fig. S2B), covered with neither cuticular ornaments nor long setae as in the Siphonophoridomain authority. Vertex of head with two macrosetae (O) (Supplementary Fig. S1C). Antennae thichồng with equally sized antennomeres (O) (Fig. 1C, Supplementary Fig. S3A); antennae not strongly elbowed between antennomeres 3, 4 as in the Siphonorhinidae (Siphonophorida). Gnathochilarium reduced to lớn three sclerites: mentum; left, right stipes (O). Ozopores located far in from lateral edges of tergites; placed two-thirds the distance from midline laterally khổng lồ tergal margins (F) (Supplementary Fig. S2D). Vasa deferentia open through small conical lobes (penes) on the posterior surfaces of the second leg coxae (F). Telson a complete ring around the anal valves (F) (Supplementary Fig. S2D). Tarsal claw with long sigmoid-shaped accessory claw at its base that exceeds the claw in length (F) (Supplementary Fig. S1D). The genus differs from other siphonotid genera by the following characters. Anterior gonopods (i.e., 9th leg pair) strongly modified with podomeres 3–4 fused, not leg-like as in Siphonotini genera (T) (Fig. 1C, Supplementary figs. S4, S5A). Apex of anterior gonopods distinctly bifurcated into lớn two processes (Fig. 1C, Supplementary figs. S4, S5A), not a single process as in the genera Rhinotus Cook, 1896 and Siphonoconus Attems, 1930.

Eumillipes persephone Marek, new species

http://zoongân hàng.org/NomenclaturalActs/0AFB7037-E517-4D05-804B-D9AE1C7B3F47

Diagnosis

Adults of Eumillipes persephone can be differentiated from other polyzoniidan genera và species (and commonly encountered millipedes co-occurring with E. persephone in Western Australia) based on the combination of the following characters. Body extremely long and thread-like (width: ♂ 0.92 mm; ♀ 0.95 mm; length: ♂ 54.7 mm; ♀ 95.7 mm). Exoskeleton uniformly pale, cream-colored (Fig. 1A, Supplementary figs. S6–S8)—with neither dark pigmentation nor longitudinal, nor transverse stripes as in surface-dwelling species (Supplementary Fig. S9). Adult millipedes with an exceptional number of rings và legs: ♀ up khổng lồ 330 rings & 1,306 legs, and ♂ up to lớn 208 rings và 818 legs (Supplementary tab. S1). Head cone-shaped và eyeless (Fig. 1C, Supplementary Fig. S1A–C)—lacking eyes as are present in surface-dwelling species. Ninth và 10th leg pairs modified inlớn gonopods (Fig. 1C, Supplementary figs. S4, S5). Anterior gonopods (9th leg pair) highly modified, not leg like, và distinctly bifurcated into lớn two processes (Fig. 1C, Supplementary figs. S4, S5A). Medial process of the anterior gonopods saddle-shaped—not pointed & recurved as in Siphonotus flavomarginatus Attems, 191121. Lateral process sheath-like và cupping the medial process. Posterior gonopods (10th leg pair) stylet-lượt thích, và in repose threaded through the bifurcated anterior gonopods (Fig. 1C, Supplementary figs. S4, S5B). Stermãng cầu of gonopods with four long, slender, curved setae apically studded with spinules (Supplementary figs. S4B, S5A).

Material examined

Male holotype (WAM T147101), two female và one male paratypes (WAM T147100, T147124, T146684), & two juveniles (WAM T147122, T147123) from Western nước Australia, ca. 100 km WSW of Norseman, 32° 32′ 05.9" S, 120° 47′ 42.74" E, 27 May–4 August 2020, collected by A.J. Mittra and L.P.. Masarei (Western Australian Museum).

Variation

Males have sầu fewer segments & legs; specimen T147101 has 198 segments and 778 legs (Supplementary Fig. S7), and T147100 has 208 segments & 818 legs (Supplementary Fig. S8). Female specimen T147124 possesses 330 segments and 1,306 legs (Fig. 1A, Supplementary Fig. S6), and T146684 has 253 segments and 998 legs.

Etymology

The genus is named because it is the first true millipede with more than 1000 legs. The name Eumillipes is a combination of the Greek eu-, meaning ‘true’; Latin mille, ‘thousand’; and Latin pes, ‘foot’. It is to be treated as a noun. The species epithet is derived from the Greek mythological goddess of the underworld, Persephone, who was originally from the surface but was taken lớn the underworld by Hades.


From studies by Manton22 and đoạn phim footage of siphonorhinid millipedes, the locomotive sầu biomechanics of super-elongated millipedes has only been studied rudimentarily. Navigating by its enlarged antennae (Fig. 1C, Supplementary Fig. S3A, B) equipped with up lớn five sầu sensillum types15, the millipede’s elongated trunk with telescopic segments facilitates burrowing in a three-dimensional soil matrix. Its antennae wave sầu independently khổng lồ locate an opening; once a suitable gap is identified, the millipede enters and walks through. The flexible segments are compressible khổng lồ squeeze through narrow fissures. The continuous metachronal gait và musculoskeletal action of the segments, which are composed of concentric tubular rings that slide within one another, provide continuous pushing force; in combination with the legs, longitudinal (Supplementary Fig. S10C) & oblique muscles pull the rings together & provide forward locomotion22. This way of burrowing resembles that used by geophilomorph centipedes (another group of greatly elongated myriapods that includes the leggiest centipede, Gonibregmatus plurimipes Chamberlin, 1920 from Fiji with 191 rings and 382 legs) và earthworms. In contrast with millipedes with incompressible rings such as “bulldozer” ecomorphs that walk in a single plane propelled by the additive sầu force of their legs22, colobognath millipedes are able to lớn wind their way through a three-dimensional matrix & can simultaneously walk in up lớn eight different planes. This telescoping locomotion, by sliding trunk segments (Supplementary Fig. S2A) coupled with the thrust of the legs, propels the animal through a varied & unpredictable underground microhabitat22, and the increase in leg number likely contributes more pushing power khổng lồ force through small crevices & openings. Super-elongation in the Diplopodomain authority has repeatedly evolved in taxa that live sầu in these microhabitats, such as in Siphonorhinidae (I. plenipes with 192 segments & Nematozonium filum Verhoeff, 1939 with 182 segments), Siphonophoridae (Siphonophora millepedomain authority Loomis, 1934 & Siphonacme lyttoni Cook & Loomis, 1928 each with 190 segments), và E. persephone. Each additional ring provides extra locomotory thrust23, and E. persephone’s up to 330 rings may be specially adapted lớn locomotion in its comparatively deep soil microhabitat at 60 m—five-fold greater than the maximum depth of Illacme species. Trunk super-elongation may also serve khổng lồ lengthen the digestive canal to lớn increase the absorptive surface area & assimilation efficiency in a resource-limited subterranean habitat, as may be the case for I. plenipes, which additionally has an even longer corkscrew-shaped gut than the trunk itself15. The diet of E. persephone is unknown, but may be similar khổng lồ other primarily fungivorous colobognath millipedes, such as the platydesmidan Brachycybe lecontii Wood, 1864 that feeds on up to 176 different genera of fungi24.

Current alpha-màn chơi knowledge of Australian Siphonotidae is fragmentary. Although an unpublished dissertation from 1994 documented eight genera & 42 species of the family25, taxonomy of the group remains antiquated with two genera và five species currently listed from the continent described about a century ago21,25,26. Although the phenotypic divergence of E. persephone from surface-dwelling family relatives appears to be associated with adaptations khổng lồ life underground, extraordinary similarity of its gonopods (species-diagnostic features in diplopods) with Siphonotus flavomarginatus from Torbay, Western Australia, indicates a genus-cấp độ affiliation. Cthua thảm similarity of gonopod anatomy with extremely divergent somatic features suggests rapid evolution of troglomorphic traits.

Invertebrates that live sầu below the Earth’s surface comprise a cryptic and diverse fauna. Although they are challenging lớn observe sầu & document, notable recent discoveries include beetles & millipedes in Brazilian iron ore caves27,28, snake millipedes of mesovoid shallow substratum of Spain29, and spiders from caves of the Edwards Plateau of Texas30. These habitats are repositories of incredibly rich, but obscure biodiversity. These underground habitats, and their inhabitants, are critically understudied, despite their ecological importance in filtration of groundwater và screening of environmental toxins. The subterranean conditions of Western Australia may consistently be at a much lower temperature and higher humidity and house an evolutionarily closely related mesic-adapted troglofaumãng cầu. Despite surface temperatures in excess of 46 °C và less than 300 mm/year of precipitation31, the groundwater in the sites where E. persephone was collected never exceeded 22 °C. Surface climatic conditions fluctuated considerably across hundreds of millennia, but underground conditions probably remained comparatively stable. Troglophilic species often represent ancient vestiges of formerly widespread lineages that now persist in subterranean refugia32. Although the date of the split between the clade containing E. persephone và the one containing Siphonotus flavomarginatus is uncertain, divergence may be linked khổng lồ aridification of the continent between 15–1.75 Ma. The so-called “climatic relict” theory has been useful to explain other such close relationships between troglophilic và epigean taxa, such as springtails, isopods, schizomids, pseudoscorpions, và ground beetles in Western Australia17,33. This theory suggests that cool-adapted epigean ancestors were gradually driven underground where conditions remained favorable, whilst the surface dried & became uninhabitable; following aridification, epigean lineages underwent extinction thereby fostering allopatric speciation33. A similar theory has been invoked for faunal radiations in caves, where analogous extreme adaptive sầu shifts also occur accompanied by morphological change: eyelessness, elaboration of mechanical sensation, lack of pigmentation, và leg elongation. Elongated limbs in troglobionts have been hypothesized to have originated for more efficiently traversing expansive cavernous space for scarce food và mates34. In the case of E. persephone, và its micro-cavernous habitat, the remarkable number of legs may be associated with a comparable search for limited resources in its “micro-cave”-like interstitial habitat. Short legs are likely advantageous in the small cavities of such a habitat, and perhaps compensated for by an increase in their number, which would maintain pushing power.

Located in the Yilgarn Craton, the Eastern Goldfields Province of Western nước Australia composes a surficial habitat of shrublands (Supplementary Fig. S11) overlaying an ancient terrane that is aước ao the oldest emergent lvà masses (2.6–4.4 billion years, ref.35). A large quantity of Australia’s gold, nickel, & other minerals are extracted from the Goldfields, và intensive sầu surface mining has occurred in the area for more than a century. Mineral exploration includes surveying underground via millions of drill holes that produced cores for elemental analysis in the region. These holes, which are later rehabilitated, provide fleeting access to sample an expansive sầu vadose zone which houses a subterranean biodiversity hotspot17,36.

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Whether troglomorphic species of Eumillipes exist in other parts of Western Australia is an uncertain, but potentially rich avenue of discovery. The unexpected discovery of E. persephone và other troglomorphic animals from the Great Western Woodlands37,38, within the Eastern Goldfields Province of Western Australia, highlights the region as an exceptional repository of biodiversity.