Research Article |
Corresponding author: Leonardo D. Fernández ( limnoleo@gmail.com ) Academic editor: Pavel Stoev
© 2024 Antonio Parra-Gómez, Jorge Pérez-Schultheiss, Leonardo D. Fernández.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Parra-Gómez A, Pérez-Schultheiss J, Fernández LD (2024) Redescription of the enigmatic myriapod Hanseniella chilensis (Hansen, 1903) (Symphyla, Scutigerellidae) based on scanning electron microscope images of Chilean specimens. ZooKeys 1198: 1-15. https://doi.org/10.3897/zookeys.1198.119723
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Hanseniella chilensis is the only myriapod of the class Symphyla known from Chile. This garden centipede, or pseudocentipede, was described more than 120 years ago based on morphologically incomplete specimens collected in central Chile, a well-known biodiversity hotspot. In this study, we redescribe this species based on morphologically complete specimens collected near the type locality using scanning electron microscope images. Our study provides the description of diagnostic characters hitherto unknown in this species such as macrochaetae of the tergites and spinnerets of the cerci. We also include a new record from central Chile and discuss the presumed presence of this species in Argentina and Madagascar.
Biodiversity hotspot, biogeography, Chile, garden centipede, Myriapoda, pseudocentipede, SEM images, soil-dwelling arthropod, symphylans, taxonomy
Symphylans, also known as garden centipedes or pseudocentipedes, are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda. Symphylans are among the least studied soil microarthropods in the world. Often, the identity and geographic distribution of these myriapods are uncertain because they are relatively small and so difficult to study that many researchers simply overlook them (
In the Neotropical region, symphylans are represented by 21 species distributed across six genera and two families (
Chilean symphylans are among the least known in the Neotropical region (
Later,
To date, it is unknown whether the symphylans recorded in Madagascar and Argentina belonged to H. chilensis or to other similar yet undescribed species. Unfortunately, Hansen’s original description of H. chilensis was based on individuals that lacked key morphological traits for identification and diagnosis of symphylans, such as most macrochaetae of the tergites and spinnerets of the cerci (
In this study, we redescribe H. chilensis based on scanning electron microscope images of morphologically complete specimens collected in central Chile. Additionally, we report a new record in Chile and discuss the presumed presence of this species in Madagascar and Argentina.
Specimens of H. chilensis included in this study were collected between 2022 and 2023 in the rural locality of Lefuco, near Temuco city, La Araucanía region, central Chile. This reference is important because some of the specimens used by Hansen to describe H. chilensis came from the surroundings of this city (
Once in the laboratory, specimens were deposited in Petri dishes with 95% ethanol or mounted on concave microscope slides filled with glycerol and examined under dissecting and light microscopes, respectively. Morphological features were measured using IMAGEJ v. 1.53u software (
Specimens coded as APG-17-a and PG-71-L-a (field code, see results) were photographed under the scanning electron microscope (SEM). SEM specimens were mounted on stubs and then dehydrated using a Hitachi HCP-2 critical point dryer. Afterwards, specimens were coated with gold and palladium on a Leica EM ACE200 and photographed with a Zeiss EVO M10 SEM operating at 20 kV. The SEM photographs were processed in GIMP v. 2.10.32 software, and FIGUREJ plugin for IMAGEJ (
The investigated specimens were deposited at the Museo Nacional de Historia Natural de Chile (National Museum of Natural History of Chile,
Subphylum Myriapoda Latreille, 1797
Class Symphyla Ryder, 1880
Family Scutigerellidae Bagnall, 1913
Genus Hanseniella Bagnall, 1913
Scolopendrella immaculata
Scutigerella chilensis
Hansen, 1903: 27, 32, 46, 48, 51, plate 4, figs 4a–g;
Hanseniella (Hanseniella) chilensis
Hanseniella chilensis
Types not designated by
2 males, Chile: La Araucanía region, Malleco province, Estero Lefuco, under rotting wood chips, -38.5153, -71.7273, 15-I-2022, APG14 (field code); 1 male, same locality, leaf litter, -38.5135, -71.7263, 31-I-2022, APG17-a (field code); 1 male, 2 female, same locality, under a rotting log ca. 944 m a.s.l., -38.5132, -71.7275, 19-IX-2023, PG-71-L/PG-71-L-a (field code).
Adults specimens of Hanseniella chilensis can be separated from related species by the following combination of characters: Central rod follow by a triangular sulcus with a distinct small anterior seta, and two posterior setae (Figs
Chaetotaxy and posterior margin shape of the tergites, except the rudimentary first tergite.
Tergite number | Number of setae on tergal surface and margins (ca.) | Number of rows (counting hind setae as so) | Anterolateral macrochaeta (per side) | Posterolateral macrochaeta (per side) | Hind macrochaeta pointing outwards and/or forwards (per side) | Posterior margin |
---|---|---|---|---|---|---|
2 | 33–38 | 3 | 1 | 1 | 1 | Almost straight |
3 | 41–55 | 3 | 1 | 1 | 1 | Almost straight |
4 | 42–52 | 3 | 0 | 1 | 1 | Almost straight |
5 | 37–47 | 3 | 0 | 1 | 1 | Almost straight |
6 | 61–82 | 5 | 1 | 1 | 1 | Almost straight |
7 | 56–65 | 3 | 0 | 1 | 1 | Slightly concave |
8 | 38–55 | 3 | 0 | 1 | 1 | Slightly concave |
9 | 67–82 | 5 | 1 | 1 | 1 | Almost straight |
10 | 57–65 | 3 | 0 | 1 | 1 | Slightly concave |
11 | 44–59 | 3 | 0 | 1 | 1 | Slightly concave |
12 | 66–84 | 5 | 1 | 1 | 1 | Almost straight |
13 | 54–65 | 3 | 0 | 1 | 1 | Slightly concave |
14 | 61–71 | 5 | 0 | 1 | 1 | Slightly concave |
15 | 33–46 | 2–3 | 0 | 0 | 1 | Convex between cerci |
APG-17-a Male, dorsal view A head, first tergite and part of the second tergite (dfs-distinct frontal seta, ms-macroseta) B tergites 2–5 (am-anterolateral macrochaeta, hm-hind macrochaeta, pm-posterolateral macrochaeta) C tergites 11–13 D last tergite and cerci (hm-hind macrochaeta (abraded), hs-hind seta). Scale bars: 200.0 µm (A–C); 100.0 µm (D).
Details of some relevant structures of APG-17-a Male (A, B) and PG-71-L-a Female (C, D) A central rod and triangular sulcus from the top of the head (hs-hind seta, oe-ovoid end, ss-short seta, ts-triangular sulcus) B tergal surface of tergite 3 (cr-cuticular rim) C Tömösváry organ and proximal surface (km-knob with microseta, lp-linguiform protuberance) D apical zone of the last antennomere (sb-sensilla basiconica, so-sensory organ). Scale bars: 50.0 µm (A, B); 10.0 µm (C, D).
Length of body (measured dorsally) without cerci and antennae: female ca. 3.5–4.3 mm, males ca. 4.7–5.2 mm. Head. 1.4 times broader than long, frontal margin slightly convex with 1+1 distinct setae, lateral margins convex with a sharp anterolateral angle, posterior margin concave with rounded posterolateral angles (Fig.
PG-71-L-a Female, ventral view A head and first pair of legs B ventral surface details proximal to left leg of pair 8 and its 2 first podomeres, podomere 4 and 5 of pair 7 partially show (lm-laminar needles, sc-scale-like cuticle, slm-“scales” with laminar needles) C coxal sac near leg pair 4 D last pair of legs and cerci (ap-apical seta, ls-large seta, os-outer seta). Scale bars: 100.0 µm (A, D); 50.0 µm (B); 20.0 µm (C).
Illustrations showing some relevant structures of the species A antennomere 20 of a male B apical antennomere (sensory organs not as detailed as described due to their small size, smallest one not visible on this angle) C distal end of the first pair of legs D distal end of the last pair of legs (frontal seta abraded) E styli. Scale bar: 50 µm.
Africa: ?Madagascar: Banks of Betaly River, near Bezavona (see Remarks); South America: Argentina: Neuquén Province: Lago Curruhué (Currhue mendum
Direction of macrochaetae can be variable due to specimen conservation and preparation on slides, but on live specimens in the field, the macrochaetae seem to point forwards in most, if not all, tergites (Fig.
Investigation of complete specimens of H. chilensis collected in central Chile allowed us to conclude that this species shares important morphological similarities with only one other congeneric species. Particularly, we noted that H. chilensis exhibits macrochaetae on all tergites (excluding the rudimentary first), a trait shared only with H. capensis (
Additionally,
Unfortunately, we were unable to compare H. chilensis with H. hardyi (Chamberlin, 1920), H. neozelandica (Chamberlin, 1920) and H. paolettii Scheller, 1993 because the number of macrochaetae present in their tergites remains unknown (
Hanseniella chilensis is a symphylan species described by
After being described in Chile, H. chilensis was recorded in Madagascar (
The latter scenario is plausible because Chile is surrounded by biogeographic barriers that limit species dispersal, including the Atacama Desert in the north, the Andes Mountains in the east, the Pacific Ocean in the west, and the Drake Passage to the south (
Alternatively, H. chilensis could be a truly ubiquitous species, which has managed to establish viable populations in different countries. The means of dispersal of symphylans remains unknown, but we can assume that they could overcome biogeographic barriers by passive dispersal. Airborne dispersal is used by some arthropods, but symphylans are unlikely to use this method. They are soil-dwelling and apparently do not have morpho-physiological adaptations to balloon-like spiders or to resist desiccation and UV radiation for long periods of time. Phoretic dispersal seems more plausible since symphylans could overcome biogeographic barriers by being transported on the fur of mammals or feathers of migratory birds. They could also colonize islands by floating on objects such as driftwood. Accidental introduction might be another plausible means of passive dispersal. There is currently an active trade in raw materials and products of plant origin among Chile, Madagascar and Argentina (
The ecology of H. chilensis is unknown, so we are unaware of the consequences that the introduction of this species into exotic ecosystems could have. For example, the symphylan Scutigerella immaculata has been accidentally introduced in several countries and now is considered an agricultural pest (
The information provided in our study could contribute to resolving the geographic range of H. chilensis, including its status as an endemic or ubiquitous species. We have redescribed H. chilensis in detail: we provided SEM images as well as drawings and descriptions of diagnostic characters that were previously unknown in this species. Therefore, it is now possible to investigate whether the putative specimens of H. chilensis from Madagascar and Argentina belong to the same species. The resolution of this long-standing question would not only improve our understanding of Symphyla diversity, but also provide indirect information on the dispersal strategies and dispersal ability of these arthropods.
We are indebted to our colleague Jackson Means and copy editors Christopher Glasby and Polina Petrakieva who kindly reviewed the English writing of our study. We thank Pavel Stoev, Yun Bun and Miguel Dominguez Camacho for reviewing and contributing to significantly improving our study. We also thank Freddy Ruiz, Diego Salazar and the Florentino Ameghino Library for providing part of the literature used in this study. Finally, we thank the kind assistance of Dagoberto Boisier and the team of the Electron Microscopy Unit, a core facility – Zeiss Reference Center of Universidad Austral de Chile for taking the SEM images used in this study.
The authors have declared that no competing interests exist.
No ethical statement was reported.
This study was funded by the ANID FONDECYT REGULAR 1220605 project awarded to L.D. Fernández.
Conceptualization: APG. Funding acquisition: LDF. Methodology: APG, JPS. Resources: LDF. Writing – original draft: LDF, APG.
Antonio Parra-Gómez https://orcid.org/0000-0002-4144-6610
Jorge Pérez-Schultheiss https://orcid.org/0000-0003-4537-5677
Leonardo D. Fernández https://orcid.org/0000-0001-9550-1921
All of the data that support the findings of this study are available in the main text.