Shocked to see some artists saying that using ai slop as reference is ok. It's really fucking not. Not only are you still using the mashed-up uncredited work of the rest of us artists, but it degrades your whole visual library because it hallucinates. If you do this I do not respect you

if you care about trans people, do not watch the new jk rowling show. don’t even hate watch it or you will be funding this new intentionally transphobic organization. we cannot allow hateful people take away more of our rights

Thank you so much for your kind words ! (And happy to help ah ah !^^)

Love those types of resources. Labour of love, very useful and rich with knowledge. Saving for our taxonomy key training modules. 💙🦂🧐

🧪 🌏

this is so super great for writers and artists, also scifi/fantasy. Get those bug parts right!

Thank you for the repost !^^

Le fait que Macron et ses sbires gouvernementaux n’aient pas le moindre mot pour dénoncer les éructations racistes visant des
maires insoumis sur la chaîne dite "d’info" d’extrême droite du groupe Bolloré doit être regardé pour ce qu’il est: un consentement - et donc un encouragement.

A QUICK VISUAL TOUR OF CHELICERATES’ ANATOMIES Chelicerates’ morphologies are widely variable: from spiders to horseshoe crabs or mites & scorpions, it can be hard to navigate, even more so with the numerous words used to describe these animals’ body parts. This post aims to serve as a simplified tool for you to better understand Cheliceratime’s entries by summarizing the main information about each large chelicerate groups, so don’t forget to swipe if you’re looking for a group in particular!

What time is it? It’s #Cheliceratime !
This post aims to serve as a simplified tool for you to better understand Cheliceratime’s entries by summarizing the main information about each large chelicerate groups, so unroll the thread to find the group you're looking for!⬇️ 🧵

#sciart #arachnid
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Trigonotarbida Forwarded clypeus hiding the chelicerae 2 median eyes & little pairs on the sides Complex dorsal lock between the prosoma & the narrowed 1° opisthosomal segment Last 10, 11 & 12 segments folded on the underside, the last to in a sort of “postabdomen” Ventral sac 2 pairs of book lungs 3 claws: 2 large ones & a smaller one Last segment of the chelicera turned into a fang Trilobed opisthosoma with Lateral Lobe/Plate & Median Lobe/Plate

Araneae (spiders) Group represented: Araneomorphs Last segment of the chelicera turned into a venomous fang Palpal bulbs for reproduction in males Primitively 8 eyes in 2 rows, but eye pattern highly variable Fovea Patella often shorter than Femur & Tibia No muscles to extend the legs, extension is done by self-regulation of internal hydraulic pressure 2 claws by default, 3 among web-spinning species Opisthosoma often without external segmentation 2 to 6 spinnerets from which silk is spinned Book lungs (1 pair in araneomorphs, 2 in tarantulas & mesotheles) Tracheae (absent in tarantulas & mesotheles) Epygine (female genital opening) Narrow pedicel (“wasp waist”) Sternum Labium Endite (extension of the pedipalp’ coxae to process food) Notes: Spiders are highly diverse, this is an overall generalised body plan. Uraraneids and other stem spiders lineages are based on the same general model but with sometimes a flagellum and doubts about the presence of true spinnerets

Pedipalpi (Vinegaroons, schizomids & amblypygids/”whip spiders”) 2 median eyes in & little lateral pairs for species with sight Prosoma in one block for vinegaroons & amblypygids, subdivided like solifuges & palpigrades for schizomids Last 3 segments of the opisthosoma are smaller & forming a postabdomen Telson mondified into a flagellum (lost in amblypigids & reduced in schizomids) 2 pairs of book lungs (only one in schizomids) Tarsus is always subdivided into tarsomeres First pair of legs elongated and used as antennae, loss of their walking function Large raptorial pedipalps Note: This diagram is a mix of both schizomids, vinegaroons & amblypygids to show the numerous features shared by these 3 orders despite their differences.

And for the end of the thread, the pantetrapulmonates: trigonotarbida, araneae (spiders) and pedipalpi (vinegaroons, amblypygids, schizomids)

Thank you for reading & I’ll see you on the next #Cheliceratime!

#arachnid #spider #trigonotarbid #vinegaroon #amblypygid #schizomid
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Ricinulei Group represented: Neoricinuleids Forwarded cucullus hiding the chelicerae 2-segmented small chelicerae Carapace densely granulated Males’ 2° femur enlarged Double trochanter (3° & 4° pairs of walking legs) Complex dorsal lock between the prosoma & the narrowed 1° opisthosomal segment Trilobed opisthosoma with Lateral Lobe/Plate & Median Lobe/Plate Last 3 segments of the opisthosoma form a short postabdomen Pedipalps ending with a small pincer claw Males’ 3° legs modified for reproduction Tracheal openings hidden among the legs Pedipalp folded under the body & ending with a pincer claw

Phalangiotarbida Genus represented: Mesotarbus Small leg-like pedipalps Extremely small chelicerae, exact morphology unsure 6 eyes arranged in 3 pairs on a trifoliate tubercle First 6 segments of the opisthosoma are densely packed on the dorsal side Broad 3-segment end of opisthosoma (often fused) Dorsal anal opening Ogive-shaped main body Crab-like heavy walking legs 1 pair of spiracled linked to unknown respiratory organs reproductive’s morphology unknown Note: This group is still poorly known; further research could change several details radically.

Pseudoscorpiones Group represented: Cheliferoids Pedipalps turned into pincer claws (with venomous glands in iocheirates species) Small 2-segmented chelicerae with a small spinneret called “galea” on the moveable digit linked to a silk gland 0 to 4 simple eyes on the forward rims of prosoma Patella usually is longer than the femur Exoskeleton can be heavily ornamented with tubercles Opisthosoma ending by an anal cone, no telson 2 pairs of tracheae Large genital plate First opisthosomal segment non-visible on ventral side Endite (extension of the pedipalp’ coxae to process food)

Scorpiones Group represented: Orthosternians Pedipalps turned into pincer claws 2 median eyes in & little lateral pairs Legs telescoped backwards Legs’ coxae well-developed & forming a stomotheca (a pre-oral chamber before the mouth) Sternum Genital opening & Pectines (ventral sensory appendages close to the ground) closely grouped 4 pairs of book lungs Opisthosoma subdivided into a mesosoma of 7 segments & a metasoma (=”tail”) of 5 segments Telson turned into a venomous sting Acculeus (sting) Vesicle (contains the venom) Note: Scorpions changed a lot since the Silurian, many of the paleozoic species didn’t have stomotheca for example. This diagram is mostly representative of today’s species.

Orders of unclear affinities & scorpion-like figures: ricinulei, phalangiotarbida, pseudoscorpiones and scorpiones

#Cheliceratime #arachnid #ricinulei #phalangiotarbida #pseudoscorpion #scorpion
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Opiliones (Harvestmen) Large chelicerae useful for identification Leg-like pedipalps of various morphologies, useful for identification Odoriferous gland for defense pruposes 2 median eyes sitting on an ocularium Prosoma & opisthosoma broadly joined, often merged together Dorsal side often covered by a +/- long scutum (shield) Legs often elongated, with tarsus split in numerous tarsomeres (up to 100) Anus often can be way more forward than in other arachnids Genital opening thrust forward between the legs and also bears the tracheal respiratory system Legs’ coxae well-developed & forming a stomotheca (a pre-oral chamber before the mouth) Note: Harvestmen show a wide diversity of morphologies concerning the prosoma-opisthosoma fusion and their ventral side, so the one here doesn’t exist & is a fusion of several types to reflect the broad average of what you can find among these arthropods.

Palpigradi Large projected forward chelicerae No eyes, presence of specific sensory organs at the body front (called “frontal organ” & “lateral organ”) Prosomal carapace subdivided from front to back into: propeltidium, mesopeltidium, metapeltidium Last pair of legs 8-segmented Last 3 segments of the opisthosoma smaller & forming a postabdomen Telson modified into a flagellum of 15-ish segments, can easily break Ventral sacs (if Eukoeneniidae, absent in Prokoeneniidae). No external respiratory system, the animal is small enough for gas exchanges to occur through the weakly sclerotinized exoskeleton Genital plate extending backward Long pedipalps, used for walking, retention of 3 claws at the appendage’s end The first pair of legs is 12-segmented and mainly used as sensory appendages while walking

Solifugae 2-segmented super enlarged chelicerae 2 median eyes on a high spot Prosomal carapace subdivided from front to back into: propeltidium (larger & raised), mesopeltidium, metapeltidium Patella is usually longer than the femur Tarsus divided into tarsomeres, usually 3 tarsomeres but sometimes more (like 6 among solpugids) Double trochanter on the 3° & 4° walking legs Soft 10-segmented opisthosoma 3 pairs of tracheal openings on the underside of the opisthosoma malleoli/racquet organs on the coxae & trochanter of the last pair of legs, acting as sensitive organs close to the ground 1 pair of tracheal openings between the 2° & 3° walking legs First pair of walking legs significantly shorter than pedipalps Long & strong leg-like pedipalps, covered with highly sensitive setae Adhesive organ at pedipalps’ tip

The mite body plan Although not forming a single monophyletic group and having a morphological diversity way too vast to be exhaustively synthesised in a single drawing, all chelicerates called “mites”, from flour mites to ticks, share a broad body plan easily recognizable, even tho there are many variations depending on which group you’re looking at. The prosoma’s part bearing chelicerae & pedipalps is detached from the body and is called “gnathosoma” Prosoma & opisthosoma fused, forming a new body part called “idiosoma”. Some groups have dorsal shields. The front half bearing the first 2 pairs of legs is called “propodosoma”, and the back half “hysterosoma) Small eyes can be present, most often on the idiosoma forward sides Legs’ segment count is HIGHLY variable depending on the considered group Anal plate Genito-ventral plate Breathing through tracheae if present (openings usually directed to the front half of the body) Legs’ coxae can be fused to the idiosoma in some groups Caruncle/ Pre-tarsus Sternal plate

Some apulmonate arachnids: Opiliones (Harvestmen), Palpigradi, Solifugae and the mite body plan

#Cheliceratime #arachnid #harvestmen #solifuge #palpigrade #mite #tick
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Xiphosura (Horseshoe crabs) Group represented: Limulines Cardiac lobe extending forward Ophthalmic ridge The first & second segments of the opisthosoma are functionally linked to the prosoma, making horseshoe crabs the sole chelicerates where using the word “cephalothorax” is 100% correct scientifically. The rest of the opisthosoma is called “thoracetron” More rigid thoracetron with fused segments for all post-Paleozoic species Thoracetron sides often spiny, modern species having articulated spines Sword-shaped telson with wide motion range 5 pairs of book gills. They can be flapped to aid in swimming on the back when needed First opisthosomal legs reduced to non-functional appendages stuck between prosomal walking legs & called “chilaria” Large genital operculum at the end of the cephalothorax Last prosomal legs modified & called “pusher legs”, with a small highly modified exopodite serving as a cleaning structure. 4 first walking legs ending with pincer claws Uniramous prosomal appendages covered by the vaulted prosomal shield 3-segmented chelicerae

Chasmataspidida Group represented: Diploaspidids lineage 5 pairs of uniramous only-walking prosomal legs Unknown chelicerae, supposed to be small & 3-segmented Last segment of 5° legs modified into a small claw or a leg joint Opisthosoma subdidived into typical pattern of a shorter & broader mesosoma of 4 segments, and a longer narrower metasoma (=tail) of 9 segments. The 3 largest segments of the mesosoma are grouped under the term of “buckler”. Reduced pointy/rounded telson Genital appendage tubular and stemming from the 2° operculum, similar to what’s seen in eurypterids Respiratory organs hidden under 3 opercula and of unknown morphology, probably book gills like horseshoe crabs & eurypterids. Possibly 3 supplementary operculas on the first 3 segments of the metasoma. First opisthosomal segment super reduced and squished against the prosoma, overlapping in ventral view on the prosoma in the form of a metastoma between the 5° legs.

Eurypterida ("sea scorpions") Group represented: Derived eurypterines Chelicerae small on average, rarely visible beyond the prosomal rim in most species Large lateral eyes with excellent sight Morphologies of prosoma & uniramous legs are extremely diverse, key features for eurypterid identification & classification Eurypterines specifically have an additional segment to their 5° legs, and the said legs are modified in most eurypterines into large flippers aiding in swimming Opisthosoma subdidived into typical pattern of a broader mesosoma of 6 segments, and a narrower metasoma (=tail) of 6 segments. Sometimes a 7/5 preabdomen/postabdomen denomination is used Telson of various shapes depending on the group considered Complex & segmented tubular +/- long genital appendage called “zipfel” and steming from the fused 1° & 2° operculum. 5 pairs of book gills hidden under opercula called “blattfüsse” First opisthosomal segment squished against the prosoma, only lasting as an overlapping metastoma between the 5° legs in ventral view 1° & 2° opercula fused, ensuring both reproduction & respiration

The arachnid body plan Due to multiple terrestrialization events, arachnids in their traditional sense aren’t monophyletic and therefore, didn’t originate from a single terrestrial ancestor. However, the historic grouping of these animals in a single class relied on a lot of morphological similarities that seem to be convergently shared by default by all terrestrial euchelicerates. The mouth is pushed forward to accommodate the changes in food processing between land & water The first pair of legs is modified as manipulatory & sensory appendages, now called pedipalps Shortened chelicerae, often only 2-segmented 0 to 8 eyes, pattern highly variable Prosoma-opisthosoma connexion is often less rigid and can be morphologically diverse Opisthosoma made of max 12 segments, the ancestral first one being lost Telson reduced, most frequently lost, or turned into a flagellum Spiracles (air-breathing openings) usually on the ventral first half of the opisthosoma, internal respiratory system Genital opening often in the shape of a plate Prosoma’s ventral side often shows fused plates, rigidifying the body for terrestrial walk Loss of the gnathobases & reduction of the masticatory role of the coxae, the legs mainly serve to move Uniramous appendages

Aquatic main euchclicerates groups: Xiphosura (Horseshoe crabs), Chasmataspidida, Eurypterida & the arachnid body plan

#Cheliceratime #horseshoecrab #chasmataspidid #eurypterid #seascorpion #arachnid
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Nomenclature & legends To make them easier to understand, all diagrams will have the same color coding, helping with identifying which body parts are the same across chelicerates’ diversity. MAIN BODY Euchelicerates : Prosoma-opisthosoma-telson Pycnogonids: cephalosome-thorax-abdomen (+telson for some fossils) The genital opening/external organs will be indicated in pink, and the breathing system will be in white. APPENDAGES The first arthropods had double legs called “biramous legs”, with 2 branches attached to a single coxa (trilobites are a good example of this condition). The endopodite, the more inward one, was used for walking, while the exopodite, the more outward one, served mostly for respiration. Most chelicerates conserved only one of them, more often to walk, and heavily modified the breathing ones. Chelicera, Birmous legs made of endopodite (walking) & endopodite both attached to a coxa, and other significant appendages are in purple. Leg’s segments name abreviations Cx: Coxae Tr: Trochanter Fe: Femur Pa: Patella Ti: Tibia Mt: Metatarsus Ta: Tarsus Pr: Propod

Chelicerata No one knows for sure what the ancestral chelicerate looked like, the group as a whole being really rare before many of its main lineages became well established in the fossil record (and already too different from one another). The diagram here is an attempt to summarize the common traits of all chelicerates on a theoretical profile reminiscing of a cambrian habellian-like arthropod. Front appendages are chelicerae, claws (or later fangs) made of 4 or more segments at the beginning (now reduced to 3 or 2 in all current chelicerates) Accute senses with a well- developed nervous system, eyes and numerous setae (=hairs) sensing vibrations No clear distinction at first of anterior & posterior tagma. At least the first 4 segments (acron+3 first legs-bearing segments) were already fused together, & generally the front of the body is more dedicated to walking & handling food, while the body end is often non-walking. The exact number of body segments is unknown, most chelicerates (except pycnogonids) having ancestraly around at least 15 segments post-chelicerae. The mouth opening is located between the chelicerae & the first pair of legs Gnathobase (serrated extension of the pedipalp’ coxae to process food, lost in pycnogonids & terrestrial forms) Ancestral forms have biramous legs with a walking endopodite & a breathing exopodite. Endopodites become more and more reduced past the front part of the animal, and quasi all living chelicerates have lost the biramous state for uniramous legs. Segmented body covered by an unmineralized exoskeleton made of chitine, growing through molting. Body ending with an accessory telson, located after the anal opening.

Pycnogonida (sea spiders) Group represented: Pantopods, family Nymphonidae Body in 3 tagma: cephalosome, thorax & abdomen Mouth proned forward in a proboscis 1° walking legs on the cephalosome 4 eyes on an ocular tubercle Legs host part of the digestive tract and their large surface serve for breathing Thorax bearing 2°, 3° & 4° pairs of walking legs Small abdomen, almost non-existent to absent in modern species Long, 9-segmented legs with tripled coxae, attached to the main body by a lateral process Gonopores (reproductive openings) on the 2° legs 3° appendages used only for handling eggs, called ovigers 2° appendages used for manipulation, called palps Notes: Paleozoic pycnogonids are extremely diverse morphologically, often exhibiting a more developed abdomen & more primitive appendages structure. Larvae morphology is also typical and is called “protonymphon”

Euchelicerata 3-segmented chelicerae Primitively 2 simple median eyes (ocelli) & 2 lateral compound eyes Often show a raised median part on the prosoma called cardiac lobe, corresponding to vascular & nervous system clustering Body divided into a prosoma & an opisthosoma, often called respectively “cephalothorax” & “abdomen” in popular science 13-segmented opisthosoma, mostly dedicated to hosting non-locomotory & non-sensitive systems. Most derived groups only show 12 segments or less, the first segment being often reduced or squished into the prosoma in modern groups. Pointy telson Exopodite modified into a booked structure to grant more surface for gas exchanges for respiration, similar to simpler horseshoe crab’s book gills All extant euchelicerates have their genital opening placed on their 2° opisthosomal segment, which was in third position before being reduced or squished into the prosoma in modern groups First opisthosomal segment with a pair of walking legs, reduced to non-functional appendages or just absent in most euchelicerates Prosoma bearing chelicerae & 5 pairs of walking legs. Endopodites reduced (if not absent in most cases, most euchelicerates having uniramous prosomal legs) Mouth placed more at the center of the prosoma Note: This diagram doesn’t represent a specific group but illustrates the template from which horseshoe crabs, eurypterids, chasmataspidids & arachnids evolved. The overall shape is inspired by species of synziphosurines.

Some info about drawings' legends, and here we go, we begin with chelicerata, pycnogonida & euchelicerata

#Cheliceratime #chelicerata #pycnogonida #seaspider #anatomy
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A QUICK VISUAL TOUR OF CHELICERATES’ ANATOMIES Chelicerates’ morphologies are widely variable: from spiders to horseshoe crabs or mites & scorpions, it can be hard to navigate, even more so with the numerous words used to describe these animals’ body parts. This post aims to serve as a simplified tool for you to better understand Cheliceratime’s entries by summarizing the main information about each large chelicerate groups, so don’t forget to swipe if you’re looking for a group in particular!

What time is it? It’s #Cheliceratime !
This post aims to serve as a simplified tool for you to better understand Cheliceratime’s entries by summarizing the main information about each large chelicerate groups, so unroll the thread to find the group you're looking for!⬇️ 🧵

#sciart #arachnid
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Corneille sur une pelouse à pâquerettes, présentant son bec de profil. Elle a l'air doux.

Alice vous informe que c'est le week-end

Petit rappel par rapport aux tests de féminité: les 9 dernière femmes qui ont échoué au test de féminité étaient toutes des femmes cis.
Elles ont dû subir une inspection des organes génitaux de leurs poils pubiens et de leurs seins pour ça.
Certaines ont tenté de se suicider par la suite.

Artists, never forget that you are not a brand. You do not need to be consistent and marketable. If you CHOOSE to strive for these things that’s fine, but you do not NEED them. You are a fucking person, multi-faceted and complex. People who do not respect that see your art as a product

Je sais qu'on a pas beaucoup de bonnes nouvelles en ce moment mais des fois y'a des trucs cools comme ça qui donnent le smile

This is a drawing of multiple pink arthropods on a light pink background. In the middle of this drawing there's a text "pink bug club". Each arthropod is labeled with their scientific name. Bugs shown are: gyponana gladia, phromnia rosea, asphaera quadrifasciata, cheilomenes aurora and cheilomenes bidentata,thomisus onustus, microphotus angustus, cubaris cherry blossom, dryocampa runicunda (aka rosy maple moth), hymenopus coronatus (aka orchid mantis),aedophron rhodites,cithaerias aurorina snd brachycybe rosea

I know beauty exists because bugs are so full of it💞
.
#bugs #myart #arthropods #biology #art

screenshot of a resignation letter expressing sadness at leaving NASA

My resignation letter

What time is it? It’s #Cheliceratime !
No particular species today, we're doing a bit of a recap before going further: in the end, what is a chelicerate?

Answers in the thread below! ⬇️ 🧵

#arthropod #scicom #arachnid #horseshoecrab #pycnogonid #eurypterid #invert #bugsky

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Chelicerates & humans Human’s perception of chelicerates is... complicated. Arachnids (and especially spider-looking ones) are often subjects to arachnophobia, and the disconnection between humans and chelicerates often makes it hard for many people to sympathize with them. They are also harvested economically to the point of risking extinction, like for horseshoe crabs & many spiders. However, of the more than a hundred thousand species, very few pose a threat to humans, and we still know little of their behaviors for many species. Whether we like it or not, they are a vital part of Earth’s ecosystems, spiders’ regulation of insects making them the most important predators for land ecosystems. Most of these views are tied to our link with nature and how we perceive it, arachnids being typically non-charismatic animals for numerous people. And I hope your time on these posts will help you see them from a new perspective, not as monsters, but incredibly diverse & fascinating animals :)

REFERENCES (part 1) · Aria C. & Caron J.-B., 2019. A middle Cambrian arthropod with chelicerae and proto-book gills. Nature 573, p. 586–589. · 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. • Bicknell R.D.C. & Pates S., 2020. Pictorial Atlas of Fossil and Extant Horseshoe Crabs, With Focus on Xiphosurida. Frontiers in Earth Science 8, Article 98, 60 pp. • Cloudsley-Thompson J.L., 1977. Adaptational biology of Solifugae (Solpugida). Bulletin of the British Arachnological Society 4, p. 61-71. · Clouse R.M et al., 2017. First global molecular phylogeny and biogeographical analysis of two arachnid orders (Schizomida and Uropygi) supports a tropical Pangean origin and mid‐Cretaceous diversification. Journal of Biogeography 44, p. 2660–2672. · De Miranda G.S., Kulkarni S.S., Tagliatela J., Baker C.M., Giupponi A.P.L., Labarque F.M., Gavish-Regev E., Rix M.G., Carvalho L.S., Fusari L.M., Harvey M.S., Wood H.M. & Sharma P.P., 2024. The Rediscovery of a Relict Unlocks the First Global Phylogeny of Whip Spiders (Amblypygi). Systematic Biology 73, p. 495–505. • 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. · Dunlop J.A. & Lamsdell J.C., 2017. Segmentation and tagmosis in Chelicerata. Arthropod Structure & Development 46, p. 395–418. • Dunlop J.A. & Penney D., 2012. Fossil Arachnids. Monograph Series Vol.2, Siri Scientific Press. 192 pp. • 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.

REFERENCES (part 2) • Garwood R.J. & Dunlop J.A., 2014. Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders. PeerJ 2, e641, 33 pp. • Jocqué R. & Dippenaar-Schoeman A.S., 2007. Spider Families of the World. 2° Edition, Royal Museum of Central Africa, 336 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, · 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. • 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. · Penney D. & Selden P.A., 2012. Fossil Spiders The Evolutionary History of a Mega-diverse Order. Monograph Series Vol.1, Siri Scientific Press. 128 pp. • Sabroux R., 2018. Biodiversité et histoire évolutive des Pycnogonides (Arthropoda, Pycnogonida). Museum national d'histoire naturelle - MNHN PARIS, 345 pp. • Sato S., Derkarabetian S., Valdez-Mondragón A., Pérez-González A., Benavides L.R., Daniels S.R., Giribet G., 2024. Under the hood: Phylogenomics of hooded tick spiders (Arachnida, Ricinulei) uncovers discordance between morphology and molecules. Molecular Phylogenetics and Evolution 193, article 108026. • 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.

To end this thread, I wanted to add a lil' note on humans' perception about chelicerates, and of course some references, I hope this thread helped when it comes to understand what is said in Cheliceratime's posts!^^

Thank you for reading and I’ll see you on the next #Cheliceratime!

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The aquatic chelicerates Chelicerates history began in the sea, and numerous extinct groups show this diversification through the Paleozoic. Most of them are euchelicerates, and this part of the tree is still shaky due to how water to land transition happened more than once. This diversity has become very scarce, only pycnogonids and horseshoe crabs remaining today. The slide showcase a large cladogram of marine chelicerates relationships (basal chelicerates, synziphosurines, chasmataspidids, xiphosurans (horseshoe crabs), eurypterids, and pycnogonids). Pycnogonids are separated from all other groups, while the relationships of euchelicerates are unclear, modern takes suggesting horseshoe crabs, eurypterids & chasmataspids being maybe closer to scorpions & spiders than other arachnids orders.

The arachnopumonates The most stable & monophyletic part of the sub-phylum, made of terrestrial chelicerates breathing ancestrally with book lungs (sometimes modified in tracheae, like with pseudoscorpions & many spiders) and they have a duplicated genome. Arachnopulmonates are mainly divided into panscorpiones (scorpions & pseudoscorpions) & pantetrapulmonates (spiders, vinegaroons, amblypygids, schizomids, haptopods & trigonotarbids)

The apulmonates arachnids Terrestrial chelicerates breathing with tracheae. This part of the chelicerate phylogenetic tree is still unclear and could change drastically in the following years (apart for cephalosomates), ricinuleids being more closely related to arachnopulmonates & fossils lacking to understand these orders’ evolution. They all share non-flagellate spermatozoids. Phalangiotarbids, parasitiform mites & harvestmen are of unknown affinities, solifuges, palpigrades & acariforme mites are grouped together in the cephalosomates, and ricinuleids are closer to horseshoe crabs & arachnopulmonates

The mites Long considered a single group forming the subclass Acari, mites are now strongly separated into 2 unrelated groups, the acariformes and parasitiformes. Their similar morphology and small size appear to be the result of convergent evolution. Arachnologists often consider these 2 groups as orders, but here in Cheliceratime we’ll adopt the ranks acarologists use to reflect how diverse these animals are: 2 super-orders, and at least 6/7 orders (the tree below is super simplified). Even tho some groups are well defined morphologically, numerous large clades are based on genetic & molecular evidence. Acariformes comprise eriophyoids (four-legged mites), various endeostigmates, sarcoptiformes (oridatids & astigmates) and trombidiformes. Parasitiformes are made of opilioacariformes, mesostigmates, holothyrides & ixodides (=ticks)

The many groups of chelicerates have ancient and sometimes still unclear relationships to one another. The 4 slides here summarize where we are on the topic, with some grey areas that could change in the coming years.

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Chelicerates' broad anatomy These animals have complex inner anatomies, with more centralized nervous systems than many arthropods and dorsal hearts. The arrangement of their mouthparts is highly variable depending on the group, from the claws of scorpions to the giant chelicerae of solifuges. Respiration is ensured thanks to gills or skin in water, and book lungs/tracheae/air sacs/skin for land species. Sight is of unequal quality across chelicerates, terrestrial groups having often simple eyes, and sound communication is poorly researched for these arthropods. All chelicerates rely much more on their sense of touch, the numerous setae (=hairs) on their bodies making them super sensitive to their surroundings. This coverage is an essential part of how they perceive the world, and is much more than just hairs like we humans have. It’s the main reason why spiders can look sometimes hairy, but since they don’t have “hair”, let’s say they are fluffy, it’s cute :3

Chelicerates' lifestyles These animals are primarily carnivorous, herbivory being a secondary condition observed mostly among mites. They comprise some of the most important predators in earth’s ecosystems, like the more than 53000 current spider species or the extinct eurypterids that were the apex predators of the Silurian period. Hunting styles are various, with a large amount being sit-and-wait type of hunters, some being scavengers sometimes. Terrestrial groups can’t swallow hard food and need to liquify or squish it before eating. Apart from pycnogonids & several mites, chelicerates larvae often look like tiny adults with softer bodies. Reproduction varies greatly depending on the group considered, even among orders. Life expectancy is widely variable, from a few days for some mites to more than 20 years for certain tarantulas. Many species in temperate regions live 1 year.

"The great arachnid issue" Long thought to be a clean natural group born from a single water to land transition, the traditional view of arachnids has been challenged in the last 15 years. Genomic data suggested new relationships among arachnids, reflecting multiple events of land colonization, with horseshoe crabs right in the middle. At first difficult to believe, this new normal has been globally accepted due to a large amount of unrelated works retrieving the same general trends. In Cheliceratime, the position chosen will be to consider the group called “Arachnida” as similar to Prosomapoda (=crow group euchelicerates) until further research clarifies this part of the tree. It absolutely doesn’t mean that horseshoe crabs evolved from a spider, but that names are just names that can be redefined with new knowledge, and that the arachnid type body plan evolved several times. “Arachnids” as a common name will refer in the posts to the traditional view to encompass easier topics like ecology, general body plan, functional morphology, etc.

An overview of chelicerates' relationships Chelicerates’ phylogeny is... a bit of a mess. Some groups & each order themselves are strongly supported, but it’s still a work in progress with numerous uncertainties concerning terrestrialization events. For the sake of comprehension, they’ll be treated in the further slides in 4 pools, symbolized here by the colors below. AQUATIC CHELICERATES ARACHNOPULMONATES APULMONATE ARACHNIDS MITES The image is an educational infographic: the main content is a stylized phylogenetic tree that runs vertically and branches toward the right. Branch lines are drawn in bright, clean colors — blue, purple, yellow and green — and some branches are dashed or have question marks, signaling uncertainty. Small colored nodes on the left of the tree label higher-level groups (a green dot and a blue dot are visible), and dotted connectors show alternative placements for some groups. Along the right edge of the tree a vertical strip of illustrations shows representative animals aligned with their respective branches: tiny sea spider–like figures near the top, a horseshoe crab & eurypterid-like forms, then scorpion, spider, whip scorpion/amblypygid & vinegaroon, harvestman/daddy-longlegs, camel spider/solifuge, and smaller icons of ticks and mites toward the bottom. The artwork is detailed enough to distinguish those general body plans (long legs, segmented tail and pincers for the scorpion, round body and many legs for mites/ticks).

The biology of chelicerates is an extensive topic covering anatomy, lifecycle, ecology and so on, and recent discoveries have reshaped how we perceived their relationships, tearing up the traditional view of what is an arachnid.

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A diverse group today... Pycnogonids/"Sea spiders" Palpigrades Mites => Acariformes => Parasitiformes Solifugids/"Camel spiders" Harvestmen Ricinuleids Xiphosurans/"Horseshoe crabs" Pseudoscorpions/"False scorpions"/Book scorpions" Scorpions Spiders Uropygids/"vinegaroons"/"whip scorpions" Schizomids Amblypygids/"Whyp spiders"/Tailless whip scorpions"

... as well as a diverse group in the past Mollisonids & Habelids Chasmataspidids 'Synziphosurines' Eurypterids/"Sea scorpions" Phalangiotarbids Trigonotarbids Haptopods Uraraneids & other stem-spiders And other weirdos

Chelicerates' evolutionary history Part 1: 538,8-251,9 million years ago Cambrian (538,8-486,8 Mya) First euchelicerates & pycnogonids appear during the Cambrian explosion as small bottom-dwellers and background species, shadowed by other more ancient groups. Ordovician (486,8-443,1 Mya) Evolutionary radiation, chelicerates become major predators & scavengers in various environments: first eurypterids, chasmataspidids & horseshoe crabs, cryptic terrestrializations, numerous bottom dwellers. Silurian (443,1-419,6 Mya) Eurypterids’ golden age, first members of known firmly terrestrial arachnid lineages (scorpions, trigonotarbids) Devonian (419,6-358,8 Mya) Arachnids radiate on land (first harvestmen, mites & tetrapulmonates) and establish themselves as vital parts of terrestrial ecosystems. Modern pycnogonids appear. Slow decrease in mean size and ecological importance of aquatic euchelicerates (horseshoe crabs, eurypterids, chasmataspidids for the main trio). Carboniferous (358,8-298,9 Mya) Freshwater horseshoe crabs & eurypterids. Confirmed ocurrences of most known arachnids orders with ground-based & arboreal members. Radiation of the tetrapulmonates: first spiders, vinegaroons & amblypygids. Pangea assemblage allows terrestrial & freshwater groups to be distributed worldwide. Permian (298,9-251,9 Mya) Cryptic diversification among mites and other arachnids orders. Permian-Triassic Mass extinction: extinction of many paleozoic groups like eurypterids, trigonotarbids & many primitive lineages, acting as a bottleneck for chelicerates’ diversity.

Chelicerates' evolutionary history Part 2: 251,9 million years ago-Today Triassic (251,9-201,4 Mya) Post extinction recovery & diversification: large cryptic radiation of spiders post Permian-Triassic extinction (potential apparition of the true spider webs), horseshoe crabs radiation in salt & freshwaters. Jurassic (201,4-143,1 Mya) Continuation of Triassic radiations: horseshoe crabs limited to saltwater, spiders already well implemented in ecosystems with various ecological types, modern pycnogonids groups present. Pangea break-up begins to isolate groups in certain continents and leave marks that will guide arachnids’ evolution up to today. Cretaceous (143,1-66 Mya) Huge ecological diversification of spiders linked to the rise of flowering plants & more modern insect fauna: sticking webs become more widespread, development of ground-based species. Intense period of evolutionary radiation on land for groups like schizomids, spiders or amblypygids, facilitated by Pangea break-up and geographic isolation, most of the modern arachnid families (or at least their ancestors) are supposed to appear during this time. Paleogene (66-23 Mya) Araneoids & RTA spiders’ radiation, including the first jumping spiders. Recovery post-extinction, transitional phase between mesozoic and modern faunas. Aquatic chelicerates now restricted to marine horseshoe crabs & pycnogonids. Neogene & Quaternary (23-0 Mya) Modern arachnofauna on land. Scorpion’s venom becomes potent to mammals. Orbweavers, jumping & wolf spiders and several other spider groups become diverse & worldwide.

Chelicerates comprise diverse groups extinct as extant from spiders to mites, eurypterids or other weirdos, and have a rich evolutionary history going back to the cambrian: they've known a time without land plants, the dinosaurs golden age & now they walk alongside us.

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A brief overview Chelicerates are mobile & bilateral animals, part of the arthropods. Like all arthropods, chelicerates have an exoskeleton, grow through molting and have segmented bodies & appendages. If we only look at today’s arthropods, they are the sister group of all the other lineages, meaning they aren’t insects, crustaceans or millipedes, but an entirely separated group. Their origins go way back to the Cambrian explosion, more than 500 million years ago. Chelicerates form a sub-phylum comprising various animals, most of them being carnivorous and walking on 8 or 10 legs: spiders, scorpions, mites, harvestmen, vinegaroons for example, all terrestrial and called “arachnids”, but also the aquatic horseshoe crabs, pycnogonids (=”sea spiders”), the extinct eurypterids & many others.

The chelicera: chelicerates’ most unique feature Chelicerates stand out among arthropods by having no antennae (again, they aren’t insects), instead replaced by their first pair of appendages, called chelicerae (singular chelicera). These are primitively small claws placed before the mouth, and are the prime mouthparts of these animals. They happened to be modified several times across chelicerates’ evolution, being turned into venomous fangs in spiders for example. Scorpions’ large claws are modified manipulatory appendages, their chelicerae are their most upfront little pincers. The slide also display the 3 morphological types of chelicerae: 2 segmented & fangs-like, like in spiders, 2 segmented & claw-like, like in amblypygids, pseudoscorpions & solifuges, and 3 segmented & claw-like, like in horseshoe crabs, pycnogonids, harvestmen or eurypterids

A group of arthropods... Chelicerates share a common ancestor with other arthropods that lived long ago (maybe 540/530 million years ago) and are kinda unique among this giant phylum. According to the most accepted hypothesis (supported for more than 20 years now), a primitive group of arthropods had spines on their first appendages’ pair. Quickly, they shortened, spines grew stronger, segments began to articulate differently and the appendages, now turned into pincer claws, lost their initial sensory function for a mouthpart role: chelicerae were born, and so was the group we call chelicerates. This feature makes chelicerates the only living arthropods without antennae. The slide also features a phylogenetic tree in which chelicerates close to the extinct megacheirians, this clade itself being the sister group to trilobites & mandibulates (millipedes, crustaceans, insects...)

...with specific features Other than chelicerae, chelicerates often exhibit the following features: A body usually subdivided into a functional walking & manipulatory front part, and a raised non-legged posterior part. Front appendages specialized for sensory and feeding purposes. An unmineralized exoskeleton, even among the marine forms. 4 to 5 pairs of walking appendages, sometimes only the last 3 pairs are used to walk. Uniramous appendages, either used to walk & manipulate objects, or for breathing/other life assists.

First, let's begin with a brief introduction and see the main morphological features useful to recognize these animals and where they sit among arthropods.

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What time is it? It’s #Cheliceratime !
No particular species today, we're doing a bit of a recap before going further: in the end, what is a chelicerate?

Answers in the thread below! ⬇️ 🧵

#arthropod #scicom #arachnid #horseshoecrab #pycnogonid #eurypterid #invert #bugsky

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reminder that this funds a raging bigot who is actively contributing to the deaths of trans people, and a cumulatively horrific sociopolitical atmosphere for gender non-conforming people in her home country

and if you aren't from the UK, trust me when I say this is not an exaggeration

This medium-size boxy chasmataspidid was the second species named from this order. It’s known from several specimens, showing a wide range of shapes depending on how they fossilized. Size : 3 to 4-ish cm of body length Time period : Late Cretaceous Paleoart speculativometer : Some Missing parts The animal drawn looks a bit like a boxy shrimp without antennae with an overall brown color

What time is it? It’s #Cheliceratime !
For this entry we're talking about a cute little chasmataspidid, Diploaspis casteri from the Devonian

All the basic infos are here but if you want to learn more, there’s more below!⬇️

#arthropod #devonian #paleoart #sciart #bugsky #invert
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REFERENCES • Dunlop J.A., Poschmann M. & Anderson L.I., 2001. On the Emsian (Early Devonian) arthropods of the Rhenish Slate Mountains: 3. The chasmataspidid Diploaspis. Paläontologische Zeitschrift 75, p. 253–269. · 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. & Briggs D.E.G., 2017. The first diploaspidid (Chelicerata: Chasmataspidida) from North America (Silurian, Bertie Group, New York State) is the oldest species of Diploaspis. Geological Magazine 154, p. 175–180. · Marshall D.J., Lamsdell J.C., Shpinev E. & Braddy S.J., 2014. A diverse chasmataspidid (Arthropoda: Chelicerata) fauna from the Early Devonian ( Lochkovian) of Siberia. Palaeontology 57, 631–655. · 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. · 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. Colorado Plateau Geosystems Inc., 2026. Global Series. In DeepTimeMaps. Online at https://deeptimemaps.com/map-lists-thumbnails/global-series/

And of course: some references, thank you for reading I’ll see you on the next #Cheliceratime!

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