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Chelicerae

Chelicerae are the paired, claw-like appendages that form the anterior-most pair of head structures in arthropods of the subphylum Chelicerata, which encompasses arachnids and several other groups, and they primarily function in feeding by grasping, piercing, or manipulating prey.^[1] These appendages typically consist of two or three segments, with the distal segment often acting against a penultimate one in a pincer-like or fang-like manner, and they are located on the prosoma, the anterior body region fused with the head in arachnids.^[2] While their basic form is conserved across chelicerates, chelicerae exhibit significant variation adapted to diverse lifestyles, such as venom injection in spiders or mechanical shredding in scorpions.^[3] In spiders (order Araneae), chelicerae are specialized as muscular, fang-tipped jaws that move in a scissor-like or vertical fashion to hold prey and deliver venom through a subterminal duct, facilitating immobilization and liquefaction of tissues for consumption, though a few families like Uloboridae lack venom glands.^[4] Scorpions (order Scorpiones) possess smaller, chelate chelicerae resembling pincers, which grasp and tear prey during preoral digestion,^[5] and also play a role in courtship by gripping the female's chelicerae with their own.^[6] Among mites and ticks (subclass Acari), chelicerae often form piercing stylets or barbed structures for cutting into host tissues to extract fluids, while in pseudoscorpions, they include a galea for silk production used in nest-building.^[2]^[5] In other arachnids like solifuges (camel spiders), the chelicerae are massively enlarged and serrated for powerful prey capture and burrowing, highlighting their multifunctional adaptations beyond feeding, including defense and mating.^[1] Beyond arachnids, chelicerae in non-arachnid chelicerates like horseshoe crabs (class Merostomata) are small and pincer-like for mechanical food manipulation without venom, whereas in sea spiders (class Pycnogonida), they are slender probes for piercing soft-bodied prey.^[3] This diversity underscores the chelicerae's evolutionary significance as a defining trait of Chelicerata, enabling a wide array of ecological roles from predation to parasitism across terrestrial, marine, and freshwater habitats.^[1]

Overview

Definition and Characteristics

Chelicerae are paired, claw-like appendages located anterior to the mouth in members of the arthropod subphylum Chelicerata, which includes arachnids, horseshoe crabs, and sea spiders.^[7] The term derives from the Greek words chele (claw) and keras (horn), reflecting their horn-like, grasping structure.^[8] These appendages are a defining synapomorphy of chelicerates, setting them apart from other arthropods by serving as the foremost mouthparts rather than antennae or mandibles.^[9] Key characteristics of chelicerae include their typical segmentation into a basal portion (in spiders, termed the paturon) and a distal movable fang or pincer that articulates via a joint.^[10] This structure enables mobility through associated muscles, allowing for grasping, piercing, or manipulation, though exact forms vary across chelicerate taxa—such as jackknife types in spiders or chelate pincers in scorpions.^[10] In many species, the chelicerae are equipped with fangs connected to glands, enhancing their functional versatility.^[7] Embryologically, chelicerae originate from the deutocerebral segment of the arthropod head, as evidenced by conserved Hox gene expression patterns that confirm the retention of this segment in chelicerates.^[11] This deutocerebral identity is specified by genetic mechanisms, such as the activity of the homothorax gene, which differentiates these appendages from posterior ones across arthropods.^[12] As the primary feeding apparatus, chelicerae underscore the chelicerate body's tagmosis into a prosoma bearing these appendages and the opisthosoma.^[3]

Occurrence in Chelicerates

Chelicerae are the preoral appendages that define the monophyletic subphylum Chelicerata, serving as a key synapomorphy that unites all members of this arthropod lineage.^[13] This subphylum encompasses over 100,000 described extant species, making it the second most diverse arthropod group after Hexapoda.^[13] Chelicerae are universally present across the major chelicerate classes, including the highly diverse Arachnida (spiders, scorpions, mites, ticks, and relatives), the marine Xiphosura (horseshoe crabs), Pycnogonida (sea spiders), and the extinct Eurypterida (sea scorpions).^[13]^[14] These appendages, typically deutocerebral in origin and chelate or pincer-like in form, distinguish Chelicerata phylogenetically from other arthropod subphyla.^[13] The exclusivity of chelicerae to Chelicerata underscores their role as a shared derived trait, absent in the mandibulate arthropods such as Myriapoda (millipedes and centipedes), Crustacea (crabs, shrimp, and lobsters), and Hexapoda (insects and their allies).^[13] In these groups, head appendages evolved convergently toward mandibles for biting and grasping, paired with antennae derived from a different segmental origin, reflecting distinct evolutionary pathways in arthropod head tagmosis.^[13] This morphological divergence supports the deep phylogenetic split between Chelicerata and Mandibulata, with chelicerae emerging as a hallmark of chelicerate monophyly in both molecular and fossil evidence.^[15] Within non-arachnid chelicerates, chelicerae display morphological variation adapted to diverse habitats, though retaining their core pincer-like structure. In Xiphosura, such as the horseshoe crab Limulus polyphemus, chelicerae are reduced in size relative to body proportions, consisting of small, chelate appendages with a pincer at the distal end.^[16] In Pycnogonida, the chelicerae—often termed chelifores—are typically more elongated and clawed, projecting forward from the prosoma to facilitate interaction with marine environments.^[17] These forms highlight the chelicerae's evolutionary plasticity while affirming their presence across Chelicerata's ~120,000 extant species.^[18]

Structure

General Anatomy

Chelicerae are paired, appendage-like mouthparts characteristic of chelicerates, primarily composed of two main segments: a proximal paturon, which serves as the basal portion for articulation and movement, and a distal fang, a sharp, pointed structure adapted for piercing prey or substrates.^[19] The paturon forms the robust base, often housing part of the venom apparatus in certain arachnids, while the fang articulates directly with it via a bicondylar joint, enabling precise extension and retraction.^[20] This two-part configuration allows for efficient prey manipulation and envenomation across diverse chelicerate taxa.^[21] The external structure of chelicerae consists of a cuticular exoskeleton primarily made of chitin reinforced with proteins and sclerotization agents, providing durability and flexibility while minimizing weight.^[22] Sclerotization, a process involving cross-linking of cuticular proteins, hardens the paturon and fang, enhancing resistance to mechanical stress during feeding activities.^[23] Articulations between the paturon and fang, often featuring a fang groove for retraction, permit folding mechanisms that vary by group, such as vertical motion in some basal forms or perpendicular pinching in derived arachnids.^[24] Chelicerae attach anteriorly to the prosoma, the fused head-thorax region in arachnids known as the cephalothorax, positioning them ventral to the mouth for direct access to food sources.^[25] Internal musculature supports their operation, with adductor muscles contracting to close the fang against the paturon and abductor muscles facilitating opening, for enhanced force generation.^[26] These muscles originate within the prosoma and insert via tendons onto the cheliceral segments, enabling rapid strikes.^[27] Variations in cheliceral size and shape reflect ecological adaptations, ranging from minute dimensions in small mites like immature mesostigmatids (body lengths under 0.3 mm) to several centimeters in large scorpions such as Heterometrus species.^[28]^[29] Orientation typically faces medially toward the midline for grasping, though some forms exhibit lateral projections adapted for specific predatory behaviors.^[30]

Segmental Composition

Chelicerae in most arachnids exhibit a two-segmented structure, consisting of a proximal basal segment known as the paturon and a distal movable fang.^[27] This configuration is characteristic of derived arachnid lineages, where the paturon provides structural support and musculature, while the fang enables precise manipulation.^[20] In contrast, more basal chelicerate groups, such as certain extinct eurypterids and chasmataspidids, retain a primitive three-segmented form, with an additional proximal segment articulating basally to the paturon, allowing greater flexibility in early evolutionary contexts.^[31] The segmentation is articulated primarily through hinge joints, which facilitate folding motions essential to cheliceral operation. In jackknife-type chelicerae, a bicondylar hinge connects the paturon and fang, enabling the fang to fold compactly against the paturon when at rest.^[27] Chelates, or pincer-like structures, arise from the opposition of a movable distal finger (the fang) against a fixed proximal finger on the paturon, forming a grasping mechanism without requiring additional segments.^[31] These joint types reflect adaptations derived from the arthropod limb's serial homology, emphasizing mobility over rigidity.^[32] Internally, the fangs of venomous arachnids, such as spiders, are hollow and serve as conduits for venom delivery, connected via a duct that extends from the fang tip to paired venom glands housed within or adjacent to the chelicerae.^[33] These glands, often cylindrical and muscular, allow controlled injection through contraction. Sensory setae, or mechanoreceptive hairs, are distributed across the cheliceral surfaces, providing tactile feedback by detecting mechanical stimuli such as vibrations or contact during manipulation.^[34] Comparatively, chelicerae are homologous to the antennules of crustaceans, representing the deutocerebral appendages in the arthropod ground plan, but have been profoundly modified from primarily sensory functions to manipulative and predatory roles.^[35] Unlike mandibulate arthropods, chelicerates lack true mandibles, necessitating extraoral digestion where enzymes are applied externally to liquefy prey prior to ingestion.^[36]

Functions

Predatory and Feeding Roles

In chelicerates, chelicerae serve as primary appendages for prey capture, enabling the piercing of exoskeletons or skin to immobilize victims through venom injection or mechanical grasping.^[3] In spiders, the chelicerae feature hollow fangs that deliver neurotoxins, such as those targeting ion channels to induce paralysis in insects and other small arthropods.^[37] These fangs penetrate the prey's cuticle, allowing rapid envenomation that subdues larger or more mobile targets efficiently.^[4] For food processing, chelicerae facilitate extraoral digestion, a process characteristic of chelicerates where enzymes are introduced externally to liquefy internal tissues before ingestion. In spiders, the fangs inject digestive fluids alongside venom, breaking down proteins and other macromolecules into a fluid form that is then sucked up through the pharynx.^[36] This method maximizes nutrient extraction while minimizing the ingestion of indigestible solids.^[38] In harvestmen (Opiliones), chelicerae grasp and tear prey into smaller pieces for primarily piecemeal feeding, though extra-oral digestion involving liquefaction also occurs.^[39]^[40] Adaptations in chelicerae enhance their predatory efficiency across taxa; for instance, serrated edges on the cheliceral digits in certain mites, such as Varroa destructor, aid in cutting through host tissues during blood meals.^[41] Chelate forms, common in scorpions, function as pincers to pinch and hold prey securely after immobilization by the tail sting.^[42] These structures often incorporate reinforced cuticles for durability during repeated use.^[43] Representative examples illustrate these roles: scorpions use their chelate chelicerae to crush and shred insects or small vertebrates post-envenomation, after which digestive enzymes are applied to liquefy the remains into ingestible fluids, as they cannot consume solids whole.^[44] In predatory mites like those in the Mesostigmata, chelicerae seize and pierce enchytraeid worms or other microarthropods, with specialized designs optimizing penetration and fluid extraction.^[45]

Sensory and Defensive Functions

Chelicerae in chelicerates often feature chemoreceptors and mechanoreceptors that facilitate the detection of chemical signals from prey or the surrounding environment, as well as tactile sensing for navigating substrates. In ricinuleids, such as Pseudocellus pearsei, the cheliceral digits contain ensheathed gustatory sensilla with terminal pores on the teeth, enabling the perception of chemical cues during prey manipulation, while slit-like mechanoreceptors near the digit articulation detect touch and vibrations for environmental exploration.^[46] Similarly, in spiders like Cupiennius salei, tactile hairs on the chelicerae serve as mechanoreceptors, projecting sensory information centrally to aid in substrate probing and spatial awareness.^[47] In ticks, cheliceral sensilla play a key role in chemosensation beyond initial attachment, housing pore structures that function as chemoreceptors for tasting blood meals and differentiating host suitability prior to feeding. For instance, in Rhipicephalus sanguineus, these inner-digit sensilla allow gustatory assessment, contributing to host location by evaluating chemical profiles encountered during questing behavior.^[48] Tactile setae distributed on chelicerae across arachnids further support mechanosensory functions, such as detecting surface textures during exploration, enhancing overall environmental interaction without reliance on visual cues.^[49] Defensive applications of chelicerae appear in select groups, where they assist in protective behaviors like grooming to dislodge irritants or potential threats. In pseudoscorpions, such as Maxchernes iporangae, the chelicerae are employed to maintain cleanliness by removing debris or parasites from the body, indirectly bolstering defense against infections or environmental hazards while the pedipalps adopt a vigilant posture.^[50] Scorpions similarly utilize their chelicerae for grooming exoskeletal irritants, a function that prevents vulnerability to pathogens and supports overall defensive readiness, though primary protection relies on other appendages.^[51] Specialized sensory roles are evident in pycnogonids, or sea spiders, where chelicerae (chelifores) probe substrates tactilely to locate food sources, integrating mechanoreceptive feedback for precise environmental sampling.^[52] Chelicerae often coordinate with pedipalps during non-feeding tasks, enabling refined manipulation and sensing. In pseudoscorpions, this synergy allows chelicerae to handle silk production or debris while pedipalps provide tactile guidance, as seen in grooming or nest maintenance activities that enhance hygiene and protection.^[53] Such integration underscores the chelicerae's versatility in sensory-defensive contexts, complementing the segmental placement of receptors for efficient appendage interplay.^[54]

Morphological Types

Jackknife Chelicerae

Jackknife chelicerae are a type of two-segmented appendage characterized by a folding mechanism where the basal segment, known as the paturon, articulates with the prosoma and folds upward, while the apical segment, or fang, moves vertically in a downward striking motion reminiscent of a jackknife blade.^[55] This configuration allows for precise penetration and is devoid of chelae, relying solely on the fang for grasping and injection.^[56] These chelicerae predominate in the order Araneae (spiders), where they are the standard form, and occur in other members of the Tetrapulmonata clade, such as Amblypygi (whip spiders) and Uropygi (vinegaroons), but are absent in scorpions (Scorpiones), which possess three-segmented chelate chelicerae.^[56] In Opiliones (harvestmen), chelicerae are typically three-segmented and non-jackknife, though some species exhibit elongated forms adapted for specific behaviors.^[57] Functionally, the jackknife design facilitates envenomation from an overhead position, enabling spiders to subdue prey larger than themselves by injecting venom through the hollow fang.^[55] In spiders, the fang connects directly to expansive venom glands housed in the prosoma, which produce potent cocktails of neurotoxins and enzymes tailored for immobilizing and liquefying diverse prey.^[55] Variations in jackknife chelicerae include differences in paturon size and orientation; for instance, in araneomorph spiders like jumping spiders (Salticidae), the paturon is often elongated and robust, enhancing precision in prey capture and mate interactions.^[58] Orthognathous forms, seen in mygalomorph spiders, feature parallel-facing chelicerae, while labidognathous types in araneomorphs converge medially for more versatile striking.^[55]

Uncate Chelicerae

Uncate chelicerae represent a morphological variant characterized by a two-segmented structure consisting of a fixed paturon and a curved, hook-like fang, derived from the Latin "uncus" meaning hook. Unlike folding types, these chelicerae lack a hinge for vertical closure and instead operate through horizontal or lateral movements facilitated by a bicondylar joint, enabling scissor-like action for prey manipulation. The fang is typically sickle-shaped, with dentition on both fixed and movable segments, including primary teeth and secondary denticles that enhance cutting efficiency.^[59]^[60] This type is distributed among certain arachnid orders, notably select families of Solifugae (camel spiders), such as Solpugidae and Eremobatidae, which exhibit robust, chelate forms. They also appear in basal arachnids, including some pseudoscorpions and ricinuleids, reflecting an ancestral configuration in chelicerate evolution. In Solifugae, they can exceed prosoma length, underscoring size-related adaptations.^[60]^[59]^[61] Functionally, uncate chelicerae excel in slashing and tearing soft-bodied prey, such as insects and small arthropods, through mechanical shear rather than venom injection, as these structures lack associated venom glands. Solifugae employ a similar "cheliceral mill" mechanism, where overlapping teeth grind tissues, with females showing more robust forms for predation and males featuring slender, hooked modifications for mating behaviors like spermatophore transfer. This emphasis on physical damage suits nocturnal, opportunistic foraging in leaf litter or soil habitats.^[60]^[59] Variations in uncate chelicerae primarily involve fang curvature, tailored to prey size and habitat; for instance, broader curves in Solifugae like Eremobates facilitate larger vertebrate carrion. Sexual dimorphism is pronounced in Solifugae, with male flagella—modified setae on the fixed finger—ranging from setiform to composite structures aiding copulation. These adaptations highlight the versatility of uncate forms without compromising their core slashing role.^[60]^[59]

Three-Segmented Chelate Chelicerae

Three-segmented chelate chelicerae consist of a proximal basal segment, a medial segment bearing a fixed finger, and a distal movable finger that opposes the fixed one to form a pincer-like chela capable of clamping and grasping.^[31]^[62] This structure allows for precise manipulation, with the opposed digits enabling the chelicerae to hold objects securely through a shearing or pinching motion.^[63] This cheliceral type is distributed among several arachnid orders, including Scorpiones (scorpions), Opiliones (harvestmen), and certain subgroups of Acari (mites), as well as in extinct eurypterids (sea scorpions).^[31]^[7]^[57] In scorpions, the chelicerae are positioned anteriorly on the prosoma and articulate with the body via a basal joint.^[64] Within Acari, chelate forms predominate in mesostigmatid mites, where the three segments support diverse feeding adaptations, and in Opiliones, the chelicerae consist of three segments with the distal two forming a toothed pincer.^[45]^[57] Functionally, these chelicerae serve primarily in predatory and feeding roles by grasping small prey or food particles, facilitating their transport to the mouthparts.^[31] In scorpions, following envenomation by the telson, the chelicerae manipulate and tear the immobilized prey, aiding in dissection and ingestion while also assisting in grooming.^[64] In Opiliones, the chelicerae grasp and tear prey without venom. In mites, the chelae grasp minute prey or pierce host tissues to extract fluids, with the pincer action porting material toward the pharynx for sucking.^[45] Variations in this cheliceral form include significant size differences, ranging from microscopic pincers in mites (under 0.1 mm) to robust, macro-scale structures in scorpions (up to several centimeters).^[45]^[64] Sexual dimorphism occurs in some scorpion species, where males possess enlarged chelicerae relative to females, potentially enhancing their role in mate grasping during courtship.^[65] Such dimorphism underscores adaptive modifications for reproductive behaviors without altering the fundamental three-segmented chelate design.^[66]

Evolution

Origins in Arthropods

The origins of chelicerae trace back to the early evolutionary history of arthropods, with the fossil record providing key insights into their emergence. Chelicerae-like structures, interpreted as grasping appendages homologous to modern chelicerae, first appear in middle Cambrian trilobitomorph arthropods from deposits such as the Burgess Shale, dating to approximately 508 million years ago. These structures, seen in taxa like Sanctacaris uncata, suggest an early specialization of frontal appendages for manipulation, though their exact chelicerate affinity remains debated. Definitive chelicerae, more clearly resembling those of extant chelicerates, are documented in Ordovician synziphosurines, such as Setapedites abundantis from deposits around 478 million years ago, marking a consolidation of the chelicera as a diagnostic feature of the group.^[67]^[68] Developmentally, chelicerae arise from the deutocerebral segment of the arthropod head during embryogenesis, originating as limb buds innervated by the deutocerebrum. This positioning reflects a conserved pattern across arthropods, where the deutocerebral appendages differentiate from more posterior locomotory limbs through genetic mechanisms involving Hox gene regulation and distal-less expression. In chelicerates, this co-option transformed ancestral walking appendages into specialized feeding tools, enabling precise grasping and piercing, as evidenced by comparative studies of embryonic development in spiders and horseshoe crabs. Such modifications highlight how segmental identity shifts underpinned the functional evolution of chelicerae from generalist to specialized roles.^[12]^[69]^[56] Evolutionary hypotheses propose that chelicerae derived from biramous appendages typical of basal arthropods, through the reduction or loss of the exopod (outer branch) and associated flagella, resulting in a compact, uniramous form suited for predation. This transformation is linked to ecological shifts in marine ancestors, where early arthropods transitioned from passive filter-feeding—relying on biramous limbs for suspension capture—to active predation, with chelicerae providing a mechanical advantage for seizing prey. Fossil evidence from Cambrian great-appendage arthropods, such as Haikoucaris, supports this, showing intermediate forms with short, spiny frontal appendages akin to proto-chelicerae.^[56]^[70]^[13] A pivotal event in chelicerae evolution was their establishment in stem-group chelicerates during the Great Ordovician Biodiversification Event (GOBE), spanning roughly 485 to 443 million years ago, when marine ecosystems underwent rapid faunal expansion. This period saw the proliferation of synziphosurine-like stem chelicerates, such as Setapedites abundantis, featuring chelicerae adapted to diverse benthic habitats, coinciding with increased oxygen levels and plankton blooms that favored predatory innovations. The GOBE thus provided the environmental context for chelicerae to become entrenched as a hallmark of chelicerate radiation, setting the stage for subsequent diversification.^[71]^[68]

Diversification Across Groups

The diversification of chelicerae within arachnids accelerated after the Silurian period, approximately 420 million years ago, aligning with the transition to terrestrial habitats and the radiation of major lineages such as spiders and scorpions.^[72] In spiders (Araneae), the two-segmented jackknife form emerged as a derived adaptation for efficient prey manipulation on land, facilitated by the loss of the proximal segment through genetic mechanisms involving the dachshund domain.^[56] Similarly, scorpions (Scorpiones) retained three-segmented chelate chelicerae suited to burrowing and soil-based predation, reflecting their early divergence and adaptation to terrestrial microhabitats.^[56] Outside arachnids, non-arachnid chelicerates exhibit retention or modification of ancestral forms. Horseshoe crabs (Xiphosura) preserve the primitive three-segmented chelicerae, consisting of a proximal paturon and distal claw-like segments, which serve basic feeding functions in marine environments and highlight the plesiomorphic condition across Chelicerata.^[31] In sea spiders (Pycnogonida), chelicerae manifest as elongated chelifores, particularly in deep-sea species like Colossendeis colossea, enabling probing and capture in low-visibility aquatic habitats.^[73] Key drivers of this diversification include habitat adaptations and co-evolutionary innovations. Terrestrialization prompted morphological shifts, such as the evolution of venom delivery systems in spider chelicerae around 300 million years ago, originating from ancestral gene duplications in early araneomorphs to enhance predation efficiency.^[74] In web-building spiders, the development of silk glands paralleled cheliceral evolution, potentially reducing reliance on chelicerae for direct prey handling by enabling passive capture strategies.^[75] In modern lineages, cheliceral diversification includes reductions or losses, particularly in parasitic forms. Parasitic mites, such as those in the genus Demodex, display extreme reduction of chelicerae into piercing stylets for host tissue penetration, an adaptation tied to their endoparasitic lifestyle within mammalian follicles.^[76] This spectrum of forms underscores ongoing evolutionary plasticity, with fossil records suggesting untapped potential for discovering intermediate morphologies in undescribed deposits.^[32]

References

[1]
Arachids - Susan Masta - Portland State University
Arachnids are widespread, diverse chelicerates, a major group of arthropods, with 4 pairs of legs, 1 pair of pedipalps, and 1 pair of chelicerae.
[2]
None
### Summary of Chelicerae in Arachnids
[3]
Section 2: Body Plan - EdTech Books
The chelicerae are the defining appendages of Chelicerata, adapted for feeding, defense, and manipulation of prey. These first pair of appendages vary ...
[4]
Spider Anatomy - Pedipalps - University of Kentucky
Nov 19, 2009 · Chelicerae are filled with muscles, and are used to hold prey while the spider injects venom. Note that a few rare spiders, such as those in the ...
[5]
[PDF] Amazing Arachnids - chapter 1 - Princeton University
Arachnids have two chelicerae, eight legs, eight eyes, and a hardened exoskeleton. They are arthropods with segmented bodies and jointed appendages.
[6]
Chelicerata - Digital Atlas of Ancient Life
Chelicerae, meaning “claw horn” in Greek, are a pair of appendages anterior to (i.e., in front of) the mouth.
[7]
Chelicera - Definition and Examples - Biology Online Dictionary
Sep 23, 2021 · The first pair of these appendages is termed chelicerae, which etymologically means jaws or horns and from where the name of this group is ...
[8]
Phylum Arthropoda | manoa.hawaii.edu/ExploringOurFluidEarth
They instead possess a set of clawed appendages called chelicerae that are used to grab and shred food. Most chelicerates are terrestrial; exceptions are the ...
[9]
Morphology and performance of the 'trap-jaw' cheliceral strikes in ...
Spider chelicerae are composed of two different sections, a basal section (the paturon) that articulates with the carapace, and a distal section composed of ...<|control11|><|separator|>
[10]
[PDF] ARACHNIDS - Smithsonian Institution
chelicerae (chelate) The first pair of preoral append- ages. They are at most three segmented, usually two, and usually the distal segment acts against the ...
[11]
A conserved mode of head segmentation in arthropods revealed by ...
Chelicerates constitute a basic arthropod group with fossil representatives from as early as the Cambrian period. Embryonic development and the subdivision ...
[12]
A conserved genetic mechanism specifies deutocerebral ... - Journals
Jun 7, 2015 · The deutocerebral (second) segment of the head is putatively homologous across Arthropoda, as inferred from the segmental distribution of the ...
[13]
The Phylogeny and Evolutionary History of Arthropods - ScienceDirect
Jun 17, 2019 · Chelicerates include numerous extinct and extant lineages of arthropods and are characterized by a pair of deutocerebral appendages (innervated ...
[14]
[PDF] Geological history and phylogeny of Chelicerata
Chelicerata probably appeared during the Cambrian period. Their precise origins remain unclear, but may lie among the so-called great appendage arthropods.
[15]
Increasing species sampling in chelicerate genomic-scale datasets ...
May 24, 2019 · Chelicerata is the second largest subphylum of arthropods, outnumbered only by insects. ... The evolutionary history of the chelicerates extends ...
[16]
Limulus polyphemus - Lander University
The anteriormost appendages are the characteristic chelicerae of chelicerate arthropods. The chelicerae are relatively small and end with a pincer, or chela.
[17]
The chelifores of sea spiders (Arthropoda, Pycnogonida) are the ...
Oct 27, 2008 · By providing direct morphological support for the deutocerebral status of the cheliforal ganglia, we reconcile morphological and gene expression ...
[18]
Chelicerates - ScienceDirect.com
Jul 23, 2018 · Two groups of chelicerates are marine, the horseshoe crabs (Xiphosura) and the sea spiders (Pycnogonida), which together constitute less than 2% ...
[19]
https://www.sciencedirect.com/science/article/pii/B9780128096338022433
[20]
web builders have lower estimated biting forces than free hunters
Nov 26, 2024 · Spider chelicerae comprise two segments, a distal fang and a proximal paturon (cheliceral base), connected at a strong bicondylar articulation.
[21]
https://www.sciencedirect.com/science/article/pii/B978012374144800014X
[22]
The spider cuticle: a remarkable material toolbox for functional ...
The exoskeleton of spiders is made of a few main building blocks only: chitin and proteins, sclerotization agents and water. These are organized ...
[23]
Arthropod Exoskeleton - an overview | ScienceDirect Topics
Arthropods have an exoskeleton made of chitin. 1 The main functions of a chitinous exoskeleton are to provide support and impede fluid loss.Entomogenous Fungi · Fungus--Host Interactions... · Cartilage Tissue EngineeringMissing: chelicerae | Show results with:chelicerae
[24]
https://www.sciencedirect.com/science/article/pii/B9780125104517500256
[25]
https://www.sciencedirect.com/science/article/pii/B978012814043700025X
[26]
The role of hydraulic pressure in spider cheliceral function
Current hypotheses for the function of individual muscles are derived largely from names (adductor, abductor, levator, depressor, etc.) inferred from ...
[27]
Dichotomous Key for Microarthropod Identification - Mites And Other ...
Fig. 32. Dark chelicerae ; 40a, Immature mesostigmatid that is 300 μm or smaller in length, Small Pale Mesostigmatids ; 40b, Immatue mesostigmatid larger than 300 ...
[28]
Scorpion - Types, Size, Diet, Anatomy, Habitat, Life Cycle & Pictures
Sep 3, 2025 · Size. On average, scorpions are typically around 6 cm (2.5 inches) long ... The chelicerae are the pincer-like mouthparts of the scorpion ...
[29]
Morphological Analysis Reveals a Compartmentalized Duct in the ...
Apr 9, 2021 · The orientation of the chelicerae is labidognathous, which means they are directed towards each other. Some sensory hairs are present on the ...
[30]
[PDF] "Chelicerata (Arachnids, Including Spiders, Mites and Scorpions)". In
The first pair of prosomal appendages is the chelicerae, which serve as the primary feeding organs. In their primitive form, the chelicerae are composed of ...<|separator|>
[31]
The “elongate chelicera problem”: A virtual approach in an extinct ...
May 17, 2024 · Chelicerae, distinctive feeding appendages in chelicerates, such as spiders, scorpions, or horseshoe crabs, can be classified based on their ...
[32]
Venom gland organogenesis in the common house spider - Nature
Jul 4, 2024 · The venom apparatus consists of a pair of secretory glands, each connected to an opening at the fang tip by a duct that runs through the ...
[33]
The spider cuticle: a remarkable material toolbox for functional ...
Aug 2, 2021 · Most of those setae are innervated and have a sensory function. Deflection of the hair shaft elicits a neuronal response. The hair is suspended ...<|separator|>
[34]
Development of the nervous system in the "head" of Limulus ...
Nov 30, 2002 · The neuromere of the chelicerae is homologous to the deutocerebrum of crustaceans and hexapods connected to the antennae. Regarding the ...Limulus Polyphemus · Mandibulates · Discussion<|separator|>
[35]
Characterisation of protein families in spider digestive fluids ... - NIH
Aug 10, 2017 · Many spiders mechanically break a hole into the cuticle of an insect by the use of their chelicerae and subsequently inject venom and digestive ...
[36]
Spider Venom: Components, Modes of Action, and Novel Strategies ...
Most spider venom toxins can be either classified as “classic” AMP or “classic” neurotoxin-like peptide. Some toxins, however comprise a multi-domain ...
[37]
Digestive enzymes and sphingomyelinase D in spiders without ... - NIH
Feb 15, 2023 · Spiders digest a large amount of food by regurgitating the digestive fluid from their midgut in a process known as extra-oral digestion (EOD).
[38]
Ohio's Natural Enemies: Harvestmen (also known as daddy longlegs)
Jan 14, 2016 · Unlike spiders who inject venom into their prey, harvestmen simply grasp it with their chelicerae and pedipalps and tear it apart to consume it.
[39]
[PDF] Insights Into the Feeding Behaviors and Biomechanics of <i>Varroa ...
Sep 25, 2019 · using paired, movable toothed digits of chelicerae, together with paired elongated corniculi having sharpened, serrated ventral edges, suitable.
[40]
Armed stem to stinger: a review of the ecological roles of scorpion ...
The first pair is used for feeding and forms the mouth parts or chelicerae. The second pair forms the pedipalps ending in the pincers or chelae. The other ...
[41]
Material composition and mechanical properties of the venom ...
Aug 23, 2024 · Many arthropods incorporate reinforcing elements into the cuticle of their piercing or biting structures to enhance hardness, elasticity or ...
[42]
[PDF] Scorpions - Utah State University Extension
Scorpions cannot ingest solid food. Once the prey has been paralyzed, the scorpion will pinch off sections using their chelicerae.
[43]
Feeding design in free-living mesostigmatid chelicerae (Acari
This review shows that predatory mesostigmatids do have cheliceral designs with clear rational purposes.
[44]
(PDF) Taste while chewing? Sensory structures in the chelicerae of ...
Aug 9, 2025 · PDF | Sensory structures in the chelicerae of Pseudocellus pearsei (Chamberlin & Ivie, 1938) (Ricinulei, Arachnida) were studie under light ...Missing: capabilities | Show results with:capabilities
[45]
Central projections of cheliceral mechanoreceptors in the spider ...
Central projections of lyriform organs and tactile hairs on the chelicerae of the wandering spider Cupiennius salei were traced using anterograde cobalt ...<|separator|>
[46]
Study on cheliceral sensilla of the brown dog tick Rhipicephalus ...
They house two pore sensilla in the inner digit that act as chemoreceptors. Ticks can taste their blood meal through these appendages, given that neurons in the ...
[47]
Distribution and development of the external sense organ pattern on ...
Feb 8, 2020 · Here we analyse the development of the pattern and distribution of six different external mechano- and chemosensory organs in all postembryonic ...Missing: capabilities | Show results with:capabilities
[48]
Feeding in Maxchernes iporangae (Pseudoscorpiones, Chernetidae ...
During feeding, the prey was held only by the chelicerae, and the palps were kept free and direct? ed laterally, in a characteristic defensive posture, as.
[49]
[PDF] Scorpions - The University of Arizona
As arachnids, scorpions have mouthparts called chelicerae, a pair of pedipalps, and four pairs of legs. The pincer-like pedipalps are used primarily for prey ...
[50]
The chelifores of sea spiders (Arthropoda, Pycnogonida) are the ...
Aug 9, 2025 · Examination of the sensory organs revealed unusually organized eyes, mechanoreceptors, and chemoreceptors. We have uncovered a mixed sensory ...
[51]
Anatomy of the Nervous System in Chelifer cancroides (Arachnida
Neurons associated with the pedipalps terminate in two regions in the central nervous system of characteristic arrangement: a glomerular and a layered center.<|control11|><|separator|>
[52]
[PDF] Evolution and development of sensory systems in Chelicerata By ...
sensory function. The primordium of the stomodeum begins to form medially on the head lobes. (Fig. 6F). The germband is narrower than in the previous stage ...
[53]
The biology and evolution of spider venoms - Wiley Online Library
Aug 28, 2021 · In spiders, the chelicerae feature two functional units that move in a jack-knife fashion. The first unit, a basal segment, is attached to ...
[54]
[PDF] Evolution of the chelicera: a dachshund domain is ... - Extavour Lab
Expression of homeobox genes shows chelicerate arthropods retain their deutocerebral seg- ment. Proc. Natl. Acad. Sci. USA 95: 10671–10675. Thomas, R. H. ...
[55]
Kinematics of elongate harvestmen chelicerae: Comparative range ...
While the bipartite chelicerae resembling a "jackknife" configuration in spiders appear to represent a derived character state, the presence of three-segmented ...
[56]
Descriptions of three new species of jumping-spiders, genus ...
Feb 24, 2020 · Chelicerae with orange-brown paturon, bearing extremely elongated spear-like apophyses on their ectal side (Fig. 4A, B, 5A, B, 7A). Abdomen oval ...<|control11|><|separator|>
[57]
[PDF] DISSERTATION CHELICERAL MORPHOLOGY OF SOLIFUGAE ...
The chelicerae provide the most important character systems for solifuge systematics, including dentition and the male flagellum, both used extensively in ...
[58]
https://zse.pensoft.net/article/46509/
[59]
Genomic resources and toolkits for developmental study of whip ...
Whip spiders are emerging as model systems in behavioral ecology, learning, and neurophysiology in arachnids [50, 51]. Their pedipalps, the second pair of ...Missing: feeding | Show results with:feeding
[60]
Chelicerae - an overview | ScienceDirect Topics
If the basal segment has a finger-shaped outgrowth against which the distal segment operates, the chelicerae are chelate (as in scorpions or harvestmen). If not ...
[61]
All mites have a small head - Lucid key
The maximum number of cheliceral segments in mites is three: a basal article, a middle article that usually ends in a fixed digit, and a movable digit that ...<|control11|><|separator|>
[62]
General - Scorpions - Panarthropoda.de
The foremost extremeties of the prosoma are the chelicerae, three segmented and scissor-like feeding appendages, that are also used for grooming and cleaning ...
[63]
Chelicerae as male grasping organs in scorpions: sexual ... - PubMed
In the present study, we determine whether there is a relationship between a novel record of scorpion sexual dimorphism, the sexual dimorphism of chelicerae ...
[64]
Chelicerae as male grasping organs in scorpions - ResearchGate
Aug 6, 2025 · In the present study, we determine whether there is a relationship between a novel record of scorpion sexual dimorphism, the sexual dimorphism ...
[65]
[PDF] a middle cambrian chelicerate from - The Palaeontological Association
The biramous appendages (and lack of chelicerae, if real) define the position of. Sanctacaris as a primitive sister group of all other chelicerates and we ...
[66]
Lower Ordovician synziphosurine reveals early euchelicerate ...
May 7, 2024 · Euchelicerates have traditionally been united by the presence of specialized frontal-most appendages, the so-called chelicerae, and by the ...
[67]
Expression of homeobox genes shows chelicerate arthropods retain ...
The chelicerate deutocerebral segment has not been reduced or lost. We make further inferences concerning the evolution of heads and Hox genes in arthropods.Missing: origin | Show results with:origin
[68]
A new 'great‐appendage' arthropod from the Lower Cambrian of ...
Expression of homeobox genes shows chelicerate arthropods retain their deutocerebral segment 1998; 95, Proceedings of the National Academy of Sciences, 10671– ...
[69]
A Hypothesis on Suspension Feeding in Early Chelicerates ...
The Cambrian–Ordovician Plankton Revolution played a crucial role in the Great Ordovician Biodiversification Event (GOBE) or Ordovician Radiation, ...
[70]
Consensus and conflict in studies of chelicerate fossils and phylogeny
Dec 29, 2023 · Biramous limbs are widely accepted by palaeontologists as having characterised the last common ancestor of all arthropods; for recent summaries ...Tab. 1 · Fig. 3 · Fig. 4
[71]
https://www.mdpi.com/1424-2818/17/6/412
[72]
Comparative venomics suggests an evolutionary adaption of spider ...
Oct 23, 2025 · A Habitus and defensive behavior of C. punctorium, displayed by an adult female presenting its opened chelicerae towards a potential threat as ...
[73]
Genomic and transcriptomic analyses support a silk gland origin of ...
Apr 13, 2023 · Previous studies have hypothesized that spider venom glands originated from salivary glands or evolved from silk-producing glands present in early chelicerates.<|separator|>
[74]
Human Follicular Mites: Ectoparasites Becoming Symbionts
Jun 21, 2022 · Follicular mites show an extreme reduction of the chelicerae in combination with more developed (protruding) pedipalps, especially in nymphal ...