Mouthparts
Encyclopedia
The mouthparts of arthropod
s have evolved
into a number of forms, each adapted
to a different style or mode of feeding. Most mouthparts represent modified, paired appendage
s, which in ancestral forms would have appeared more like legs than mouthparts. In general, arthropods have mouthparts for cutting and chewing, piercing and sucking, siphoning, and filtering. This article outlines the basic elements of four arthropod groups: insects, myriapods, crustaceans and chelicerates. Insects are used as the model, with the novel mouthparts of the other groups introduced in turn. Insects are not, however, the ancestral form of the other arthropods discussed here.
mouthparts exhibit a range of forms. The earliest insects had chewing mouthparts. Specialisation includes mouthparts modified for siphoning, piercing, sucking and sponging. These modifications have evolved a number of times. For example, mosquitoes (which are flies) and aphids (which are bugs) both pierce and suck; however, female mosquitoes feed on animal blood whereas aphids feed on plant fluids. This section provides an overview of the individual mouthparts of chewing insects.
Myriapods comprise four classes
of arthropod, each with a similar morphology
: Class Chilopoda (centipedes); class Diplopoda (millipedes); class Pauropoda
; and class Symphyla
.
Myriapod mouthparts
are similar to those of chewing insects, although there is some variation between the myriapod classes. A labrum is present but sometimes is not obvious and forms an upper lip, often in association with an epistome. The labium is formed by first maxillae in diplopoda forming the gnathochilarium. The preoral cavity so-formed contains paired mandibles and any maxillae which are present.
s, in addition to their mouthparts, possess a pair of "poison claws", or forcipules. These, like the maxillipeds of crustaceans, are modified legs and not true mouthparts. The forcipules arise from the first body segment, curving forward and to the midline. The tip is a pointed fang, which has an opening from a venom gland. The forcipules are used to capture and poison prey.
s comprise a number of classes, with various feeding modes supported by a range of adaptions to the mouthparts. In general, however, crustaceans possess paired mandibles with opposing biting and grinding surfaces. The mandibles are followed by paired first and second maxillae. Both the mandibles and the maxillae have been variously modified in different crustacean groups for filter feeding with the use of setae.
es of arthropod, with similar gross morphology but defining differences: Class Xiphosura
(horseshoe crabs); class Eurypterida (the extinct eurypterids); class Arachnida (spider
s, scorpion
s, tick
s and mite
s); and class Pycnogonida (sea spiders).
Chelicerates are in part defined by possessing chelicerate appendages, although crustaceans also possess chelate appendages. Chelicerates are more easily distinguished from other arthropods in lacking antennae
.
are chelate appendages that are used to grasp food. For example, in horseshoe crabs, they are like pincers, whereas in spiders, they are hollow and contain (or are connected to) venom glands and are used to inject venom to disable prey prior to feeding. In some spiders, the chelicerae have teeth, which are used to macerate prey items to assist digestion by secreted enzymes. Those spiders without toothed chelicerae inject digestive enzymes directly into their prey. Mites and ticks have a range of chelicerae. Carnivores have chelicerae that tear and crush prey, whereas herbivores can have chelicerae that are modified for piercing and sucking (as do parasitic species). In sea spiders, the chelicerae (also known as chelifores) are short and chelate and are positioned on either side of the base of the proboscis or sometimes vestigial or absent.
s. In scorpions, the pedipalps are large and chelate (of the scissor type at Figure 4). They are used to capture and hold prey items for stinging before the chelicerae tear the prey into items for digestion. In spiders, the pedipalps of males are modified and function as secondary sex organs (transmission of sperm to the female). The pedipalps of mites and ticks vary depending on the species' feeding mode. They are segmented and may be leg-like or chelate, like a second pair of chelicerae.
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s have evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
into a number of forms, each adapted
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
to a different style or mode of feeding. Most mouthparts represent modified, paired appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
s, which in ancestral forms would have appeared more like legs than mouthparts. In general, arthropods have mouthparts for cutting and chewing, piercing and sucking, siphoning, and filtering. This article outlines the basic elements of four arthropod groups: insects, myriapods, crustaceans and chelicerates. Insects are used as the model, with the novel mouthparts of the other groups introduced in turn. Insects are not, however, the ancestral form of the other arthropods discussed here.
Insects
InsectInsect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
mouthparts exhibit a range of forms. The earliest insects had chewing mouthparts. Specialisation includes mouthparts modified for siphoning, piercing, sucking and sponging. These modifications have evolved a number of times. For example, mosquitoes (which are flies) and aphids (which are bugs) both pierce and suck; however, female mosquitoes feed on animal blood whereas aphids feed on plant fluids. This section provides an overview of the individual mouthparts of chewing insects.
Labrum
The labrum is a flat extension of the head (below the clypeus), covering the mandibles. Unlike other mouthparts, the labrum is a single, fused plate (though it originally was—and embryonically is—two structures). It is the upper-most of the mouthparts and located on the midline. It serves to hold food in place during chewing by the mandibles and thus can simply be described as an upper lip.Mandible
Chewing insects have two mandibles, one on each side of the head. They are typically the largest mouthpart of chewing insects, being used to masticate (cut, tear, crush, chew) food items. They open outwards (to the sides of the head) and come together medially.Maxilla
Paired maxillae cut food and manipulate it during mastication. Maxillae can have hairs and "teeth" along their inner margins. At the outer margin, the galea is a cupped or scoop-like structure, which sits over the outer edge of the labium. They also have palps, which are used to sense the characteristics of potential foods.Labium
The labium is a single structure, although it is formed from two fused secondary maxillae. It can be described as the floor of the mouth. With the maxillae, it assists manipulation of food during mastication.Hypopharynx
The hypopharynx is a somewhat globular structure, arising from the base of the labium. It assists swallowing.Myriapods
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
of arthropod, each with a similar morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
: Class Chilopoda (centipedes); class Diplopoda (millipedes); class Pauropoda
Pauropoda
Pauropods are small, pale, centipede-like arthropods. They form the order Pauropodina, belonging to the monotypic class Pauropoda. About 500 species in four families are found worldwide, living in soil and leaf mold...
; and class Symphyla
Symphyla
Symphylans, also known as garden centipedes or glasshouse symphylans, are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda. Symphylans resemble centipedes, but are smaller and translucent. They can move rapidly through the pores between soil particles, and are typically...
.
Myriapod mouthparts
Mouthparts
The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired appendages, which in ancestral forms would have appeared more like legs than mouthparts. In general, arthropods have mouthparts for...
are similar to those of chewing insects, although there is some variation between the myriapod classes. A labrum is present but sometimes is not obvious and forms an upper lip, often in association with an epistome. The labium is formed by first maxillae in diplopoda forming the gnathochilarium. The preoral cavity so-formed contains paired mandibles and any maxillae which are present.
Forcipules
CentipedeCentipede
Centipedes are arthropods belonging to the class Chilopoda of the subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. Centipedes have an odd number of pairs of...
s, in addition to their mouthparts, possess a pair of "poison claws", or forcipules. These, like the maxillipeds of crustaceans, are modified legs and not true mouthparts. The forcipules arise from the first body segment, curving forward and to the midline. The tip is a pointed fang, which has an opening from a venom gland. The forcipules are used to capture and poison prey.
Crustaceans
CrustaceanCrustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s comprise a number of classes, with various feeding modes supported by a range of adaptions to the mouthparts. In general, however, crustaceans possess paired mandibles with opposing biting and grinding surfaces. The mandibles are followed by paired first and second maxillae. Both the mandibles and the maxillae have been variously modified in different crustacean groups for filter feeding with the use of setae.
Maxillipeds
Up to the first three pairs of legs are modified to maxillipeds, which assist manipulation of food items by passing food forward to the mandibles for chewing or to the maxillae for cutting into smaller pieces.Setae
Filter feeding crustaceans have setae on modified appendages that act as filters. Filter feeding may have developed in association with swimming, with early morphological adaptions occurring on the appendages of the body trunk. Subsequent adaptions appear to have favoured forward filtering appendages. Filtering appendages generate water currents that bring food items into reach for collection by setae. Other setae may be used to brush the filtering setae clean, and yet other setae may transport food items to the mouth.Cirri
Barnacles have thoracic appendages modified for feeding, the cirri, which filter suspended food particles from water currents and pass the food to the mouth.Chelicerates
Chelicerates comprise four classClass (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
es of arthropod, with similar gross morphology but defining differences: Class Xiphosura
Xiphosura
Xiphosura is an order of marine chelicerates which includes a large number of extinct lineages and only four recent species in the family Limulidae, which include the horseshoe crabs...
(horseshoe crabs); class Eurypterida (the extinct eurypterids); class Arachnida (spider
Spider
Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s, scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
s, tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
s and mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s); and class Pycnogonida (sea spiders).
Chelicerates are in part defined by possessing chelicerate appendages, although crustaceans also possess chelate appendages. Chelicerates are more easily distinguished from other arthropods in lacking antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
.
Chelicerae
CheliceraeChelicerae
The chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...
are chelate appendages that are used to grasp food. For example, in horseshoe crabs, they are like pincers, whereas in spiders, they are hollow and contain (or are connected to) venom glands and are used to inject venom to disable prey prior to feeding. In some spiders, the chelicerae have teeth, which are used to macerate prey items to assist digestion by secreted enzymes. Those spiders without toothed chelicerae inject digestive enzymes directly into their prey. Mites and ticks have a range of chelicerae. Carnivores have chelicerae that tear and crush prey, whereas herbivores can have chelicerae that are modified for piercing and sucking (as do parasitic species). In sea spiders, the chelicerae (also known as chelifores) are short and chelate and are positioned on either side of the base of the proboscis or sometimes vestigial or absent.
Pedipalps
In addition to chelicerae, arachnids also possess a pair of pedipalpPedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...
s. In scorpions, the pedipalps are large and chelate (of the scissor type at Figure 4). They are used to capture and hold prey items for stinging before the chelicerae tear the prey into items for digestion. In spiders, the pedipalps of males are modified and function as secondary sex organs (transmission of sperm to the female). The pedipalps of mites and ticks vary depending on the species' feeding mode. They are segmented and may be leg-like or chelate, like a second pair of chelicerae.