The subcapitulum (from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''sub'', "under", and ''capitulum'', "small head"), also known as infracapitulum, hypognathum or hipognatum, refers to the

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

part of the

gnathosoma The gnathosoma (from Greek , ' = "jaw" and , ' = "body") is the part of the body of the Acari (mites and ticks) comprising the mouth and feeding parts. These are the hypostome, the chelicerae and the pedipalps. It is also called the capitulum (how ...

(the part of the body comprising the mouth and feeding parts) or the fusion of the palpal (of the

pedipalp Pedipalps (commonly shortened to palps or palpi) are the secondary pair of forward appendages among Chelicerata, chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to ...

s, the second pair of

appendages An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

) coxae (the point of union of the appendages with the body) and the labrum (the upper mouthpart) complex present in some

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s on which the mouth, pedipalps, mouthparts and

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

are generally located. It is delimited by the subcapitular

apodeme An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. that of a human) wh ...

(an ingrowth of the

exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

for

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

attachment), which separates it from the cheliceral (of the

chelicerae The chelicerae () are the arthropod mouthparts, mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated ...

, the first pair of appendages) frame.

Acari

The function or

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

of the subcapitulum can vary within

acarine Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as eac ...

s. In its central part, the hypostomal (of the

hypostome In zoology, the hypostome can refer to structures in distinct animal groups: *Hypostome (trilobite), the ventral mouthpart plate in trilobites *Hypostome (tick) The hypostome (also called the maxilla, radula, or Labium (insect), labium) is a Os ...

, a harpoon-like appendage near the mouth) gutter in which the pincers are transformed into a serrated pricking

system A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...

is formed. The anterolateral parts of the subcapitulum might be equipped with cornicula (horn-like processes) or rutella ( hypertrophied

setae In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae ...

on the hypostome). At the base of the hypostome, there can be sternal apophyses, that is, an outgrowth or process in the

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

(lower half of the body segment). In

Mesostigmata Mesostigmata is an order of mites belonging to the Parasitiformes. They are by far the largest group of Parasitiformes, with over 8,000 species in 130 families. Mesostigmata includes parasitic as well as free-living and predatory forms. They ca ...

, this happens in the third segment. The frontal edge of the subcapitulum can be provided with paralaciniae (a pair of small processes). In

Oribatida Oribatida (formerly Cryptostigmata), also known as oribatid mites, moss mites or beetle mites, are an order of mites, in the "chewing Acariformes" clade Sarcoptiformes. They range in size from . There are currently 12,000 species that have been i ...

, its basal section forms a mentum ("chin"). In some acariforms, the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

part forms a "neck". In some cheyletoids and myobiids, the subcapitulum merges with the stylophores (chelicerae formed of fused cheliceral bases) to form a gnathosomal capsule. In some prostigmates, the subcapitulum or the whole capsule is referred to as rostrum.

Other arthropods

The subcapitulum is also present in other

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s. In

Ricinulei Ricinulei is a small order of arachnids. Like most arachnids, they are predatory; eating small arthropods. They occur today in west-central Africa ('' Ricinoides'') and the Americas ('' Cryptocellus'' and '' Pseudocellus'') from Brazil to southern ...

, an

arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

related to acarines, the subcapitulum can also be found. In these organisms, the subcapitulum had a subcapitular apodeme and a crescent-shaped mouth, and lacked

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

lips. In comparison with other arachnids, the ricinuleid subcapitulum may result primitive, but it presents a specialization unique of the order; the coxal regions of the pedipalp are enlarged. Another example would be ''

Necrogammarus ''Necrogammarus salweyi'' is the binomial name applied to an arthropod fossil discovered in Herefordshire, England. The fossil represents a fragmentary section of the underside and an Arthropod leg, appendage of a Pterygotidae, pterygotid eurypt ...

'', an extinct genus of

chelicerate The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks ...

eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...

only known by its subcapitulum and attached pedipalp. In this genus, this structure adopts the form of a discrete plate.

References

Arthropod anatomy Acari {{arthropod-anatomy-stub