The subcapitulum (from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''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 unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

part of the gnathosoma (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 second pair of appendages of chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") a ...

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

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s on which the mouth, pedipalps, mouthparts and

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

are generally located. It is delimited by the subcapitular

apodeme An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the l ...

(an ingrowth of the

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...

for

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

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

chelicerae The chelicerae () are the 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 fangs, or simila ...

, the first pair of appendages) frame.

Acari

The function or morphology of the subcapitulum can vary within acarines. In its central part, the hypostomal (of the hypostome, a harpoon-like appendage near the mouth) gutter in which the pincers are transformed into a serrated pricking system is formed. The anterolateral parts of the subcapitulum might be equipped with cornicula (horn-like

processes A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...

) or rutella ( hypertrophied

setae In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

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 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 blood vessels from injury. ...

(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 c ...

, 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 * Dorsal co ...

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

clades. 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 Neotropics ('' Cryptocellus'' and '' Pseudocellus'') as far north as Texa ...

, an

arachnid Arachnida () is a class of joint-legged invertebrate animals ( arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and ...

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

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 refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...

lips. In comparison with other arachnids, the ricinuleid subcapitulum may result

primitive Primitive may refer to: Mathematics * Primitive element (field theory) * Primitive element (finite field) * Primitive cell (crystallography) * Primitive notion, axiomatic systems * Primitive polynomial (disambiguation), one of two concepts * Pr ...

, 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 appendage of a pterygotid eurypterid, a group of large and pr ...

'', an extinct genus of

chelicerate The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains 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 arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is ...

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