Amypteride🏳️‍⚧️🔻🕷🦂

@amypteride

Médiatrice scientifique Paleontology MSc graduate, now science educator Chelicerates lover🕷🦂❤️ & inverts>verts , all living things are beautiful❤️ #Cheliceratime is here Superman stan Elle/She🏳️‍⚧️-Fr/En All my things:

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Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 17d

And to end today's topic, the usual drawing auto-feedback and (a lot of) refs! Thank you for reading & I’ll see you on the next #Cheliceratime! 4/4

Is this drawing accurate ?

I like it, I love this species so I’m happy to add it to the Cheliceratime’s entries! :D

How much dorsal markings can be obvious varies a lot depending on each individual, mine here is pretty standard for a female.

Brightness can vary depending on the light & specimen considered.

Claws may be a bit oversized but I wanted them to be visible.

REFERENCES

• Jocqué R. & Dippenaar-Schoeman A.S., 2007. Spider Families of the World. 2° Edition, Royal Museum of Central Africa, 336 pp.

• Korenko S., Pekár S. & Honěk A., 2010. Predation activity of two winter-active spiders (Araneae: Anyphaenidae, Philodromidae). Journal of Thermal Biology 35(2), p. 112-116.

· Kulkarni S., Wood H.M., Hormiga G., 2023. Advances in the reconstruction of the spider tree of life: A roadmap for spider systematics and comparative studies. Cladistics 39, p. 479–532.

• Labarque F.M, Soto E.M., Ramírez M.J. & Arnedo M.A., 2015. Chasing ghosts: the phylogeny of Amaurobioidinae ghost spiders (Araneae, Anyphaenidae). Zoologica Scripta 44(5), p. 550-561.

• Ramírez M., 1995. A phylogenetic analysis of the subfamilies of Anyphaenidae (Arachnida, Araneae). Insect Systematics & Evolution 26. p. 361-384.

• Roberts M. J .. 2009 (French trad.) Guide des araignees de France et d'Europe. Delachaux & Niestle. 383 pp.

• Wheeler et al., 2017. The spider tree of life: phylogeny of Araneae based on target-gene analyses from an extensive taxon sampling. Cladistics 33(6), p. 574-616.

Les carnets nature de Jessica, 2025. Araignée Citroën (Anyphaena accentuata). Online at https://jessica-joachim.com/arachnides-2/arachnides/anyphaenidae/araignee-citroen-anyphaena-accentuata/

Anyphaena accentuata - World Spider Catalog
https://wsc.nmbe.ch/spec-data/8500/Anyphaena_accentuata

Anyphaena accentuata - araneae Spiders of Europe
https://araneae.nmbe.ch/data/43/Anyphaena_accentuata

INaturalist, 2026. Anyphaena accentuata. Online at https://www.inaturalist.org/taxa/319828-Anyphaena-accentuata

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 17d

This European species of ghost spider is a frequent sigth among european spider communities, and is a nocturnal animal with a funny French nickname. #Cheliceratime 3/4

Anyphaena accentuata is a member of the family Anyphaenidae, also known as ghost spiders or buzzing spiders (in reference to the behavior discussed earlier). These spiders have a mostly American, Australasian & Eurasian distribution but are unusually rarer in Europe, A. accentuata representing virtually the entire diversity of the family on the continent outside of the Mediterranean, while dozens are known from some areas of the Americas. This makes it one of the easiest spiders to identify for European beginners.

The slide also shows a map of the world illustrating the text and in which the Americas contain a lot of species, as well as Europe due to the wide distribution of A. accentuata

Anyphaenids are part of the dionychans, a major group of wandering spiders equipped with diagnostic adhesive setae at the tip of their legs. This large assemblage includes jumping spiders, ground spiders or wall spiders, anyphaenids being more closely related to the clubionids (“sac spiders). The family is split into several subfamilies and A. accentuata, besides being the species of reference for the whole family, is often retrieved as an early diverging member of the anyphaenines.

The slide also contains a phylogenetic tree of dionychan spiders in which anyphaenids are split into 3 subfamilies: the malenellines, the amaurobiodines and the anyphaenines (including Anyphaena accentuata).

This spider is a nocturnal animal, hiding through the day in spun leaves transformed into a hideout thanks to a silk cocoon, like the closely related clubionids do. Anyphaena accentuata is a pursuit & ambush hunter, hunting virtually anything suiting its needs and size. Studies on its hunting habits showed a certain impact of ambient temperatures on this spider’s hunting. It seems to display a higher tolerance to cold than other similar (ecologically speaking) spiders, adjusting its metabolism to stay active even near 0°C, while being more sensible to heat.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 17d

You know the drill, let's talk about its morphology, distribution & life cycle first to meet this spider. #Cheliceratime 2/4

Anyphaena accentuata is a species of ghost spider with an overall light yellow to grey coloration, with darker spots on the legs and prosoma’s sides of variable intensity depending on which individual you’re looking at. It exhibits the classic body plan of a wandering spider, with eyes clustered at the body front, long but strong legs ideal for running and spinnerets placed at the most posterior end of the body.

This species is mostly known for its singular markings right in the middle of the opisthosoma’s dorsal side, looking like 2 pairs of angled, black median spots.

Males and females differ mainly on colors & morphology rather than size (even tho females are slightly larger). Males have more contrasted & darker colorations, slender legs and, as it’s often the case among spiders and especially non-spinning ones, thinner opisthosoma. While having dark marks on the opisthosoma is shared by many other species of Anyphaena, A. accentuata stands out by having its marks clearly visible and rather short & well centered.

Male main body length: 4-7 mm
Female main body length: 5-9mm

Anyphaena accentuata is known in all of Europe, its distribution being mainly confined by the mid-Eurasian mountain chains delimiting Europe from Asia. It makes it a common sight among East Eurasian spider communities and a firmly temperate to Mediterranean species of the Palearctic realm.

This species lives on plants of all sizes, from grasses & shrubs to trees. They are most frequently seen on leaves of deciduous trees & high grasses in spring & summer, while hiding under barks and in the soil in colder times.

This species (and the Anyphaena genus as a whole) owns its name of buzzing spider due to the unique reproductive behavior of the males: they vibrate their opisthosoma and hit their pedipalps in a drum-like fashion, signaling their presence to females for mating. Impressive enough relative to the size of the animal, the sounds produced can be heard by humans, making it one a the few spiders to produce sounds we can hear. After mating, the female lays her eggs on a leaf and guards them from a safe distance.

This species is most abundant during northern spring & summer. Females can endure almost an entire year by hiding through winter, while males vanish during winter.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 17d

What time is it? It’s #Cheliceratime & #Spidersaturday ! Today in Cheliceratime the most widespread species of buzzing spider, Anyphaena accentuata! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️🧵 #spider #arachnid #citroen #sciart #bugsky #invert

This wandering spider is a nocturnal species, mainly active on plants’ leaves & stems. It’s sometimes called “Citroën spider” in French due to the marks on its back.

Size: 7mm of body length
Time period: Holocene (present day)
Conservation status: Least concern/Near threatened

The animal drawn is a pale-looking spider with slightly brown-ish marks on its back

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 20d

And of course: the usual drawing auto feedback & references, thank you for reading I’ll see you on the next #Cheliceratime! I'm really happy to have covered this one, I've been waiting for years this kind of animal to have a clearer view on chelicerates' origins! :D 6/6

Is this paleoart accurate?
Not that much to be said, its morphology is taken straight from the 2026 description, I like how it ended.

I chose to draw 15 thoracic segments since the specimens of the new study all have this count, but 14 segments would also have been accurate.

I liked the blue tone of the flaps on the publication’s paleoart so I kept the idea.

I hid most of the thoracic walking legs under the flaps while making the ones of the head stand out more, since it both fits what’s seen on fossils and it helsp to give it a look giving megacheiran x chelicerate fusion vibes.

REFERENCES

· Aria C. & Caron J.-B., 2019. A middle Cambrian arthropod with chelicerae and proto-book gills. Nature 573, p. 586–589.

· Dunlop J.A. & Lamsdell J.C., 2017. Segmentation and tagmosis in Chelicerata. Arthropod Structure & Development 46, p. 395–418.

· Lerosey-Aubril R. & Ortega-Hernández J., 2026. A chelicera-bearing arthropod reveals the Cambrian origin of chelicerates. Nature 652, p. 931–937.

· Liu Y., Lustri L., Mai H., Williams M., Liu L., Tang Y., Harvey T.H.P. & Hou X., 2026. Urokodia sheds light on the origin of chelicerae and book gills of Chelicerata. Nature, 7 pp.

· Saleh F., Qi C., Buatois L.A., Mángano M.G., Paz M., Vaucher R., Zheng Q., Hou X.-G., Gabbott S.E. & Ma X., 2022. The Chengjiang Biota inhabited a deltaic environment. Nature Communications 13, 1569, 9 pp.

• Sharma P.P. & Gavish-Regev E., 2025. The Evolutionary Biology of Chelicerata. Annual Review of Entomology 70, p. 143–163.

Colorado Plateau Geosystems Inc., 2026.
Global Series. In DeepTimeMaps. Online at https://deeptimemaps.com/map-lists-thumbnails/global-series/

The ICS international chronostratigraphic chart 2025. Episodes 2025. Online at https://stratigraphy.org/chart

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 20d

How chelicerates came to be has been an difficult topic since a loooong time, and discoveries such as Urokodia's revision are extremely important in understanding it, proving how fossils can bridge the gaps in evolution. #Cheliceratime 5/6

Why this discovery is so important is because of how little we knew about Cambrian chelicerates for a long time. For decades, Chelicerates were seen as an almost post-Cambrian group, with only a few taxa like Sanctacaris or Cambropycnogon recognized as cambrian chelicerates. However, with time, phylogenies of putative stem chelicerates, of various chelicerates groups and discoveries of animals looking like blends of primitive and derived features, it became clear the group had deep cambrian origins, but these considerations hit a wall when faced with the issue of that too few data & species were known.

Early 2000's => Sanctacaris & Cambropycnogon and few minor attempts

2010's => Phylogenies suggest links with habelids, mollisonids & megacheirans

2020's => Enlarged sampling, Urokodia & Megachelicerax discovery confirms hypotheses

The rise of the discovery rate of cambrian chelicerates is still happening, the 2020's being noticeably productive on the matter, making the topic as a whole subject to changes each time a new species is described. 2026, as of now, provided key species on this topic, with Megachelicerax cousteaui proving chelicerates existed in the Cambrian and that they had a lot in common with habellids and mollisonids. Where Urokodia aequalis new interpretation is important is that it fixes one of these major data issues by bridging this time habellids & mollisonids (and by extension chelicerates) with megacheirans, giving a now way clearer view on this transition than what we tinker with for the last 2 decades.

Urokodia can be seen as a transitional form between megacheirans and stem chelicerates with its proto-chelicerae and prosoma-like front part, while Megachelicerax is closer to be a transitional form between stem & true chelicerates with its chelicerae & book gills

However, several blindspots, independent from Urokodia aequalis itself, remain in the way of properly assessing the early diversification of chelicerates, especially the abundance of ghost lineages blurring the picture of the early branchings of chelicerates’ evolution. Pycnogonids are one of the biggest problems at play in this mess: they are lil’ aliens with a body plan so extreme that it’s very difficult to imagine how they evolved from animals looking like U. aequalis. In light of recent studies, their morphology seems to be an extremely derived condition, with a split of the original 7-segmented prosoma. The internal relationships of euchelicerates are also unclear and arthropods had faster evolutionary rates in the Cambrian than today, blurring lineages splits.

Such revisions as what was done on Urokodia aequalis are exactly why re-examinations of already known cambrian critters with modern technology & methods are an important topic in arthropod paleontology. These works show that we already had some answers right under our noses for a long time, and that this kind of monitoring work is as important as discovering new species, both, in the end, helping to uncover the mysteries of how modern animals originated. With the 2026's discoveries, how chelicerates came to be is way clearer than before, helping to solve one of chelicerates evolution’s biggest issues. And sometimes, such works were made possible thanks to the ideas phylogenies hinted at first and were later confirmed by fossils. Chelicerates evolution is sometimes a hot topic with strong divergences, but it’s only when taking into account all methods, with their strength and limitations, that getting a clearer picture becomes possible, and that’s something I aimed to do with Cheliceratime too.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 20d

Between the first appendage looking like a proto-chelicerae, its breathing appendages looking like proto-book gills and its head part having the same structure as a chelicerate prosoma, this arthropod is a blend of megacheiran & chelicerate features. #Cheliceratime 4/6

The most important feature is the morphology of the first appendage. Its 4-segmented look makes it a lot similar to the great appendage of megacheirans, but functionally, the reduction of the 3° & 4° segments made it works like a pincer claw, which is literally what a chelicera is.

(the slide includes a succsion of the structures that appeared through early chelicerates evolution)
Megacheirans (4-segmented, long grasping appendage)
=>
Urokodia aequalis (4-segmented, short pincer claw)
=>
Stem chelicerates (Mollisonids here) (2-segmented, short pincer claw)
=>
True chelicerates (3-segmented, pincer claw)

This is extremely important because it finally gives a template of how megacheirans’ great appendages reduced and turned into pincer claws, something that was hinted at for a long time by phylogenies but for which we didn’t have a transitional form showing the in-between. U. aequalis provides some clue on which segments reduced and how joints evolved, but also bridges the morphologies of the megacheiran state with the early chelicerae of mollisonids & true chelicerates.

Another significant feature is the structure of the flaps of the legs. It shows a superposition of several layers in a fashion unlike trilobites but rather similar to mollisonids and habelians, which are stem chelicerates. Most importantly, this looks a lot like a proto-book gill with numerous layers of organic tissues maximizing the breathing area, something that is found all across the chelicerates’ evolutionary tree.

(the slide includes a succsion of the structures that appeared through early chelicerates evolution)
Megacheirans (Basic arthropod biramous appendage)
=>
U. aequalis & Stem chelicerates (Multi-layered flap appendages, reduction of the walking part)
=>
True chelicerates (Book gills)

This is extremely important too because aquatic chelicerates have a highly modified breathing system, the book gills being unique to this group and the basis from which spiders & scorpions evolved their book lungs, through interiorization of the gills. This discovery shows that this feature started evolving even before chelicerae appeared since it has also been retrieved among some megacheirans, making it a key feature in chelicerates’ early evolution.

And another one because third’s the charm, something really significant is the segmentation pattern of the animal’s body.

Megacheirans and artiopods usually have a basic arthropod head, made from the fusion of the first 6 body segments (the eye segment + 5 appendaged segments), while recent studies tend to firmly support that chelicerates had primitively a clearly 7-segmented front body part. U. aequalis, despite having a lot of megacheiran features, doesn’t have a 5-segmented head but have 7 segments fused together, which is the ground pattern of a chelicerate’s prosoma, making it by far the oldest occurrence of this feature among arthropods.

All these features give to Urokodia aequalis a really special place among the stem group from which arose chelicerates. Phylogenetical analyses retrieved it right between megacheirans and more derived groups like mollisonids & habellids with undoubtful chelicerate features, connecting the dots of how cheliceromorphs changed over time from megacheirans to the ancestors of modern chelicerates, and giving a face made of a blend of the 2 extremes of this transition.

The slide comprises a phylogenetic tree in which Urokodia aequalis is the sister group to mollisonids+habellids+chelicerates, solidifying its transitionnal nature between the ancestral megacheiran-like state and the more derived chelicerate condition with a 7-segmented front body part, chelicerae and book gills

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 20d

Aaaaan now it's time to talk about morphology a bit more, and this morphology is a bit unusual, because this species may be the kind of transitionnal forms we've been searching for years. #Cheliceratime 3/6

The head part of the animal checks a lot of boxes of what’s expected from a primitive chelicerate:

Stalked compound eyes, like many primitive arthropods.

A frontal tagma made of the fusion of the first 7 body segments, which is still the pattern that chelicerates go with today, their prosoma having 6 pairs of appendages like what’s seen on U. aequalis.

A first appendage 4-segmented like a megacheiran but with noticeably reduced segments, giving it a pincer claw-like function, like a chelicerae.

Biramous legs with both a walking & breathing part.

The rest of the body is mainly made of a thorax of 14 to 15 segments depending on the individual (could very be linked to the growth of the animal, trilobites grew by adding segments between in their thorax for example). The body ended with a large fluke-like part, probably useful for swimming.

Even tho most of the body segments bear biramous appendages (11 segments, just as many marine extinct chelicerates have), the ones towards the body end only have flap-like appendages, showing a somewhat specialisation of the body end for other purposes than walking.

The discovery of this species didn’t make a lot of noise compared to the one of Megachelicerax cousteaui a few months earlier, that provided unrefutable proof of chelicerates in Middle Cambrian. Even tho this confirmed a lot of suspicions that grew in the last years concerning an already well-established chelicerate diversity back then, it’s safe to say it didn’t really helped in understanding how chelicerates came to be.

Because, unlike Megachelicerax cousteaui that is already a fully fleshed out chelicerate with an anatomy checking all the classical boxes of what is a chelicerate (3-segmented chelicerae, book gills-like appendages, a body divided into a prosoma & an opisthosoma and so on), Urokodia aequalis looks rather like the transitional form that phylogenies have been hinting at for the last 15 years on how chelicerates came to be from more primitive arthropods.

Is this a missing link?
NO.

The idea that extinct species with a blend of primitive & derived features would be direct links between older & newer groups is an outdated notion that went obsolete as scientists realized evolution never was a straight line, even more when each species is unique and can live alongside close relatives equally derived that retained some other primitive features.
We tend to talk more about “transitional forms” now to illustrate how in a bigger scheme, some species provide key template on how some features changed among a group across time, and so without drawing a straight line between possibly unrelated species.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 20d

First, let's talk a bit about its discovery, paleoenvironment and a bit of general anatomy before going further. #Cheliceratime 2/6

Urokodia aequalis is an extinct primitive arthropod, first named in 1989. It’s known from the Maotianshan Shales, a famous Chinese geological Formation from the Middle Cambrian.

Even tho it’s been known for 37 years, paleontologists kinda had a hard time to figure out what this animal was, its identification shifting from an unknown basal arthropod, a relative of trilobites or a stem chelicerate depending on the teams & methods used. However, and that’s why we’re talking about it today

Urokodia aequalis lived 518 million years ago during the late Furongian epoch. Back then, some of the area that would become Southern China was underwater and in the Southern tropics. This habitat was a rather coastal environment with highly oxygenated waters that supported a rich ecosystem, sometimes disturbed by underwater landslides. Interestingly, the proximity to the mainland made this domain influenced by freshwater inputs too. U. aequalis was far from being an apex predator, and is mostly thought to be a small epibenthic predator, wandering on the sea bottom in search of food.

U. aequalis was part of the famous Chengjiang biota, which is one of the oldest known ecosystems including animals of modern phylums, that included, for example:

· Algeas
· Jellyfhishes
· Sponges
· Ctenophorans (Comb jellies)
· Brachiopods
· Mollusks
· Stem vertebrates
· Chaetognathes (arrow worms)
· Vetulicolians
· Trilobites
· Hymenocarines (“crustaceans”)
· Lobopods
· Stem chelicerates (megacheirans)
· Radiodonts (like Anomalocaris)

This animal was a medium small (around 3,5 cm long) arthropod known thanks to several specimens of fairly good conservation. Due to its general body shape with a long segmented thorax and a head shield & pygidium of rather similar sizes, it was though for some time to be part of the mollisonids, a group of stem chelicerates. Its assignation’s history was a bit chaotic, shifting a lot depending on the interpretations made on the fossil, going from a stem chelicerate to an artiopod (the group containing trilobites) to again a stem chelicerate.

And thanks to a super recent revision of the species, we have new insights on this criter’s anatomy that match quite well the stem chelicerate hypothesis.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 20d

What time is it? It’s #Cheliceratime ! This entry isn't technically about a chelicerate, but Urokodia aequalis recently bring new data on how chelicerates came to be! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️🧵 #paleoart #cambrian #arthropod 1/6

This ancient arthropod isn’t technicaly a chelicerate, but is the first species exemplifying clearly the hypothesized transitonal morphology of how the chelicerae & book gills of the chelicerates came to be from a more primitive arthropod body plan. This makes it an incredibly important animal in the understanding of chelicerates origins.

Size : 3 to 4-ish cm of body length
Time period : Middle Cambrian
Paleoart speculativometer : Few missing details

The animal drawn looks like a mix of a millipede with a flattened body end and a shrimp-like head but with very short legs and no antennae

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 25d

And of course: the usual drawing autofeedback & some references, thank you for reading I’ll see you on the next #Cheliceratime! 4/4

Is this paleoart accurate?
Really not that much to be said, it looks good but there aren’t many minute details known.

I decided to not put any appendages, synziphosurines’ classification is already complicated so unless I have some solid assurance on what I’m doing, I’m not gonna invent such things.

The color of the exoskeleton’s granulation isn’t based on any scientific data, I chose the color most likely to fit and contrast with the overall grey tone.

As the fossil suggests, I chose not to draw any eye.

REFERENCES

• Anderson L. & Wade R., 2003. Bembicosoma re-examined: A xiphosuran from the Silurian of the North Esk Inlier, Pentland Hills, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 94, p. 199 - 206.

• Garwood R.J., Dunlop J.A., 2023. Consensus and conflict in studies of chelicerate fossils and phylogeny. Arachnologische Mitteilungen: Arachnology Letters 66(1), p. 2-16.

• Lamsdell J.C, 2025. Codex Eurypterida: A Revised Taxonomy Based on Concordant Parsimony and Bayesian Phylogenetic Analyses. Bulletin of the American Museum of Natural History 473, 195 pp.

• Laurie M., 1899. XIX.—On a Silurian Scorpion and some additional Eurypterid Remains from the Pentland Hills. Transactions of the Royal Society of Edinburgh 39, p. 575-590.

· Lustri L., Antcliffe J.B., Gueriau P., Daley A.C., 2024. New specimens of Bunaia woodwardi Clarke, 1919 (Euchelicerata): a new member of Offacolidae providing insight supporting the Arachnomorpha. Royal Society Open Science 11(10), 240499, 21 pp.

• Lustri L., Gueriau P. & Daley A., 2024. Lower Ordovician synziphosurine reveals early euchelicerate diversity and evolution. Nature Communications 15.

• Sharma P.P. & Gavish-Regev E., 2025. The Evolutionary Biology of Chelicerata. Annual Review of Entomology 70, p. 143–163.

Dunlop J. A., Penney D. & Jekel D. 2023.
A summary list of fossil spiders and their relatives. In World Spider Catalog. Natural History Museum Bern, online at http://wsc.nmbe.ch, version 23.5.

The ICS international chronostratigraphic chart 2025. Episodes 2025. Online at https://stratigraphy.org/chart

Colorado Plateau Geosystems Inc., 2023 & 2026.
Europe & Global Series. In DeepTimeMaps . Online at https://deeptimemaps.com/map-lists-thumbnails/global-series/ & https://deeptimemaps.com/map-lists-thumbnails/europe/

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 25d

Bembicosoma is a great example of how much of a mess synziphosurines got and how much study them require to rethink our views on chelicerates' evolution, showing features and evolutionary pathways breaking simple ideas made by only taking into account major groups. #Cheliceratime 3/4

Bembicosoma pomphicus features sets it apart from the large popular groups of chelicerates such as eurypterids & horseshoe crabs, and place it into an informal group called “synziphosurines”, a grade comprising various extinct putative basal euchelicerates species of unclear affinities and from which emerged horseshoe crabs, eurypterids or the various arachnids lineages. B. pomphicus has no appendages recorded as of yet, but phylogenies have retrieved it for more than a decade to be more closely related and even part of the prosomapods (= crown group euchelicerates/extant euchelicerates, so possibly equal to Arachnida in regards to last decade’s research).

However, when diving a little bit into this mess, B. pomphicus is often retrieved as close to the bunodids, a family of Silurian synziphosurines including Bunodes and Limuloides. Despite support for this relationship being shaky, it’s supported on the basis of the shared enlargement of the 2° opisthosoma’s segment. If this hypothesis is correct, it would make Bembicosoma pomphicus a relative of the group that includes chasmataspidids, eurypterids and arachnopulmonates like scorpions, spiders or vinegarroons (apulmonate arachnids weren’t included).

The slide include a cladogram illustrating what's said before, in which B. pomphicus is related to the ancestors of eurypterids and chasmataspidids rather than to horseshoe crabs

The original eurypterid assignation of Bembicosoma pomphicus wasn’t based on nothing tho, and is a cool example of how fossil identification is often reliant on available knowledge and why periodic revisions are needed. Back in 1899, aquatic chelicerates were still poorly known and all housed under the name “merostomes”, and even were, not so long ago in the XIX° century, placed close to trilobites rather than arachnids. Eurypterid knowledge really took off in the 1910s with the extensive works on the North American eurypterids, while the synziphosurine revision is still ongoing since more or less 2 decades. The fragmentary remains of B. pomphicus, combined with the 1899 situation, were all factors that led to a now incorrect identification in light of more than a century of scientific progress (that you can learn more about in the following slide! :D)

Eurypterids have an opisthosoma firmly made of 12 dorsal segments, while this feature varies among basal chelicerates and is often closer to 10.

The sub-division of the opisthosoma with the 7 first segments being a bit larger is common across many eurypterids (called for them a “preabdomen, not to be confused with the and is similar to what B. pomphicus have (as with the lil’ pointy sides called epimeras).

Long ridges and a well defined cardiac lobe are often reduced or absent among eurypterids, while they are often kept among synziphosurines & horseshoe crabs (another reason why both groups are still often associated). Eurypterids are also known for their large eyes and appendages, while many synziphosurines show quite the opposite.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 25d

You know the drill, let's talk about its morphology, discovery & paleoenvironment first to meet this arthropod, known for 127 years by several specimens. #Cheliceratime 2/4

Bembicosoma pomphicus is an extinct basal euchelicerate that was first named in 1899 by Malcolm Laurie, a Scottish paleontologist, after fossils found in Upper Silurian rocks of the Pentland Hills. The species was at first considered to be an eurypterid, even tho Laurie himself highlighted this claim wasn’t that solid due to the specimens’ features. Funny thing I noticed while making the post you’re reading, the genus name was misspelled in the original description, written as “Bembycosoma”. It was re-described in 2003 as a synziphosurine.

Bembicosoma pomphicus lived around 435/432 million years ago, at the end of the Telychian Stage from Early Silurian. At that time, Scotland was in the Southern Hemisphere, on the front line of the upcoming collision between the lands that would become North America, then “Laurentia”, and Baltica, aka the Northern half of Modern Europe.

The area was partially covered by shallow seas and Bembicosoma pomphicus was one of the many animals thriving in such waters, especially eurypterids that are known from these deposits from several genera of various paleoecologies like Pentlandopterus, Stylonurus or Drepanopterus.

B. pomphicus is known by several specimens pointing to an animal of more or less 3 to 5 cm in length. The body is subdivided into a semi-circular prosoma, followed by an opisthosoma of 10 freely-articulated segments of decreasing width, and the whole thing ends with a small dagger-like telson. The main feature of the species is the texture of the exoskeleton, bearing numerous lil’ pustules giving it an overall granulated look. Legs are unknown.

Other few significant features can also be noted:

Eyes seem to be lacking, even tho the cuticle’s grooves of euchelicerates usually associated with eyes’ position are present.

Unlike several synziphosurines, there’s no genal spines on the prosoma’s sides.

The opisthosoma is subdivided into a larger mesosoma of 7 segments and a smaller metasoma of 3 segments.

The opisthosoma’s second segment is the largest to the point of calling it “hypertrophied” isn’t an understatement.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 25d

What time is it? It’s #Cheliceratime & #Fossilfriday! Today, a little eyeless chelicerate from the Silurian Period, Bembicosoma pomphicus! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️🧵 #arthropod #silurian #paleoart #sciart #bugsky #invert 1/4

This extinct euchelicerate was for a long time seen as either a close relative of eurypterids or as an eurypterid itself. It’s now considered to be a part of the synziphosurine grade from which arose eurypterids, horseshoe crabs & the various arachnids lineages.

Size : 4-ish cm of body length
Time period : Early Silurian
Paleoart speculativometer : Few missing details

The animal drawn looks like an eyeless assemblage of body segments with a granulated outer texture

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 27d

Chasmataspidid evolution is a fascinating topic yet still poorly understood, and many uncertainties remain on their origins and evolutionary trends And of course: the usual drawing feedback & some references, thank you for reading I’ll see you on the next #Cheliceratime! 4/4

Despite looking a lot like an eurypterid, O. ushakovi differs from them on several key features. The most obvious is the body segmentation, the thick 4-segmented buckler at the front half of the opisthosoma being unique to chasmataspidids. Another interesting one is the morphology of the paddle-like 5th legs, a gold example of convergent evolution since it looks similar in both groups despite being built differently. It most probably derived from a pincer-like appendage for chasmataspidids, while eurypterids evolved theirs from pointy legs.

Chasmataspidids are among the oldest groups of euchelicerates, and may have originated in shallow waters of the landmasses that ended forming today’s North America & Europe. This rather rare group has a sparse fossil record showing the replacement of the old horseshoe crab-like forms by more derived eurypterid-like forms through the Ordovician and Silurian, best guess being an ecological specialization allowing the group to last longer alongside other more successfull relatives. The group seems to disappear after the Devonian, never to be seen again. Their eurypterids relatives endured until the end of the Permian but in relictual freshwater forms. The low diversity of chasmataspidids may have been one of the reasons behind their extinction, making them too vulnerable to the ecological changes occurring during the Devonian.

The slide also comprise a timescale featuring the 2 major pools of chasmataspidids being stratigraphically isolated, complicating the understanding of the group's evolution

Is this paleoart accurate?
Did I put yellow & reddish colors on it just because its name is a reference to a communist revolution? You bet I did xD (but it looks cool nonetheless and it’s not an aberration).

The overall morphology is taken straight from Dunlop (2002), it’s the most detailed & up-to-date description available.

I could have extended a bit the paddle-like 5th legs, but I think it’s better to stay safe on this one.

REFERENCES

· Dunlop J.A., 2002. Arthropods from the Lower Devonian Severnaya Zemlya Formation of October Revolution Island (Russia). Geodiversitas 24(2), p. 349-379.

· Dunlop J.A. & Lamsdell J.C., 2017. Segmentation and tagmosis in Chelicerata. Arthropod Structure & Development 46, p. 395–418.

• Garwood R.J. & Dunlop J.A., 2023. Consensus and conflict in studies of chelicerate fossils and phylogeny. Arachnologische Mitteilungen: Arachnology Letters 66(1), p. 2-16.

• Lamsdell J.C., Gunderson G.O. & Meyer R.C., 2019. A common arthropod from the Late Ordovician Big Hill Lagerstätte (Michigan) reveals an unexpected ecological diversity within Chasmataspidida. BMC Evolutionary Biology 19(8), 24 pp.

· Naimark E., Sizov A., 2025. Three groups of arthropods (Chasmataspidida, Offacolidae (?), and Euthycarcinoidea) cohabited a tidal zone in the late Cambrian paleobasins (495–488 Ma) of Eastern Siberia, Journal of Asian Earth Sciences 289, article 106595.

· Selden P.A., Lamsdell J.C. & Liu Q., 2015. An unusual euchelicerate linking horseshoe crabs and eurypterids, from the Lower Devonian (Lochkovian) of Yunnan, China. Zoologica Scripta 44 p. 645–652.

· Voss B.D., 2024. The phylogeny of Chasmataspidida. Graduate Theses, Dissertations, and Problem Reports 12475 44 pp.

Colorado Plateau Geosystems Inc., 2026.
Global Series. In DeepTimeMaps. Online at https://deeptimemaps.com/map-lists-thumbnails/global-series/

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 27d

This chasmataspidid is among the most complete of the group, and provided numerous informations regarding chasmataspidids evolution and their links to eurypterids. #Cheliceratime 3/4

This species, thanks to its really good conservation, is among the most eurypterid-looking among chasmataspidids, and in fact helped to bridge some gaps between the 2 groups by showing several features weren’t specific to eurypterid, either having stemmed from a common ancestry or convergent evolution:

Paddle-like 5th legs
(convergence)

A metastome plate, possibly derived from the compressed first opisthosomal segment

pointy epimeras on the last opisthosomal segment, something way more common among eurypterids

Tubular reproductive appendage

Eurypterid-like operculum

Chasmataspidids sometimes look like a mosaic of eurypterid & horseshoe crab features, but are often retrieved closer to eurypterids: both orders share similar traits and have deep paleozoic origins, more than probably during the Late Cambrian considering how diverse & derived some eurypterids already were in the Ordovician and how chasmataspidid seemed to appear in the Late Cambrian. The links of both groups with freshwaters, as well as several possible land exaptations, make their study of certain importance in assessing chelicerate terrestrialization.

The slide also showcase a putative phylogeny proposed to reconcile paleontological & molecular data, in which eurypterids & chasmataspidids may be close to arachnopulmonates (spiders, scorpions, vinegaroons...)

Chasmatapidids inner phylogeny is in the process of being revised, so to be clear, the names in the cladogram below aren’t fully official yet and come from an available but unpublished master thesis that is the current most up-to-date work on the topic. The order is usually split into an older early paleozoic bunch of species looking more like horseshoe crabs, like Chasmataspis laurencii, and a younger group mainly known from more recent periods. This later lineage comprises numerous Ordovician to Devonian species, all exhibiting a more eurypterid-like body: smoother profiles (especially for the prosoma), large eyes positioned foreward and a last pair of legs modified into paddle, just like many derived genera of eurypterines developed during the Ordovician & Silurian.

The slide also showcase a phylogeny of chasmataspidids showing the split between more horseshoe crab-like lineages and more eurypterid-like ones, in which the diploaspidids belong

Octoberaspis ushakovi belongs to this later group, and is usually seen as a relative of the best known genus Diploaspis within the family Diploaspididae. It seems however that it was closer to other genera that could form all together a group called Octoberaspidinae, characterized by a more rigid front opisthosoma and ridges running on their prosomal carapace, some being noticeable on O. ushakovi when looking near its large lateral eyes. These latter chasmataspidids seem to have had a large distribution across North America & Europe, from brackish to fully marine setup.

The slide also showcase a phylogeny of diploaspidids showing Octoberaspis belonging to the sub-family octoberaspidinae, in which can be found too Heteroaspis, Nahlyostaspis, Loganamaraspis & Dvulikiaspis

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 27d

You know the drill, let's talk about its morphology, discovery & paleoenvironment first to meet this chasmataspidid, which is among the best known chasmataspidid species. #Cheliceratime 2/4

Octoberaspis ushakovi is a species of chasmataspidid that was named in 2002, found in Devonian rocks from the Severnaya Zemlya Formation, a Russian geological Formation of the October Revolution Island.

Its name is a reference to several influences. The ushakovi part is an homage to Georgi Ouchakov, an arctic explorer, while the october part of the genus’ name is derived from the October Revolution Island. This large island is one of the several Russian ones in the Arctic circle, and was named after the October’s Revolution of 1917, which overthrow the Russian ruling class and led to the birth of the USSR.

Octoberaspis ushakovi lived during the Early Devonian in the shallow waters of the paleocontinent of Siberia during the Early Lockovian stage 419/415 million years ago, not so long after the Silurian/Devonian boundary.

O. ushakovi lived in a rich ecosystem that comprised many aquatic vertebrates such as acanthodians and various armored jawless fishes groups (osteostracans, anaspids...), and several arthropods like ostracods and phyllocarids. The presence of plant debris suggests this environment wasn’t too far from the coast. Most of the known arthropods were discovered in oval-shaped nodules.

Octoberaspis ushakovi is a medium-sized chasmataspidid, reaching 3 to 4 cm in length for the largest specimens. Unlike other devonian chasmataspidid with short & boxy bodies, this animal looked a lot like an eurypterid. The prosoma looks like half of an ovale and bears 2 pairs of eyes in a pattern similar to eurypterids: a pair of large ones on the side, and 2 little ones in the middle of the carapace. The legs are short and pointy like those of eurypterids, the last one being flattened and possibly helping in swimming.

The opisthosoma shows the unique segmentation pattern of chasmataspidids: first a boxy mesosoma of 4 large segments (one of them being compressed under the prosoma while the remaining 3 are larger) sometimes called a buckler and with dense granulation on its sides. It’s followed by a thinner metasoma of 9 segments. The body ends with a small pointy telson preceded by a pretelsonic segment with spines, giving a fork-like look to the animal’s body end.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· 27d

What time is it? It’s #Cheliceratime ! For this entry we're talking about a russian chasmataspidid, Octoberaspis ushakovi ! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️🧵 #arthropod #devonian #paleoart #sciart #bugsky #invert 1/4

This medium size chasmataspidid is among the most derived species of its order. It was named in reference to the October Revolution Island, a large Russian island named after the 1917 October revolution in Russia that led to the rise of the USSR.

Size : 3 to 4-ish cm of body length
Time period : Late Cretaceous
Paleoart speculativometer : Few missing details

The animal drawn looks like an eurypterid with a body looking like a mix of a horseshoe crab at the front and shrimp at the back

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 10

And to conclude the post, some bits of phylogeny and possible paleoecology, with as always, the usual paleoart autofeedback and refs! Thank you for reading & I’ll see you on the next #Cheliceratime! 3/3

Geogarypus gorskii is a geogarypid, one of the most basal families of the garypoid superfamily. Like many others, this super-family is part of the iocheirates, a suborder of pseudoscorpions characterised by the presence of venom glands in the pedipalps’ claws. As for the geogarypids, they contain, as of mid-2026, 3 genera (1 extinct, 2 extant) with a fossil record going back at least to the Early Eocene Epoch. The family however has a long cryptic history, having diverged from other garypoids during Late Triassic.

The slide also showcases the phylogenetic position of the geogarypids, at the base of the garypoids, themselves as a whole being the sister group to more derived venomous pseudoscorpions such as the cheliferoids

Geogarypus is today one of the most widespread genus of pseudoscorpions, with numerous species distributed all around the world. Like all pseudoscorpions, they hunt on the ground small arthropods, smaller than them. Several species of garypoids have been observed tearing a small hole in the prey’s body, through which they inject enzymes liquifying the prey from the inside. They later absorb the digested contents, making them stand apart from several other pseudoscorpions that simply chew their food and rather a bit spider-like in their feeding habits.

Is this paleoart accurate ?
I think the colors may be a bit flat, but apart from that it’s straight up taken out of its original description!

The pustules really are the only thing that makes this species stand out among Geogarypus species, take them out and it looks like a random species of this genus.

I tried to respect as much as possible the setae arrangement of the pedipalps.

The end claws should be even smaller I think.

REFERENCES

· Benavides L.R., Cosgrove J.G., Harvey,M.S. & Giribet G., 2019. Phylogenomic interrogation resolves the backbone of the Pseudoscorpiones tree of life. Molecular Phylogenetics and Evolution 139, article 106509.

• Dunlop J.A. & Penney D., 2012. Fossil Arachnids. Monograph Series Vol.2, Siri Scientific Press. 192 pp.

· Henderickx, 2005. A new Geogarypus from Baltic amber (Pseudoscorpiones: Geogarypidae). Phegea 33(3), p. 87–92

• Penney D., 2020. Fossil Spiders in Baltic Amber: An annotated systematic catalogue. Siri Scientific Press, 150 pp & 42 planches.

• Weygoldt P., 1969. The biology of pseudoscorpions. Harvard University Press, Cambridge, Massachusetts, 145 pp.

Geogarypidae -World Pseudoscorpiones Catalog
https://wac.nmbe.ch/order/pseudoscorpiones/genera/47

The ICS international chronostratigraphic chart 2025. Episodes 2025. Online at https://stratigraphy.org/chart

Colorado Plateau Geosystems Inc., 2026.
Global Series. In DeepTimeMaps. Online at https://deeptimemaps.com/map-lists-thumbnails/global-series/

Dunlop J. A., Penney D. & Jekel D. 2023.
A summary list of fossil spiders and their relatives. In World Spider Catalog. Natural History Museum Bern, online at http://wsc.nmbe.ch, version 23.5.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 10

First, let's talk a bit about its discovery, morphology, paleoenvironment and by extension of course, of the baltic amber, one of the most important amber for our understanding of extinct cenozoic terrestrial arthropods. #Cheliceratime 2/3

Geogarypus gorskii is an extinct pseudoscorpion species from Baltic amber. This species was named in 2005, the “gorskii” part of its name being a nod to Andrzei Gorski, a Polish scientist who discovered the amber chunk containing this arachnid. It’s the third Geogarypus discovered in Baltic amber, its large size (among others) making it clearly distinct from the other 2 species previously known. It has also been reported from Ukraine in the Rovno amber.

Baltic Amber is one of the most important fossil resins on the planet, both in terms of economy, human history and science, having been exploited for centuries and being one of the most widespread ambers in fossil trades. Its name is linked to the fact it has been retrieved all around the Baltic Sea, the sea washing ashore amber chunks. Major amber localities include for example Kaliningrad (Russia) and the Polish coast.

The exact datation of the Baltic amber is... unclear to say the least. It has been known for a long time to be of Eocene origin, but due to the numerous out of context finds of amber bits, determining a precise age has been really complicated. It’s mostly assumed to be of Mid-Eocene age (50-45 million years more or less), with early and late occurences extending possibly to the Eocene’s temporal boundaries, indicating an extensive amber production source in Europe during the Eocene Epoch.

Back in the Eocene, Eastern Europe was covered by an extensive subtropical to warm temperate forest. The amber we found today originated from umbrella pines of the genus Sciadopitys, whose resin trapped small organisms, including arachnids. This fossilized resin has delivered an astonishing 3500+ number of fossil arthropod species, more than 550 of them being only spiders.

The only known specimen of Geogarypus gorskii is a well-preserved female & relatively large Geogarypus of 3-ish mm long. It exhibits a classic pseudoscorpion body plan, with pedipalps ending with 2 slender pincer claws, short chelicerae with silk opening and a mite-like compact body with a segmented opisthosoma. As for other Geogarypus, the opisthosoma is thick and there are 2 pairs of eyes at the front, but the most noticeable feature is the collection of granulated pustule-like structure on the pedipalps’ femurs.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 10

What time is it? It’s #Cheliceratime & #Fossilfriday! Today, a pseudoscorpion found in the Baltic amber, Geogarypus gorskii! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️ 🧵 #arachnid #baltic #pseudoscorpion #amber #paleoart #sciart #bugsky #invert

Found in a chunk of Baltic amber, this pseudoscorpion is one of the three species of Geogarypus known from Baltic amber. Its most singular feature is the collection of large pustule-like granules on its pedipalps.

Size : 3mm of body length
Time period : Mid-Eocene
Paleoart speculativometer : Almost a carbon copy

The animal drawn is a pseudoscorpion, an animal looking a bit like a mix of a mite body type with the pincers of a scorpion

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 8

What's worth noting about this species is its super endemic Seychelles' distribution & the fact it's an endangered species (+the usual drawing auto-feedback and refs) Thank you for reading & I’ll see you on the next #Cheliceratime! 3/3

Sternothyrus braueri has only been spotted off the African East Coast on a few islands of the Seychelles Archipelago, making it a super endemic species, only living in a small area. It’s a ground dwelling arthropod, wandering on sandy substrate and leaf litter of tropical coastal forests.

Due to the scarcity of observations, the life cycle of this species isn’t really clear.

This mite, due to its limited distribution, has been classified by the IUCN as an endangered species, facing possible extinction risk if environmental changes or human pressures become too much.

Sternothyrus braueri is only one of the many examples of why protecting islands’ biodiversity is extremely important for our understanding of life on earth. These fragile environments house species of unconventional evolutionary paths, sometimes acting as refugium for long gone extinct lineages on mainlands, and build unique ecosystems in which every species is tightly connected and that some people rely to live on. Any perturbation in such small and close systems can put at risk numerous other species, and these environments deserve all our consideration in the upcoming changes of the century.

Is this drawing accurate ?
It was a fun one to draw, basicaly a shinny ball with legs^^

For once I tried to do like a light reflection since the cuticle is smooth to the point of being often light reflective.

Pedipalps are often visible so I decided to add them.

I 100% took advantage of the gnathosoma’s hidden position to not draw it.

REFERENCES

· Klompen H., 2010. Holothyrids and ticks: new insights from larval morphology and DNA sequencing, with the description of a new species of Diplothyrus (Parasitiformes: Neothyridae). Acarologia 50, p. 269–285.

· Klompen H., Lekveishvili M. & Black W.C., 2007. Phylogeny of parasitiform mites (Acari) based on rRNA. Molecular Phylogenetics and Evolution 43, p. 936–951.

· Krantz G.W. & Walter D.E., 2009. A Manual of Acarology. 3° Edition, Texas Tech University Press, 816 pp.

· Lehtinen P.T., 1995. Revision of the Old World Holothyridae (Arachnida: Anactinotrichida: Holothyrina). Invertebrate Taxonomy 9(4), p. 767-826.

· Thon K., 1906. Die aussere Morphologie und die Systematik der Holothyriden. Zoologische Jahrbucher, Abteilung fur Systematik, Geographie und Biologie der Tiere 23, p. 677-724.

GBIF - Sternothyrus braueri
https://www.gbif.org/fr/species/6892344

INaturalist, 2026. Sternothyrus braueri. Online at https://www.inaturalist.org/taxa/432722-Sternothyrus-braueri

Gerlach J. 2014. Sternothyrus braueri. The IUCN Red List of Threatened Species 2014: e.T201466A2706730. Online at https://dx.doi.org/10.2305/IUCN.UK.2014-1.RLTS.T201466A2706730.en.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 8

You know the drill, let's talk about its morphology, phylogeny & a bit of naming history first to meet this holothyrid mite. #Cheliceratime 2/3

Sternothyrus braueri is a species of free living wandering notably large parasitiform mite, reaching between 6 and 7 mm in main body length depending on if you’re looking at a male or a female respectively. Despite its odd look of a shiny ball with legs, it exhibits a classical mite body plan with minor particularities:

A fused prosoma & opisthosoma, forming a large oval-shaped idiosoma that bears the walking legs. The dorsal side is unified in a smooth hard shield called scutum.

The animal is blind, lacking any eyes.

4 pairs of walking legs, longer than the main body and covered with short & sparse setae. The first pair’s last segment bears brighter setae, ending in a white-like leg tip.

The smooth scutum is the most remarkable body structure of the animal, and is almost deprived of any hairy areas. Despite not being especially visible, this mite does possess a gnathosoma bearing chelicerae & pedipalps, but it’s folded under its body, hiding the genital opening. Like ticks, its first pair of legs has a Haller’s organ on its tarsus, a lil’pit allowing the animal to catch on chemical signals from its surroundings. The species is well represented thanks to numerous male & female specimens, and has been spotted on the field by naturalists outside of research campaigns.

Sternothyrus braueri belongs to the holothyrids, an order of free living parasitiform mites often recovered as the closest relatives of ticks. They all share a heavily sclerotinized hard exoskeleton making them look like lil’ shiny balls with 8 legs. All members of this group are distributed on landmasses derived from the ancient Gondwana supercontinent, suggesting a Southern Pangean origin concordant with the hypothesized geographical origin of ticks, both groups having potentially evolved from a common ancestor in South Pangea in Late Paleozoic. Modern holothyrids are divided into 3 families, S. braueri belonging to the old world’s family Holothyridae.

The slide also comprises a phylogenetic tree of parasitiforms in which holothyrids are made of 3 families and is the sister group to ticks

Sternothyrus braueri was at first named “Holothyrus braueri” in honor of Friedrich Brauer, an Austrian entomologist. It was housed under the genus Holothyrus when it was first described in 1905. It gained its current name and own genus in a 1995' revision of holothyrids, which argued for this split on the basis of numerous plesiomorphic (ancestral/primitive) features when compared to other species belonging to the Holothyridae, especially in the morphology of the chelicerae and in the setae arrangements on several body parts.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 8

What time is it? It’s #Cheliceratime ! For this entry I'd like to talk about Sternothyrus braueri, a large mite endemic to the Seychelles! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️🧵 #mite #arachnid #seychelles #sciart #bugsky #invert 1/3

This ground-based arachnid is a distant relative of ticks. With its hard cuticle, it’s an endangered species only known from the Seychelles archipelago.

Size: 6mm of body length
Time period: Holocene (present day)
Conservation status: Endangered

The animal drawn is a reddish mite with a ball-shaped body and 8 walking legs

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 3

Mites have a complicated relationship with their own fossil record when it comes to phylogeny, and species such as this one are of great interest (+the usual drawing autofeedback and some refs) Thank you for reading & I’ll see you on the next #Cheliceratime! 3/3

Gehypochthonimimus hibernicus features makes it for now the oldest species of gehypochthoniids, a family of parhyposomates, one of the main sub-divisions of oribatid mites. Researchers did mention the possibility of this species belonging to an unknown extinct family, but chose the safest option by putting it in a known lineage with matching features.

The slide also comprises a phylogenetic tree of acariform mites in which gehypochthoniids are one of the several lineages of oribatids from the sarcoptiformes.

Although being one of the most important land animals and being crucial in every land environment’s equilibrium, mites have quite a uneven fossil record depending on the time period and way to be preserved. Most of the named extinct species come from amber deposits (Cretaceous to modern day) and belong to already well identifiable lineages, while their early evolution is barely known from fossil remains. Such discoveries as Gehypochthonimimus hibernicus are important because, even if they are too incomplete & way too few to properly study paleozoic mites with as much details as modern species, give some calibration points to estimate when groups appeared or split off from one another.

Is this paleoart accurate ?
To my knowledge it’s the first paleoart of this species, so I tried my best! It’s mostly based on Gehypochthonius but stretched to fit the right proportions since the fossil lacks a lot of precise features.

I kept the gut contents since they appear clearly on the fossil and can be well-visible in modern mites in transparency.

The mouthparts and setae are a mix of fossil and modern features.

The legs are taken straight from modern Gehypochthonius species.

REFERENCES

• Dunlop J.A. & Penney D., 2012. Fossil Arachnids. Monograph Series Vol.2, Siri Scientific Press. 192 pp.

· Klimov P.B., OConnor B.M., Chetverikov P.E., Bolton S.J., Pepato A.R., Mortazavi A.L., Tolstikov A.V., Bauchan G.R. & Ochoa R., 2018. Comprehensive phylogeny of acariform mites (Acariformes) provides insights on the origin of the four-legged mites (Eriophyoidea), a long branch. Molecular Phylogenetics and Evolution 119, p. 105-117,

· Krantz G.W. & Walter D.E., 2009. A Manual of Acarology. 3° Edition, Texas Tech University Press, 816 pp.

• Sharma P.P. & Gavish-Regev E., 2025. The Evolutionary Biology of Chelicerata. Annual Review of Entomology 70, p. 143–163.

· Subías L. & Arillo A., 2002. Oribatid mite fossils from the Upper Devonian of South Mountain, New York and the Lower Carboniferous of County Antrim, North Ireland (Acari, Oribatida). Estudios del Museo de Ciencias Naturales de Alava 17, p. 93-106.

The ICS international chronostratigraphic chart 2025. Episodes 2025. Online at https://stratigraphy.org/chart

Colorado Plateau Geosystems Inc., 2023. North America. In DeepTimeMaps. Online at https://deeptimemaps.com/map-lists-thumbnails/global-series/

Dunlop J. A., Penney D. & Jekel D. 2023. A summary list of fossil spiders and their relatives. In World Spider Catalog. Natural History Museum Bern, online at http://wsc.nmbe.ch, version 23.5.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 3

First, when & where did this mite live, what its fossils look like, and a few things about the history of how it was named. #Cheliceratime 2/3

Gehypochthonimimus hibernicus is one of the several extinct mites’ species that were named in 2002 from carboniferous deposits found on the sea shore of Fair Head, a Cliff of the County Antrim in Northern Ireland.

This species’ name is a blend of several topics related to the animal. The genus name refers to the current mite Gehypochthonius, supposed to be a distant relative of the fossilised mite. The species epithet hibernicus is derived from Hibernia, which was how Ireland was called in Latin under the Roman Empire.

The precise age of this arthropod is uncertain, even tho it’s mostly assumed to be of Eraly to Mid-Carboniferous thanks to general stratigraphy, with an age around 335 to 330 million years ago. Back in that time, Ireland was just below the equator, in the middle of the convergence of landmasses that were joining to make Pangea. This situation produced numerous volcanoes along these areas, like the one that made the rocks whose reworking made the sediments in which a root fossilized, encapsulating the only known specimen of Gehypochthonimimus hibernicus.

G. hibernicus was far from being the only arachnid in this environment, as remains of stem spiders & stem amblypygids, scorpions & trigonotarbids are mentioned in its original description. Several other mite species are also known from this locality, all being oribatids.

Gehypochthonimimus hibernicus is a small mite of only 430 µm with an ovate potato-shaped body. Like all oribatid mites, it possesses a domed shield and long, branched/pectinate setae on its back. Although some features are missing, the setae coverage & morphology are surprisingly close to an extant mite genus called Gehypochthonius, also sharing a similar body and weak sclerotinization of the exoskeleton, making the animal a bit transparent. Obvious and rare enough to be noted for a fossil mite in rocks, the specimen kept some gut content well visible.

As you noticed, the fossil is far from complete, the mouthparts & tips of the legs being for example unknown. The specimen was recovered after chemical treatment of the rocks, in this case dissolution in hydrofluoric acid, a technique that may seem impressive but which is pretty efficient to isolate small & highly resistant organic material. It’s most often used for seeds & pollens (and 3 spores are attached on this mite for example) but sometimes it’s also used with a lot of precaution on bones & exoskeletons too.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 3

What time is it? It’s #Cheliceratime & #FossilFriday! Today's entry is our first oribatid mite! It's also to my knowledge this species' first paleoart! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️🧵 #mite #arachnid #paleoart #bugsky #invert 1/3

This extinct mite is among the oldest named oribatids. It was discovered in carboniferous rocks from Northern Ireland, hence its name since Ireland is called Hibernia in Latin.

Size : 430 µm
Time period : Early Carboniferous
Paleoart speculativometer : Mostly based on another taxon

The animal drawn is a yellow mite with long setae on its back

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 1

This species is a good example of dimorphism among harvestmen, even between males (+the usual drawing auto-feedback and refs) Thank you for reading & I’ll see you on the next #Cheliceratime! 3/3

One interesting thing about this species is how sexual dimorphism manifests depending on which individual you’re looking at. Not all males are the same, as some of them, those with the long chelicerae, are what’s called “major males”. On the other end of the male’s population, others lack such features and look a lot more like females, making them being called “minor males”. Such situation is also known among other species like insects, leading to some slight differences in how males can interact and reproduce (it’s a bit out of the topic but for those of you who watched Prehistoric Planet, that’s exactly what’s portrayed in some pterosaurs in Season 1 Episode 3).

Is this drawing accurate ?
I think it looks cool, I did of course a major male since they are the ones with the most noticeable features.

I think I did the chelicerae a bit too raised up for a live specimen position.

The tarsus may be a bit short tbh.

Yup, this bending is weird, I was out of place on the sheet :’)

REFERENCES

• Derkarabetian S., Lord A., Angier K., Frigyik E. & Giribet G., 2023. An Opiliones-specific ultraconserved element probe set with a near-complete family-level phylogeny. Molecular Phylogenetics and Evolution 187, article 107887.

· Pinto-da-Rocha R., Macado G. & Giribet G., 2007. HARVESTMEN: The Biology of Opiliones. Harvard University Press, Cambridge, Massachusetts & Londres, England. 597 pp.

• Taylor C. & Hunt G., 2009. New Genus Of Megalopsalidinae (Arachnida: Opiliones: Monoscutidae) From North-Eastern Australia. Zootaxa 2130, p. 41-59.

INaturalist, 2026. Neopantopsalis pentheter. Online at https://www.inaturalist.org/taxa/527409-Neopantopsalis-pentheter

Kury A.B., Mendes A.C., Cardoso L., Kury M.S., Granado A., Giribet G., Cruz-López J.A., Longhorn S.J., Medrano M., Oliveira A.B.R., Kury I.S. & Souza-Kury M.A., 2024. World Catalogue of Opiliones. WCO-Lite version 2.7. Online at: https://wcolite.com/.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 1

You know the drill, let's talk about its morphology, distribution & phylogeny first to meet this harvestman. #Cheliceratime 2/3

Neopantopsalis pentheter is a medium-sized species of harvestman, with a main body length of around 5 mm. Apart from the ridiculously long chelicerae of some specimens that we’ll talk about in the next slide, it exhibits a classical harvestman body plan:

An overall dark coloration with bits of lighter colors (here yellow).

An ovate compact body with a blurry distinction between the prosoma & opisthosoma at first glance.

2 eyes in the middle of the scutum’s front part sitting on a raised bump called “ocularium”.

4 pairs of extremely long & thin 7-segmented walking legs. The first legs bear spines on their first segment.

One interesting thing about this species is how sexual dimorphism manifests depending on which individual you’re looking at. As it’s often the case among harvestmen, females tend to lack complex additional structures, while males have enlarged attributes like hard projections on their appendages, spines or horn-like structures on their bodies.

And you guessed it, in present case this manifests with some males having extremely long chelicerae, longer than the harvestman’s main body. This feature is shared by several close species, and all the species of the Neopantopsalis genus (N. quasimodo, N. pentheter, N. psile...) have males possessing such elongated appendages.

This species has been recovered from Eastern Australia, in Queensland & New South Wales. This harvestman lives across the hot temperate rainforest spanning over Australia’s East coastal areas.

Due to the scarcity of observations, the life cycle of this species isn’t really clear.

Neopantopsalis pentheter belongs to the family Neopilionidae, one of the families part of the eupnoi suborder of harvestmen. This group contains several other species with elongated chelicerae, as male harvestmen often are the ones with extravagant features. Neopilionids are a good case of how much harvestmen biogeography dictated these arachnids’ evolution, this family being distributed on southern landmasses such as Australia, Tasmania, New Zealand, South America & Southern Africa, revealing a possible gondwanan origin deep in the past.

The slide also showcase a phylogenetic tree on harvestmen in which Neopilionidae is the sister group to the most derived families of the eupnoi sub-order.

Amypteride🏳️‍⚧️🔻🕷🦂@amypteride· Jul 1

What time is it? It’s #Cheliceratime! Today, a harvestman with super long chelicerae, Neopantopsalis pentheter ! All the basic infos are here but if you want to learn more, there’s more in the thread below!⬇️🧵 #harvestman #arachnid #australia #sciart #bugsky #invert 1/3