In arthropods, the maxillae (singular maxilla) are paired structures present on the head as mouthparts in members of the clade Mandibulata, used for tasting and manipulating food. Embryologically, the maxillae are derived from the 4th and 5th segment of the head and the maxillary palps; segmented appendages extending from the base of the maxilla represent the former leg of those respective segments. In most cases, two pairs of maxillae are present and in different arthropod groups the two pairs of maxillae have been variously modified. In crustaceans, the first pair are called maxillulae (singular maxillula).
An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes insects, arachnids, myriapods, and crustaceans. The term Arthropoda as originally proposed refers to a proposed grouping of Euarthropods and the phylum Onychophora. Arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Arthopods are bilaterally symmetrical and their body possesses an external skeleton. Some species have wings.
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 cutting, chewing, piercing, sucking, shredding, 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.
Mandibulata, termed "mandibulates", is a clade of arthropods that comprises the extant subphyla Myriapoda, Crustacea and Hexapoda. Mandibulata is currently believed to be the sister group of the clade Arachnomorpha, which comprises the rest of arthropods. The mandibulates constitute the largest and most varied arthropod group.
Modified coxae at the base of the pedipalps in spiders are also called "maxillae",although they are not homologous with mandibulate maxillae.
Pedipalps 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") and anterior to the first pair of walking legs.
Spiders are air-breathing arthropods that have eight legs and chelicerae with fangs able to inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of July 2019, at least 48,200 spider species, and 120 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
In biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats, the arms of primates, the front flippers of whales and the forelegs of dogs and horses are all derived from the same ancestral tetrapod structure. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor. The term was first applied to biology in a non-evolutionary context by the anatomist Richard Owen in 1843. Homology was later explained by Charles Darwin's theory of evolution in 1859, but had been observed before this, from Aristotle onwards, and it was explicitly analysed by Pierre Belon in 1555.
In millipedes, the second maxillae have been lost, reducing the mouthparts to only the first maxillae which have fused together to form a gnathochilarium, acting as a lower lip to the buccal cavity and the mandibles which have been enlarged and specialized greatly, used for chewing food. The gnathochilarium is richly infused with chemosensory and tactile receptors along its edge.A pair of maxillary glands, also called nephridial organs, involved in osmoregulation and excreting nitrogenous waste open up to the gnathochilarium and wastes are passed entirely through the digestive tract before being evacuated. The nephridial organs are thought to be derived from similar organs in annelids, although reduced in number since the open circulatory system of arthropods lessens the demand on separate excretory organs. The reason for their anterior location is probably because these organs must be developed early on in the embryo and millipedes and other arthropods develop mainly by proliferation of cells at the posterior of the embryo.
Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name being derived from this feature. Each double-legged segment is a result of two single segments fused together. Most millipedes have very elongated cylindrical or flattened bodies with more than 20 segments, while pill millipedes are shorter and can roll into a ball. Although the name "millipede" derives from the Latin for "thousand feet", no known species has 1,000; the record of 750 legs belongs to Illacme plenipes. There are approximately 12,000 named species classified into 16 orders and around 140 families, making Diplopoda the largest class of myriapods, an arthropod group which also includes centipedes and other multi-legged creatures.
Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration of electrolytes to keep the body fluids from becoming too diluted or concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the osmotic pressure of a solution, the more water tends to move into it. Pressure must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water.
In centipedes, both pairs of maxillae are developed. The first maxillae are situated ventrally to the mandibles and obscure them from view. This pair consists of a basal plate formed from the fused coxae of each leg plus ventral sternite from this segment and is hence called a coxosternite and two pairs of conically jointed appendages called telopodites and coxal projections. The second maxillae, which partly cover the first maxillae, consist of only a telopodite and a coxosternite. The telopodite is recognizably leglike in structure and consists of three segments plus an apical claw. The second maxillae also have a metameric pore, which is the opening of the maxillary gland and maxillary nephridium homologous to those of millipedes.
Centipedes are predatory arthropods belonging to the class Chilopoda of the subphylum Myriapoda, an arthropod group which also includes Millipedes and other multi-legged creatures. Centipedes are elongated metameric creatures with one pair of legs per body segment. Most centipedes are generally venomous and could inflict a painful bite, injecting their venom through pincer-like appendage known as forcipules. Despite the name, centipedes can have a varying number of legs, ranging from 30 to 354. Centipedes always have an odd number of pairs of legs. Therefore, no centipede has exactly 100 legs. Similar to spiders and scorpions, centipedes are predominantly carnivorous.
In crustaceans, the two pairs of maxillae are called maxillulae (1st pair) and maxillae (2nd pair). They serve to transport food to the mandibles but also frequently help in the filtration process and additionally they may sometimes play a role in cleaning and grooming. These structures show an incredible diversity throughout crustaceans but generally are very much flattened and leaf-like. The two pairs are normally positioned very close together and their apical parts generally are in direct contact with the mandible.
Crustaceans form a large, diverse arthropod taxon which includes such familiar animals as crabs, lobsters, crayfish, shrimps, prawns, krill, woodlice, and barnacles. The crustacean group is usually treated as a class under subphylum Mandibulata and because of recent molecular studies it is now well accepted that the crustacean group is paraphyletic, and comprises all animals in the Pancrustacea clade other than hexapods. Some crustaceans are more closely related to insects and other hexapods than they are to certain other crustaceans.
The generalized condition in hexapods is for the first pair of maxillae to consist of a basal triangular sclerite called the cardo and a large central sclerite called the stipes from which arise three processes: the lacinia, the galea and the maxillary palp. The lacinia is often strongly sclerotized and toothed. It functions to cut and manipulate food in the mouth.The galea is a broad, scoop-like, lobe structure, which assists the maxillary palps in sampling items before ingestion. The maxillary palp is serially homologous to the walking leg while the cardo and stipes are regarded by most to be serially homologous to the first leg segment, the coxa. The labium is immediately posterior to the first maxillae and is formed from the fusion of the second maxillae, although in lower orders including the Archaeognatha (bristletails) and Thysanura (silverfish) the two maxillae are not completely fused. It consists of a basal submentum, which connects with the prementum through a narrow sclerite, the mentum. The labium forms the lower portion of the buccal cavity in insects. The prementum has a pair of labial palps laterally, and two broad soft lobes called the paraglossae medially. These paraglossae have two small slender lobes called glossae at their base.
The Archaeognatha are an order of apterygotes, known by various common names such as jumping bristletails. Among extant insect taxa they are some of the most evolutionarily primitive; they appeared in the Middle Devonian period at about the same time as the arachnids. Specimens that closely resemble extant species have been found as both body and trace fossils in strata from the remainder of the Paleozoic Era and more recent periods. For historical reasons an alternative name for the order is Microcoryphia.
Thysanura is the now deprecated name of what was, for over a century, recognised as an order in the class Insecta. The two constituent groups within the former order, the Archaeognatha and the Zygentoma, share several characteristics, such as of having three long caudal filaments, the lateral ones being the cerci, while the one between (telson) is a medial cerciform appendage, specifically an epiproct. They are also both wingless, and have bodies covered with fine scales, rather like the scales of the practically unrelated Lepidoptera. In the late 20th century, it was recognized that the two suborders were not sister taxa, therefore Thysanura was paraphyletic, and the two suborders were each raised to the status of an independent monophyletic order, with Archaeognatha sister taxon to the Dicondylia, including the Zygentoma.
In many hexapods, the mouthparts have been modified for different functions and the maxillae and labium can change in structure greatly. In bees, the maxillae and labium have been modified and fused to form a nectar-sucking proboscis. In the order Hemiptera, the true bugs, plant hoppers, etc., the mouthparts have been modified to form a beak for piercing. The labium forms a sheath around a set of stylets that consist of an outer pair of mandibles and an inner pair of maxillae. In lapping flies, a proboscis is formed from mostly the labium specialized for lapping up liquids. The labial palps form a labella which have sclerotized bands for directing liquid to a hypopharangeal stylet, through which the fly can imbibe liquids. In Lepidopterans, the fluid-sucking proboscis is formed entirely from the galea of the maxillae although labial palps are also present. In Odonata nymphs, the labium forms a mask-like extensible structure, which is used for reaching out and grasping prey.
The maxilla in animals is the upper fixed bone of the jaw formed from the fusion of two maxillary bones. The upper jaw includes the hard palate in the front of the mouth. The two maxillary bones are fused at the intermaxillary suture, forming the anterior nasal spine. This is similar to the mandible, which is also a fusion of two mandibular bones at the mandibular symphysis. The mandible is the movable part of the jaw.
Symphylans, also known as garden centipedes or pseudocentipedes, are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda. Symphylans resemble centipedes, but are smaller, non-venomous, and only distantly related to true centipedes. They can move rapidly through the pores between soil particles, and are typically found from the surface down to a depth of about 50 cm. They consume decaying vegetation, but can do considerable harm in an agricultural setting by consuming seeds, roots, and root hairs in cultivated soil.
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body. An appendage is any of the homologous body parts that may extend from a body segment. These include antennae, mouthparts, gills, walking legs (pereiopods), swimming legs (pleopods), sexual organs (gonopods), and parts of the tail (uropods). Typically, each body segment carries one pair of appendages.
The decapod crustacean, such as a crab, lobster, shrimp or prawn, is made up of 20 body segments grouped into two main body parts, the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various groups these may be reduced or missing. They are, from head to tail:
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa, trochanter, femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus, patella.
This glossary of entomology describes terms used in the formal study of insect species by entomologists.
The Entognatha are a class of wingless and ametabolous arthropods, which, together with the insects, makes up the subphylum Hexapoda. Their mouthparts are entognathous, meaning that they are retracted within the head. Entognatha are apterous, meaning that they lack wings. The class contains three orders: Collembola (springtails), Diplura (“two-tail”) and Protura (“first-tail”), and over 5000 known species. These three groups were historically united with the now-obsolete order Thysanura to form the class Apterygota, but it has since been recognized that the hexapodous condition of these animals has evolved independently from that of insects, and independently within each order. The orders may not be closely related, in which case Entognatha would be a polyphyletic group.
The anatomy of spiders includes many characteristics shared with other arachnids. These characteristics include bodies divided into two tagmata, eight jointed legs, no wings or antennae, the presence of chelicerae and pedipalps, simple eyes, and an exoskeleton, which is periodically shed.
The mandible of an arthropod is a pair of mouthparts used either for biting or cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda, Crustacea and Hexapoda. These groups make up the clade Mandibulata, which is currently believed to be the sister group to the rest of arthropods, the clade Arachnomorpha.
The suboesophageal ganglion of arthropods and in particular insects is part of the arthropod central nervous system (CNS). As indicated by its name, it is located below theoesophagus, inside the head. As part of the ventral nerve cord, it is connected to the brain and to the first thoracic ganglion. Its nerves innervate the sensory organs and muscles of the mouthparts and the salivary glands.
The (pan)arthropod head problem is a long-standing zoological dispute concerning the segmental composition of the heads of the various arthropod groups, and how they are evolutionarily related to each other. While the dispute has historically centered on the exact make-up of the insect head, it has been widened to include other living arthropods such as the crustaceans and chelicerates; and fossil forms, such as the many arthropods known from exceptionally preserved Cambrian faunas. While the topic has classically been based on insect embryology, in recent years a great deal of developmental molecular data has become available. Dozens of more or less distinct solutions to the problem, dating back to at least 1897, have been published, including several in the 2000s.
Insects have a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts. Specialization has mostly been for piercing and sucking, although a range of specializations exist, as these modes of feeding have evolved a number of times. In this page, the individual mouthparts are introduced for chewing insects. Specializations are generally described thereafter.
The external morphology of Lepidoptera is the physiological structure of the bodies of insects belonging to the order Lepidoptera, also known as butterflies and moths. Lepidoptera are distinguished from other orders by the presence of scales on the external parts of the body and appendages, especially the wings. Butterflies and moths vary in size from microlepidoptera only a few millimetres long, to a wingspan of many inches such as the Atlas moth. Comprising over 160,000 described species, the Lepidoptera possess variations of the basic body structure which has evolved to gain advantages in adaptation and distribution.
Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insects from other arthropods: they have a body divided into three regions, have three pairs of legs, and mouthparts located outside of the head capsule. It is this position of the mouthparts which divides them from their closest relatives, the non-insect hexapods, which includes Protura, Diplura, and Collembola.
This glossary describes the terms used in formal descriptions of spiders; where applicable these terms are used in describing other arachnids.
Insects are among the most diverse groups of animals on the planet, including more than a million described species and representing more than half of all known living organisms. The number of extant species is estimated at between six and ten million, found in nearly all environments, although only a small number of species occur in the oceans. This large extant means that the dietary habits of taxa include a large variety of behaviors.
In entomology, the term labellum has been applied variously and in partly contradictory ways. One usage is in referring to a prolongation of the labrum that covers the base of the rostrum in certain Coleoptera and Hemiptera.