The evolutionary ancestry of arthropods dates back to the Cambrian period. The group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians (or their constituent clades) in a superphylum Ecdysozoa. Overall, however, the basal relationships of animals are not yet well resolved. Likewise, the relationships between various arthropod groups are still actively debated. Today, arthropods contribute to the human food supply both directly as food, and more importantly, indirectly as pollinators of crops. Some species are known to spread severe disease to humans, livestock, and crops. (Full article...)
Fossil specimen (holotype) on display at the Smithsonian in Washington, D.C.
Opabinia regalis is an extinct, stem grouparthropod found in the Middle CambrianBurgess ShaleLagerstätte (505 million years ago) of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed, where they constitute less than 0.1% of the community.
When the first thorough examination of Opabinia in 1975 revealed its unusual features, it was thought to be unrelated to any known phylum, or perhaps a relative of arthropod and annelid ancestors. However, later studies since late 1990s consistently support its affinity as a member of basal arthropods, alongside the closely related radiodonts (Anomalocaris and relatives) and gilled lobopodians (Kerygmachela and Pambdelurion).
In the 1970s, there was an ongoing debate about whether multi-celled animals appeared suddenly during the Early Cambrian, in an event called the Cambrian explosion, or had arisen earlier but without leaving fossils. At first Opabinia was regarded as strong evidence for the "explosive" hypothesis. Later the discovery of a whole series of similar lobopodian animals, some with closer resemblances to arthropods, and the development of the idea of stem groups, suggested that the Early Cambrian was a time of relatively fast evolution, but one that could be understood without assuming any unique evolutionary processes. (Full article...)
Grasshoppers are a group of insects belonging to the suborderCaelifera. They are amongst what are possibly the most ancient living groups of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago.
Grasshoppers are typically ground-dwelling insects with powerful hind legs which allow them to escape from threats by leaping vigorously. Their front leg is shorter and used for grasping food. As hemimetabolous insects, they do not undergo complete metamorphosis; they hatch from an egg into a nymph or "hopper" which undergoes five moults, becoming more similar to the adult insect at each developmental stage. The grasshopper hears through the tympanal organ which can be found in the first segment of the abdomen attached to the thorax; while its sense of vision is in the compound eyes, the change in light intensity is perceived in the simple eyes (ocelli). At high population densities and under certain environmental conditions, some grasshopper species can change colour and behavior and form swarms. Under these circumstances, they are known as locusts.
Grasshoppers are plant-eaters, with a few species at times becoming serious pests of cereals, vegetables and pasture, especially when they swarm in the millions as locusts and destroy crops over wide areas. They protect themselves from predators by camouflage; when detected, many species attempt to startle the predator with a brilliantly coloured wing flash while jumping and (if adult) launching themselves into the air, usually flying for only a short distance. Other species such as the rainbow grasshopper have warning coloration which deters predators. Grasshoppers are affected by parasites and various diseases, and many predatory creatures feed on both nymphs and adults. The eggs are subject to attack by parasitoids and predators. Grasshoppers are diurnal insects—meaning, they are most active during the day time. (Full article...)
Forfarella was very small, only reaching 1.7 centimetres (0.67 inches) of length. It had a nearly rectangular head, with its eyes being unknown but possibly represented by a tubercle in the fossil. Its abdomen consisted of an almost trapezoidal preabdomen and a long, tapering postabdomen. The telson (the posteriormost division of the body) is not preserved, but it was probably short. The appendages, known only from a few fragments, probably had swimming paddles that Forfarella used to swim actively.
The fossil of Forfarella was purchased in 1893 from a fossil collection. It was sent to the Natural History Museum in London. Decades later, in 1962, a paleontologist studied it and determined that it was a chasmataspidid, naming it Forfarella mitchelli. However, the paleontologist never formally published his findings. It would not be until 1999 when a group of three other paleontologists formally described Forfarella. Forming part of the familyDiploaspididae, it was similar to Diploaspis and other Devonian genera, although it is speculated that Forfarella may have existed during the Silurian as well. It was a lacustrine animal, meaning that it lived in lakes. (Full article...)
Puzzled by the geographical distribution of wildlife and fossils he collected on the voyage, Darwin began detailed investigations and, in 1838, devised his theory of natural selection. Although he discussed his ideas with several naturalists, he needed time for extensive research, and his geological work had priority. He was writing up his theory in 1858 when Alfred Russel Wallace sent him an essay that described the same idea, prompting immediate joint submission of both their theories to the Linnean Society of London. Darwin's work established evolutionary descent with modification as the dominant scientific explanation of diversification in nature. In 1871, he examined human evolution and sexual selection in The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals (1872). His research on plants was published in a series of books, and in his final book, The Formation of Vegetable Mould, through the Actions of Worms (1881), he examined earthworms and their effect on soil. (Full article...)
Eysyslopterus is a little-known basal genus that was distinguished from the rest of adelophthalmids by the position near the head margin of the eyes, different from the rest of its relatives. Its carapace was parabolic (approximately U-shaped) and with transverse deep furrows forming the ornamentation. With an estimated length of 8 cm (3.1 in), Eysyslopterus was a small eurypterid. It lived in a nearshorelagoonal quiet community along other eurypterid species. (Full article...)
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Fossil specimen of A. mansfieldi illustrated by James Hall
Adelophthalmus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Adelophthalmus have been discovered in deposits ranging in age from the Early Devonian to the Early Permian, which makes it the longest lived of all known eurypterid genera, with a total temporal range of over 120 million years. Adelopththalmus was the final genus of the Eurypterina suborder of eurypterids and consisted the only known genus of swimming eurypterids from the Middle Devonian until its extinction during the Permian, after which the few surviving eurypterids were all walking forms of the suborder Stylonurina.
Fossils of Adelophthalmus have been described from four continents; North America, Europe, Asia and Australia, which indicates that Adelophthalmus might have had a nearly cosmopolitan (worldwide) distribution, one of few eurypterid genera to achieve one besides potentially Pterygotus. The territorial expansion of Adelophthalmus had begun early, with representatives found in both Siberia and Australia during the Devonian, but it first gained its almost cosmopolitan distribution following the amalgamation of the supercontinent Pangaea during the Carboniferous and Permian.
The generic name Adelophthalmus means "no obvious eye", referencing that the holotype fossil seemingly represented an eyeless eurypterid, with a carapace (head plate) completely lacking any indication of eyes. Though this has caused much subsequent confusion, including the naming of several junior synonyms, the apparent eyelessness of the type specimen is treated by modern researchers as a preservational artifact, and not a feature that any species of Adelophthalmus would have possessed in life. (Full article...)
Terropterus was the earliest known and largest mixopterid eurypterid. Fossil specimens referred to T. xiushanensis are estimated to have reached up to 40 centimeters (15.7 in) in length, but other fossils, either representing older T. xiushanensis or a second species of Terropterus, demonstrate that members of the genus could reach upwards of at least 100 centimeters (3.3 ft) in length. Terropterus is the only mixopterid known from the ancient southern continent of Gondwana, with the other two mixopterid genera, Mixopterus and Lanarkopterus, only being known from what was once the northern continent of Laurussia. The discovery of Terropterus significantly expanded the known geographical and temporal ranges of the Mixopteridae.
The deposits in which fossils of Terropterus were discovered were once a marine environment. Fossils of several other groups are known from the same deposits, including trilobites, brachiopods, gastropods and other eurypterids. Due to its large size and its predatory adaptations, including the characteristic mixopterid large and spiny forward-facing appendages, Terropterus was likely the apex predator of its marine ecosystem. (Full article...)
Eucteniza (/juːktəˈnaɪzə/yook-tə-NY-zə) is a genus of trapdoor spiders in the family Euctenizidae containing at least 14 species occurring in Mexico and the southern United States. Species are distinguished by a softened rear portion of the carapace, and males possess large spines on the first two pairs of walking legs that are used to hold females during mating. Like other trapdoor spiders they create burrows with a hinged lid, from which they await passing insects and other arthropods to prey upon. Many species are known from only one or two localities, or from only male specimens. More species are expected to be discovered. Eucteniza is closely related to spiders of the genera Entychides and Neoapachella. (Full article...)
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The caddisflies, or orderTrichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the basis of the adult mouthparts. Integripalpian larvae construct a portable casing to protect themselves as they move around looking for food, while annulipalpian larvae make themselves a fixed retreat in which they remain, waiting for food to come to them. The affinities of the small third suborder Spicipalpia are unclear, and molecular analysis suggests it may not be monophyletic. Also called sedge-flies or rail-flies, the adults are small moth-like insects with two pairs of hairy membranous wings. They are closely related to the Lepidoptera (moths and butterflies) which have scales on their wings; the two orders together form the superorder Amphiesmenoptera.
The aquatic larvae are found in a wide variety of habitats such as streams, rivers, lakes, ponds, spring seeps and temporary waters (vernal pools), and even the ocean. The larvae of many species use silk to make protective cases, which are often strengthened with gravel, sand, twigs, bitten-off pieces of plants, or other debris. The larvae exhibit various feeding strategies, with different species being predators, leaf shredders, algal grazers, or collectors of particles from the water column and benthos. Most adults have short lives during which they do not feed.
In fly fishing, artificial flies called dry flies are tied to imitate adults, while larvae and pupae are imitated with artificial flies called wet flies or nymphs. It is also possible to use them as bait, though this is not as common as artificial flies and is known as bait fishing. Common and widespread genera such as Helicopsyche and Hydropsyche are important in the sport, where caddisflies are known as "sedges". Caddisflies are useful as bioindicators, as they are sensitive to water pollution and are large enough to be assessed in the field. In art, the French artist Hubert Duprat has created works by providing caddis larvae with small grains of gold and precious stones for them to build into decorative cases. (Full article...)
Paleomerus is one of the oldest arthropods, being sometimes interpreted as the model of the first arachnomorphs. It is part of the order Strabopida, a poorly known group closely related to the aglaspidids of uncertain affinities, often being ignored by researchers and authors due to the poor preservation and abundance of their fossils. It has been suggested that Paleomerus and the closely related Strabops could be synonymous with each other, since they differ only in the size of the telson (the posteriormost division of the body) and the position of the eyes. These two genera were originally deferred by a hypothetical twelfth segment in Paleomerus, but after the discovery and description of a fourth specimen of P. hamiltoni, it has been shown that this segment actually represents the tail of the animal. (Full article...)
The spotted lanternfly's life cycle is often centered on its preferred host, Ailanthus altissima, but L. delicatula can associate with more than 173 plants. Early life stages (instars) of the spotted lanternfly are characterized by spotted black and white nymphs that develop a red pigmentation and wings as they mature. Early life instars have a large host range that narrows with maturation. Adult spotted lanternflies have a black head, grey wings, and red hind wings. Adults do not have any specialized feeding associations with herbaceous plants but cause extensive damage to crops and ornamental plants. The piercing wounds caused by their mouthparts and the honeydew waste they excrete are harmful to the health of host plants. Spotted lanternflies lay egg masses containing 30–50 eggs, often covered with a grayish mud-like coating.
The species was introduced into South Korea in 2006 and Japan in 2009, and has since been considered a pest. In September 2014, L. delicatula was first recorded in the United States, and it is an invasive species in much of the Northeastern United States and is rapidly spreading south and west. L. delicatula's egg masses are the primary vector of spread, with Ailanthus altissima populations seen as a risk factor for further infestation globally. Ongoing pest control efforts have sought to limit population growth, due to the threat L. delicatula poses to global agricultural industries. (Full article...)
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Great frigatebirds (Fregata minor) chasing a red-footed booby (Sula sula) to steal its food Kleptoparasitism (originally spelt clepto-parasitism, meaning "parasitism by theft") is a form of feeding in which one animal deliberately takes food from another. The strategy is evolutionarily stable when stealing is less costly than direct feeding, such as when food is scarce or when victims are abundant. Many kleptoparasites are arthropods, especially bees and wasps, but including some true flies, dung beetles, bugs, and spiders. Cuckoo bees are specialized kleptoparasites which lay their eggs either on the pollen masses made by other bees, or on the insect hosts of parasitoid wasps. They are an instance of Emery's rule, which states that insect social parasites tend to be closely related to their hosts. The behavior occurs, too, in vertebrates including birds such as skuas, which persistently chase other seabirds until they disgorge their food, and carnivorous mammals such as spotted hyenas and lions. Other species opportunistically indulge in kleptoparasitism. (Full article...)
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Dryomyza anilis
Dryomyza anilis is a common fly from the familyDryomyzidae. The fly is found through various areas in the Northern hemisphere and has brown and orange coloration with distinctive large red eyes. The life span of the fly is not known, but laboratory-reared males can live 28–178 days. D. anilis has recently been placed back in the genus Dryomyza, of which it is the type species. Dryomyzidae were previously part of Sciomyzidae but are now considered a separate family with two subfamilies.
Male D. anilis engage in territorial behavior, guarding carcasses to attract potential mates. Males also guard females, and conflicts over females are frequent. Females typically mate with multiple males. Mating occurs through several rounds of copulation and egg-laying. During mating, males engage in a series of "tapping" rituals where they use their claspers to tap the female's genitals, increasing the chance of them fertilizing the female's eggs. Females lay several batches of eggs on carcasses, fungi, and excrement as well as other substrates. (Full article...)
The following are images from various arthropod-related articles on Wikipedia.
Image 1 This fully-grown robber crab has tough fabric forming its joints, delicate biomineralized cuticle over its sensory antennae, optic-quality over its eyes, and strong, calcite-reinforced chitin armouring its body and legs; its pincers can break into coconuts (from Arthropod exoskeleton)
Image 2Decapods, from Ernst Haeckel's 1904 work Kunstformen der Natur (from Crustacean)
Image 3Ghost crab, showing a variety of integument types in its exoskeleton, with transparent biomineralization over the eyes, strong biomineralization over the pincers, and tough chitin fabric in the joints and the bristles on the legs (from Arthropod exoskeleton)
Image 6Formation of anterior segments across arthropod taxa based on gene expression and neuroanatomical observations, Note the chelicera(Ch) and chelifore(Chf) arose from somite 1 and thus correspond to the first antenna(An/An1) of other arthropods. (from Chelicerata)
Image 9Mature queen of a termite colony, showing how the unsclerotised cuticle stretches between the dark sclerites that failed to stretch as the abdomen grew to accommodate her ovaries (from Arthropod exoskeleton)
Image 10Some of the various hypotheses of myriapod phylogeny. Morphological studies (trees a and b) support a sister grouping of Diplopoda and Pauropoda, while studies of DNA or amino acid similarities suggest a variety of different relationships, including the relationship of Pauropoda and Symphyla in tree c. (from Myriapoda)
Image 23In honeypot antrepletes, the abdomens of the workers that hold the sugar solution grow vastly, but only the unsclerotised cuticle can stretch, leaving the unstretched sclerites as dark islands on the clear abdomen (from Arthropod exoskeleton)
Image 25The house centipedeScutigera coleoptrata has rigid sclerites on each body segment. Supple chitin holds the sclerites together and connects the segments flexibly. Similar chitin connects the joints in the legs. Sclerotised tubular leg segments house the leg muscles, their nerves and attachments, leaving room for the passage of blood to and from the hemocoel (from Arthropod exoskeleton)
Image 31This Zoea-stage larva is hardly recognisable as a crab, but each time it sheds its cuticle it remodels itself, eventually taking on its final crab form (from Arthropod exoskeleton)
A honey bee extracts nectar from a flower using its proboscis. Tiny hairs covering the bee's body maintain a slight electrostatic charge, causing pollen from the flower's anthers to stick to the bee's hairs, allowing for pollination when the bee moves on to another flower.
A lithograph by Sidney Hall, published in Urania's Mirror, depicting the constellation Scorpius. One of the 48 constellations identified by the Greek astronomer Ptolemy in the second century, Scorpius lies between Libra to the west and Sagittarius to the east. It contains 18 main stars, the brightest of which is Antares. Although frequently identified as a scorpion, this constellation has also been likened to a "leaning coconut tree" (Java) or "Maui's fishhook" (Hawaii).
Xylotrupes socrates (Siamese rhinoceros beetle, or "fighting beetle"), male, on a banana leaf. This scarab beetle is particularly known for its role in insect fighting in Northern Laos and Thailand.
The orb-weaver spiders (family Araneidae) are the familiar builders of spiral wheel-shaped webs often found in gardens, fields and forests. The family is a large one, including over 2800 species in over 160 genera worldwide, making it the third largest known (behind Salticidae and Linyphiidae). The web has always been thought of as an engineering marvel.
Two Eastern Lubber grasshoppers (Romalea guttata) mating. Native to the southeastern and south central portion of the United States, it is well known both for its size and its unique coloration. During reproduction, the male grasshopper introduces sperm into the ovipositor through its aedeagus (reproductive organ), and inserts its spermatophore, a package containing the sperm, into the female's ovipositor.
A macro shot of the head of a dragonfly, focusing on its compound eyes. Dragonfly eyes have up to 30,000 facets; each one is a separate light-sensing organ or ommatidium, arranged to give nearly a 360° field of vision.
The cryptic mantis (Sibylla pretiosa) is a mantid native to southern Africa. Its common name comes from its ability to grow asymmetrically to match the vegetation of its environment. They have unusual leaf-like projections on the joint of their four walking legs and leaf-like wings, generally the only green portion of the insect's otherwise brown and mottled exoskeleton. Adult females grow to 5–6 cm (2.0–2.4 in) in length while the males are generally about 1 cm smaller.
The citrus root weevil (Diaprepes abbreviatus) is a major agricultural pest weevil in several Caribbean countries and the U.S. state of Florida. The larvae feed on the roots of the host plant for several months. They often eat the taproot of the plant, which can kill it by depriving it of water and nutrients or by making it vulnerable to infection by fungi, or water moulds.
Zonocerus variegatus, the variegated grasshopper, is a species of grasshopper in the family Pyrgomorphidae native to tropical western and central Africa. It feeds on a wide variety of plant foods and causes damage to crops, particularly cassava, groundnuts and vegetables, as well as transmitting diseases caused by mosaic viruses between plants. This Z. variegatus grasshopper was photographed in the Bobiri Forest in Ghana.
The Ozyptila praticola species of crab spider is found throughout Europe and the Middle East. They do not build webs to trap prey, but are active hunters. Crab spiders are so named because of their first two pairs of legs, which are held out to the side giving them a crab-like appearance. Also, like crabs, these spiders move sideways and backwards more easily than forwards.
The red rock crab (Grapsus grapsus), also known as "Sally Lightfoot", is one of the commonest crabs along the western seaboard of the Americas. John Steinbeck wrote of them, "Everyone who has seen them has been delighted with them ... These little crabs, with brilliant cloisonné carapaces, walk on their tiptoes, they have remarkable eyes and an extremely fast reaction time." He tried to catch them but to little avail. "If you walk slowly, they move slowly ahead of you in droves. If you hurry, they hurry. When you plunge at them, they seem to disappear in a puff of blue smoke."
The light blue soldier crab (Mictyris longicarpus) inhabits beaches in the Indo-Pacific region. Soldier crabs filter sand or mud for microorganisms. They congregate during the low tide, and bury themselves in a corkscrew pattern during high tide, or whenever they are threatened.
A female subimago of a March Brown mayfly (Rhithrogena germanica). Mayflies belong to the orderEphemeroptera, and the only insects that have a subimago phase. This stage is a favourite food of many fish, and many fishing flies are modeled to resemble them. They are aquatic insects whose nymph stage usually lasts one year in freshwater. The adults are short-lived, from as little as thirty minutes to a few days depending on the species.
Two flesh-flies (Sarcophaga ruficornis species pictured) mating. The life cycle of the saprophagic flesh-fly larvae has been well researched and is very predictable. Different species prefer bodies in different states of decomposition, which allows forensic entomologists to extrapolate the time of death.
Purana tigrina is a species of cicada found in Southeast Asia. This adult male was photographed in Kadavoor, Kerala, in southern India, and is about one inch (25 mm) in length. The mouthparts are adapted to piercing plant tissues and sucking sap; the male abdomen houses the tymbal, an organ used in the production of song, while the female abdomen is tipped by a large, saw-edged ovipositor.
The western honey bee (Apis mellifera) is the most common of the 7–12 species of honey bee worldwide. It is believed to have originated in either Africa or Asia, and spread naturally through Africa, the Middle East and Europe. Following human introduction into the Americas and Oceania, the species is now found on every continent except Antarctica. Humans have been collecting honey from bees for thousands of years, with evidence in the form of rock art found in France and Spain, dating to around 7000 BC. Along with other insects, the honey bee is an important pollinator, with a large number of the crop species farmed worldwide depending on it.
The Meadow Argus (Junonia villida) is a species of butterfly native to Australasia. Its brown wings are each covered with two distinctive black and blue eyespots as well as white and orange marks that appear on the edge of the wings. Males and females are similar in appearance and size, with females being slightly larger.
The Polyphemus Moth (Anthera polyphemus) is one the biggest moths, having a wingspan of up to 15 cm. Usually found in forests, moths are notable for apparently being attracted to light, the reason for this behaviour is not known.
The Globe Skimmer (Pantala flavescens) is the most widespread dragonfly species on the planet, found between about the 40th parallels of latitude, or where the annual mean temperature is above 20 °C (68 °F), except in Europe where there are only occasional sightings.
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