Phylogeny of Geophilomorpha (Chilopoda) inferred from new morphological and molecular evidence

A new species of the rare genus Endogeophilus from southern France, with a key to the European genera of Geophilidae s.l. (Chilopoda)

The geophilid centipede Endogeophilusalberti sp. nov. is described and illustrated based on a single specimen collected from Provence, southern France. It is very similar to E.ichnusae Bonato, Zapparoli, Drago & Minelli, 2016, which is known only from three specimens from south-western Sardinia, and was the only species in the genus Endogeophilus Bonato, Zapparoli, Drago & Minelli, 2016. Both species share a remarkably narrow body, very short setae, and an unusually high number of legs, which are relatively stout. All these traits are rare among geophilids and suggest an endogeic life style. Despite of the very few specimens available for comparison and the difficulties to distinguish inter-specific differences from intra-specific variation, the two species differ at least in the shape of the pretarsi of the second maxillae and the shape of the forcipules. A revised diagnosis of the genus Endogeophilus is also provided, with an identification key to all genera of Geophilidae s.l. recorded so far in Europe, based on selected characters to evaluate without anatomical dissection and illustrated with original pictures.

A comprehensive dataset of the geophilid centipedes of the south-eastern Alps (Chilopoda, Geophilomorpha, Geophilidae s.l.)

Background

Centipedes of the family Geophilidae s.l. are widespread in the Holarctic, with the south-eastern part of the European Alps standing out as one of the most investigated regions. However, retrieving the published records for this taxon, even for this region, is challenging, since most of them are sparse in the specialised literature and interpreting them is hampered by the many taxonomic and nomenclatorial changes occurred in the past and recent times.

New information

We assembled and released a dataset of occurrence records of the geophilid species in the south-eastern Alps, including all the published records and many other records present in unpublished catalogues of scientific collections. For each record, we integrated information from all the sources about: locality, date of collection, the taxonomic identifications, number and sex of individuals and available sequences of molecular markers. For all the records, we estimated geographic coordinates of the locality, when not originally provided, based on the information available. We also estimated the accuracy of the position.The dataset includes 3293 records referred to 39 species, obtained since the first half of the 19th century and up to 2022; 52% of these records have been released publicly for the first time in the dataset here described.

An updated synthesis of the Geophilomorpha (Chilopoda) of Asian Russia

A comprehensive overview of the state of knowledge on the ChilopodaGeophilomorpha of the Asian part of Russia is presented, based on the critical revision of all published morphological descriptions and all geographical records. Revised diagnoses for all the 38 nominal species so far reported from Asian Russia are given, with comments on their validity. Among them a total of 18 species are recorded only from this region and many of them from a single locality only. The species belong to Geophilidae s. l., (in the genera Arctogeophilus, Geophilus, Pachymerium, and Strigamia), Schendylidae (Escaryus), and Mecistocephalidae (Agnostrup, Arrup, and Tygarrup). At least two species have been introduced, namely Geophilusflavus and Tygarrupjavanicus. The history of studies on the Geophilomorpha in the Asian part of Russia are also summarized.

Soil centipedes (Chilopoda, Geophilomorpha) in the Val Camonica forests (Southern Alps): species composition and richness

Soil centipedes (Chilopoda, Geophilomorpha) are a widespread group of predators in the forest soils of the European Alps. While in the eastern and western parts of the Southern Prealps, larger efforts were devoted to sample and study the geophilomorph fauna, little is known about species richness and composition of geophilomorph communities in the central part of Southern Prealps. In this work, five sites located in the Val Camonica were surveyed by hand searching, between November 2021 and July 2022 and their species richness was estimated applying non-parametrical statistical methods (Chao-1 and Abundance-based Coverage Estimator) to account for incomplete detection. A total of 18 species were found amongst the five sites. A maximum of 12 species were recorded in each single site, while estimates suggest that another 1-3 species were likely undetected. Species composition were found highly variable also between sites with similar species richness.

Re-evaluating and dating myriapod diversification with phylotranscriptomics under a regime of dense taxon sampling

Recent transcriptomic studies of myriapod phylogeny have been based on relatively small datasets with <40 myriapod terminals and variably supported or contradicted the traditional morphological groupings of Progoneata and Dignatha. Here we amassed a large dataset of 104 myriapod terminals, including multiple species for each of the four myriapod classes. Across the tree, most nodes are stable and well supported. Most analyses across a range of gene occupancy levels provide moderate to strong support for a deep split of Myriapoda into Symphyla + Pauropoda (=Edafopoda) and an uncontradicted grouping of Chilopoda + Diplopoda (=Pectinopoda nov.), as in other recent transcriptome-based analyses; no analysis recovers Progoneata or Dignatha as clades. As in all recent multi-locus and phylogenomic studies, chilopod interrelationships resolve with Craterostigmus excluded from Amalpighiata rather than uniting with other centipedes with maternal brood care in Phylactometria. Diplopod ordinal interrelationships are largely congruent with morphology-based classifications. Chilognathan clades that are not invariably advocated by morphologists include Glomerida + Glomeridesmida, such that the volvation-related characters of pill millipedes may be convergent, and Stemmiulida + Polydesmida more closely allied to Juliformia than to Callipodida + Chordeumatida. The latter relationship implies homoplasy in spinnerets and contradicts Nematophora. A time-tree with nodes calibrated by 25 myriapod and six outgroup fossil terminals recovers Cambrian-Ordovician divergences for the deepest splits in Myriapoda, Edafopoda and Pectinopoda, predating the terrestrial fossil record of myriapods as in other published chronograms, whereas age estimates within Chilopoda and Diplopoda overlap with or do not appreciably predate the calibration fossils. The grouping of Chilopoda and Diplopoda is recovered in all our analyses and is formalized as Pectinopoda nov., named for the shared presence of mandibular comb lamellae. New taxonomic proposals for Chilopoda based on uncontradicted clades are Tykhepoda nov. for the three blind families of Scolopendromorpha that share a "sieve-type" gizzard, and Taktikospina nov. for Scolopendromorpha to the exclusion of Mimopidae.

Two new species of the dwarf centipede genus Nannarrup Foddai, Bonato, Pereira & Minelli, 2003 (Chilopoda, Geophilomorpha, Mecistocephalidae) from Japan

The genus Nannarrup Foddai, Bonato, Pereira & Minelli, 2003 is a monotypic genus established on the basis of the possibly introduced species N.hoffmani Foddai, Bonato, Pereira & Minelli, 2003, from New York, USA. In the present study, in a field survey conducted throughout Japan, Nannarrup-like specimens were collected from Honshu, Shikoku, and Kyushu. These specimens clearly showed the diagnostic characteristics of the genus but were morphologically distinct from N.hoffmani. Furthermore, morphological analysis and DNA barcoding revealed that these specimens could be assigned to two distinct undescribed species. On the basis of these results, N.innuptus Tsukamoto, sp. nov. and N.oyamensis Tsukamoto, sp. nov. are described. The three Nannarrup species can be distinguished from each other on the basis of the following combination of characteristics: presence or absence of a pair of smooth or weakly areolate areas along the posterior part of the paraclypeal sutures; the width-to-length ratio of the denticle on the trochanteroprefemur; the pigmentation of the denticle on the tarsungulum. Moreover, the field survey resulted in the collection of exclusively female specimens of N.innuptus Tsukamoto, sp. nov., which shows the possibility of parthenogenesis of this species.

Novel mitochondrial gene rearrangements pattern in the millipede Polydesmus sp. GZCS-2019 and phylogenetic analysis of the Myriapoda

The subphylum Myriapoda included four extant classes (Chilopoda, Symphyla, Diplopoda, and Pauropoda). Due to the limitation of taxon sampling, the phylogenetic relationships within Myriapoda remained contentious, especially for Diplopoda. Herein, we determined the complete mitochondrial genome of Polydesmus sp. GZCS-2019 (Myriapoda: Polydesmida) and the mitochondrial genomes are circular molecules of 15,036 bp, with all genes encoded on + strand. The A+T content is 66.1%, making the chain asymmetric, and exhibits negative AT-skew (-0.236). Several genes rearrangements were detected and we propose a new rearrangement model: "TD (N\R) L + C" based on the genome-scale duplication + (non-random/random) loss + recombination. Phylogenetic analyses demonstrated that Chilopoda and Symphyla both were monophyletic group, whereas Pauropoda was embedded in Diplopoda to form the Dignatha. Divergence time showed the first split of Myriapoda occurred between the Chilopoda and other classes (Wenlock period of Silurian). We combine phylogenetic analysis, divergence time, and gene arrangement to yield valuable insights into the evolutionary history and classification relationship of Myriapoda and these results support a monophyletic Progoneata and the relationship (Chilopoda + (Symphyla + (Diplopoda + Pauropoda))) within myriapod. Our results help to better explain the gene rearrangement events of the invertebrate mitogenome and lay the foundation for further phylogenetic study of Myriapoda.

When SEM becomes a deceptive tool of analysis: the unexpected discovery of epidermal glands with stalked ducts on the ultimate legs of geophilomorph centipedes

BACKGROUND

The jointed appendage is a key novelty in arthropod evolution and arthropod legs are known to vary enormously in relation to function. Among centipedes, the ultimate legs always are distinctly different from locomotory legs, and different centipede taxa evolved different structural and functional modifications. In Geophilomorpha (soil centipedes), ultimate legs do not participate in locomotion and were interpret to serve a sensory function. They can be sexually dimorphic and in some species, male ultimate legs notably appear "hairy". It can be assumed that the high abundance of sensilla indicates a pronounced sensory function. This study seeks for assessing the sensory diversity, however, documents the surprising and unique case of an extensive glandular epithelium in the ultimate legs of three phylogenetically distant species.

RESULTS

The tightly aggregated epidermal glands with stalked ducts - mistakenly thought to be sensilla - were scrutinized using a multimodal microscopic approach comprising histology as well as scanning and transmission electron microscopy in Haplophilus subterraneus. Hence, this is the first detailed account on centipede ultimate legs demonstrating an evolutionary transformation into a "secretory leg". Additionally, we investigated sensory structures as well as anatomical features using microCT analysis. Contrary to its nomination as a tarsus, tarsus 1 possesses intrinsic musculature, which is an indication that this podomere might be a derivate of the tibia.

DISCUSSION

The presence and identity of ultimate leg associated epidermal glands with stalked ducts is a new discovery for myriapods. A pronounced secretory as well as moderate sensory function in Haplophilus subterraneus can be concluded. The set of characters will improve future taxonomic studies, to test the hypotheses whether the presence of these specialized glands is a common feature in Geophilomorpha, and that tarsus 1 may be a derivate of the tibia. As the number of epidermal glands with stalked ducts is sexually dimorphic, their function might be connected to reproduction or a sex-specific defensive role. Our results, in particular the unexpected discovery of 'glandular hairs', may account for a striking example for how deceptive morphological descriptions of epidermal organs may be, if based on non-invasive techniques alone.

A new soil centipede from South-East Asia with a unique arrangement of ventral glands, and a revised synopsis of Gonibregmatidae (Chilopoda, Geophilomorpha)

A new gonibregmatid centipede, Vinaphilusunicus gen. n., sp. n., is described based on two females from a single location in northern Vietnam. The new genus and species are distinguished mainly by the arrangement of the ventral pore-fields, which is unique among all Chilopoda. A critically revised synopsis of the Gonibregmatidae is also given. In particular, three species are provisionally recognized in Himatosoma Pocock, 1891: H.bidivisum Silvestri, 1919, H.porosum Pocock, 1891 (= H.typicumtridivisum Silvestri, 1919, syn. n.), and H.typicum Pocock, 1891. The genera Dschangelophilus Verhoeff, 1937 and Tweediphilus Verhoeff, 1937, with their species D.coloratus Verhoeff, 1937 and T.malaccanus Verhoeff, 1937, are moved to the Gonibregmatidae, whereas Geoporophilusaporus Attems, 1930 is moved to the Oryidae as Orphnaeusaporus (Attems, 1930), comb. n.

Exploring Phylogenetic Relationships within Myriapoda and the Effects of Matrix Composition and Occupancy on Phylogenomic Reconstruction

Myriapods, including the diverse and familiar centipedes and millipedes, are one of the dominant terrestrial arthropod groups. Although molecular evidence has shown that Myriapoda is monophyletic, its internal phylogeny remains contentious and understudied, especially when compared to those of Chelicerata and Hexapoda. Until now, efforts have focused on taxon sampling (e.g., by including a handful of genes from many species) or on maximizing matrix size (e.g., by including hundreds or thousands of genes in just a few species), but a phylogeny maximizing sampling at both levels remains elusive. In this study, we analyzed 40 Illumina transcriptomes representing 3 of the 4 myriapod classes (Diplopoda, Chilopoda, and Symphyla); 25 transcriptomes were newly sequenced to maximize representation at the ordinal level in Diplopoda and at the family level in Chilopoda. Ten supermatrices were constructed to explore the effect of several potential phylogenetic biases (e.g., rate of evolution, heterotachy) at 3 levels of gene occupancy per taxon (50%, 75%, and 90%). Analyses based on maximum likelihood and Bayesian mixture models retrieved monophyly of each myriapod class, and resulted in 2 alternative phylogenetic positions for Symphyla, as sister group to Diplopoda + Chilopoda, or closer to Diplopoda, the latter hypothesis having been traditionally supported by morphology. Within centipedes, all orders were well supported, but 2 deep nodes remained in conflict in the different analyses despite dense taxon sampling at the family level. Relationships among centipede orders in all analyses conducted with the most complete matrix (90% occupancy) are at odds not only with the sparser but more gene-rich supermatrices (75% and 50% supermatrices) and with the matrices optimizing phylogenetic informativeness or most conserved genes, but also with previous hypotheses based on morphology, development, or other molecular data sets. Our results indicate that a high percentage of ribosomal proteins in the most complete matrices, in conjunction with distance from the root, can act in concert to compromise the estimated relationships within the ingroup. We discuss the implications of these findings in the context of the ever more prevalent quest for completeness in phylogenomic studies.

The first geophilid centipedes from Malesia: a new genus with two new species from Sumatra (Chilopoda, Geophilidae)

A new genus Sundageophilus is here described for two new species of geophilid centipedes (Chilopoda: Geophilidae) from Sumatra, Indonesia. Both Sundageophilus bidentatus sp. n. and Sundageophilus poriger sp. n. feature a minute body size (less than 1 cm long with 31-35 pairs of legs), a similar structure of the maxillae, elongated forcipules, and few coxal organs. Sundageophilus bidentatus is unique among geophilids because the ultimate article of the forcipule is armed with two conspicuous denticles, one dorsal to the other, instead of a single one or none. The two species of Sundageophilus are the first genuine Geophilidae ever found in Malesia, and among the very few representatives of this family in the entire south-eastern Asia.

Taxonomic revision of Stigmatomma Roger (Hymenoptera: Formicidae) in the Malagasy region

In this study we present the first taxonomic revision of the ant genus Stigmatomma in the Malagasy biogeographic region, re-describe the previously known S. besucheti Baroni-Urbani, and describe seven new species to science (S. bolabola sp. n., S. irayhady sp. n., S. janovitsika sp. n., S. liebe sp. n., S. roahady sp. n., S. sakalava sp. n., and S. tsyhady sp. n.). The revision is based on the worker caste, but we provide brief descriptions of gynes and males for some species. Species descriptions, diagnosis, character discussion, identification key, and glossary are illustrated with 360 high-quality montage and SEM images. The distribution of Stigmatomma species in Madagascar are mapped and discussed within the context of the island's biomes and ecoregions. We also discuss how some morphometric variables describe the differences among the species in the bioregion. Open science is supported by providing access to R scripts, raw measurement data, and all specimen data used. All specimens used in this study were given unique identifies, and holotypes were imaged. Specimens and images are made accessible on AntWeb.org.

Tentorial mobility in centipedes (Chilopoda) revisited: 3D reconstruction of the mandibulo-tentorial musculature of Geophilomorpha

Mandibular mechanisms in Geophilomorpha are revised based on three-dimensional reconstructions of the mandibulo-tentorial complex and its muscular equipment in Dicellophiluscarniolensis (Placodesmata) and Hydroschendylasubmarina (Adesmata). Tentorial structure compares closely in the two species and homologies can be proposed for the 14/17 muscles that attach to the tentorium. Both species retain homologues of muscles that in other Pleurostigmophora are traditionally thought to cause swinging movements of the tentorium that complement the mobility of the mandibles. Although the original set of tentorial muscles is simplified in Geophilomorpha, the arrangement of the preserved homologues conforms to a system of six degrees of freedom of movement, as in non-geophilomorph Pleurostigmophora. A simplification of the mandibular muscles is confirmed for Geophilomorpha, but our results reject absence of muscles that in other Pleurostigmophora primarily support see-saw movements of the mandibles. In the construction of the tentorium, paralabial sclerites seem to be involved in neither Placodesmata nor Adesmata, and we propose their loss in Geophilomorpha as a whole. Current insights on the tentorial skeleton and its musculature permit two alternative conclusions on their transformation in Geophilomorpha: either tentorial mobility is primarily maintained in both Placodesmata and Adesmata (contrary to Manton's arguments for immobility), or the traditional assumption of the tentorium as being mobile is a misinterpretation for Pleurostigmophora as a whole.

First results of the German Barcode of Life (GBOL) - Myriapoda project: Cryptic lineages in German Stenotaenialinearis (Koch, 1835) (Chilopoda, Geophilomorpha)

As part of the German Barcode of Life (GBOL) Myriapoda program, which aims to sequence the COI barcoding fragment for 2000 specimens of Germany's 200 myriapod species in the near future, 44 sequences of the centipede order Geophilomorpha are analyzed. The analyses are limited to the genera Geophilus Leach, 1814 and Stenotaenia Koch, 1847 and include a total of six species. A special focus is Stenotaenia, of which 19 specimens from southern, western and eastern Germany could be successfully sequenced. The Stenotaenia data shows the presence of three to four vastly different (13.7-16.7% p-distance) lineages of the genus in Germany. At least two of the three lineages show a wide distribution across Germany, only the lineage including topotypes of Stenotaenialinearis shows a more restricted distribution in southern Germany. In a maximum likelihood phylogenetic analysis the Italian species Stenotaenia 'sorrentina' (Attems, 1903) groups with the different German Stenotaenialinearis clades. The strongly different Stenotaenialinearis lineages within Germany, independent of geography, are a strong hint for the presence of additional, cryptic Stenotaenia species in Germany.

Molecular-based estimate of species number, phylogenetic relationships and divergence times for the genus Stenotaenia (Chilopoda, Geophilomorpha) in the Italian region

Stenotaenia is one of the largest and most widespread genera of geophilid centipedes in the Western Palearctic, with a very uniform morphology and about fifteen species provisionally recognized. For a better understanding of Stenotaenia species-level taxonomy, we have explored the possibility of using molecular data. As a preliminary assay, we sampled twelve populations, mainly from the Italian region, and analyzed partial sequences of the two genes COI and 28S. We employed a DNA-barcoding approach, complemented by a phylogenetic analysis coupled with divergence time estimation. Assuming a barcoding gap of 10-16% K2P pairwise distances, we found evidence for the presence of at least six Stenotaenia species in the Italian region, which started diverging about 50 million years ago, only partially matching with previously recognized species. We found that small-sized oligopodous species belong to a single clade that originated about 33 million years ago, and obtained some preliminary evidence of the related genus Tuoba being nested within Stenotaenia.

At the end of the rope: Geophilushadesi sp. n. - the world's deepest cave-dwelling centipede (Chilopoda, Geophilomorpha, Geophilidae)

A new geophilomorph centipede, Geophilushadesi sp. n., is described from caves in the Velebit Mountain, central Croatia. Together with Geophiluspersephones Foddai & Minelli, 1999, described from Pierre Saint-Martin cave in France, they are the only two remarkably troglomorphic geophilomorphs hitherto known. The new species apparently belongs to a group of Geophilus species inhabiting mainly Western and Southern Europe, with a uniquely modified pretarsus in the second maxillae. Geophilushadesi sp. n. shows unusual traits, some of which commonly found in troglobitic arthropods, including exceptionally elongated antennae, trunk segments and leg claws. The species is described upon specimens found in two caves at a depth below -250 m. Another two specimens apparently belonging to the same species have been recorded in another deep vertical cave at -980 m and -1100 m. The latter represents the world's deepest record of Chilopoda as a whole.

Population genetic structure of a centipede species with high levels of developmental instability

European populations of the geophilomorph centipede Haplophilus subterraneus show a high proportion of individuals with morphological anomalies, suggesting high levels of developmental instability. The broad geographic distribution of this phenomenon seems to exclude local environmental causes, but the source of instability is still to be identified. The goal of the present study was to collect quantitative data on the occurrence of phenodeviants in different populations, along with data on the patterns of genetic variation within and between populations, in order to investigate possible association between developmental instability and genetic features. In a sample of 11 populations of H. subterraneus, distributed in western and central Europe, we looked for phenodeviants, in particular with respect to trunk morphology, and studied genetic variation through the genotyping of microsatellite loci. Overall, no support was found to the idea that developmental instability in H. subterraneus is related to a specific patterns of genetic variation, including inbreeding estimates. We identified a major genetic partition that subdivides French populations from the others, and a low divergence among northwestern areas, which are possibly related to the post-glacial recolonization from southern refugia and/or to recent anthropogenic soil displacements. A weak correlation between individual number of leg bearing segments and the occurrence of trunk anomalies seems to support a trade-off between these two developmental traits. These results, complemented by preliminary data on developmental stability in two related species, suggest that the phenomenon has not a simple taxonomic distribution, while it exhibits an apparent localization in central and eastern Europe.

Cell size versus body size in geophilomorph centipedes

Variation in animal body size is the result of a complex interplay between variation in cell number and cell size, but the latter has seldom been considered in wide-ranging comparative studies, although distinct patterns of variation have been described in the evolution of different lineages. We investigated the correlation between epidermal cell size and body size in a sample of 29 geophilomorph centipede species, representative of a wide range of body sizes, from 6 mm dwarf species to gigantic species more than 200 mm long, exploiting the marks of epidermal cells on the overlying cuticle in the form of micro-sculptures called scutes. We found conspicuous and significant variation in average scute area, both between suprageneric taxa and between genera, while the within-species range of variation is comparatively small. This supports the view that the average epidermal cell size is to some extent taxon specific. However, regression analyses show that neither body size nor the number of leg-bearing segments explain this variation, which suggests that cell size is not an usual target of change for body size evolution in this group of arthropods, although there is evidence of its correlation with other morphological variables, like cuticle thickness. Scute sizes of miniaturized geophilomorph species are well within the range of the lineage to which the species belong, suggesting recent evolutionary transitions to smaller body size.