Dictionary:

arthropod

  (är'thrə-pŏd')

Any of numerous invertebrate animals of the phylum Arthropoda, including the insects, crustaceans, arachnids, and myriapods, that are characterized by a chitinous exoskeleton and a segmented body to which jointed appendages are articulated in pairs.

[From New Latin Arthropoda, phylum name : ARTHRO– + New Latin -poda, -pod.]

(click to enlarge)
Representative arthropods. Uniramia, the largest of the arthropod subphyla, contains mostly … (credit: © Merriam-Webster Inc.)

Any member of the largest phylum, Arthropoda, in the animal kingdom. Arthropoda consists of more than one million known invertebrate species in four subphyla: Uniramia (five classes, including insects), Chelicerata (three classes, including arachnids and horseshoe crabs), Crustacea (crustaceans), and Trilobita (trilobites). All arthropods are bilaterally symmetrical and possess a segmented body covered by an exoskeleton containing chitin, which serves as both armour and a surface for muscle attachment. Each body segment may bear a pair of jointed appendages. The phylum includes carnivores, herbivores, omnivores, detritus feeders, filter feeders, and parasites (see parasitism) in nearly all environments, both aquatic and terrestrial.

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Arthropods are animals with exoskeletons (external skeletons), segmented bodies, and jointed legs. They are the largest group of animals on Earth and include insects, crustaceans, and arachnids. Insects include organisms such as beetles, grasshoppers, and butterflies. They are mostly terrestrial, small in size, and typically herbivorous. Many species of insects are used as food, and they are traditional food sources in many areas of the tropics. Crustaceans include lobsters, crabs, crayfish, and shrimp. They are mostly aquatic animals, and some, like lobsters and crabs, are relatively large animals. (Crustaceans are discussed below, and are covered in further detail in the article "Crustaceans and Shellfish.") Throughout history, the larger crustacean species have been highly prized food sources. Arachnids include spiders and scorpions, some forms of which are used as food.

The arthropod's exoskeleton is a tough cuticle made of chitin that protects the organism and provides anchor points for muscles. The exoskeleton in crustaceans is rich with calcium carbonate and is particularly hard and thick. The exoskeleton limits an organism's ability to grow in size and must be periodically shed (molted) as the organism grows. Most arthropods go through a series of molts and become more adultlike with each succeeding one.

Some insects, like flies, wasps, beetles, and butterflies, go through larval and pupal stages that are quite different from the adult stages of those species. As embryos, these organisms develop into a larva that is relatively immobile and specializes in eating and storing fat. The larva then transforms into a pupa (an intermediate stage between larva and adult), and finally into an adult that is highly mobile and specializes in reproduction. In insects that undergo such a metamorphosis, the larva is generally the largest form and the one that humans typically prefer as food. The advantage, for humans, of consuming larval insects is that during immature stages of development, insects are soft-bodied and typically high in fat; in addition, the larval stage is often the stage of the life cycle in which individual insects can be found in the greatest aggregations. For example, in the order Lepidoptera (butterflies and moths), insects are in their largest form and have the highest energy (caloric) value during the larval stage of the life cycle. In contrast, the adult forms of Lepidoptera have lower body mass, a hardened exoskeleton, and are more mobile and widely dispersed than larvae.

The crustaceans used as food are aquatic animals that are widespread geographically. Shrimp, lobsters, and crabs inhabit marine ecosystems, and crayfish inhabit freshwater ecosystems. Shrimp are the smallest crustacean and range in size from that of a small insect to over twenty centimeters (seven to eight inches). They tend to live close to the bottom, or in midwater, and feed on plants and small animals. They are food for predatory fish like cod, pollock, and flounder. Lobsters, crabs, and crayfish are larger than shrimp and are important benthic (bottom-dwelling) predators in local ecosystems. The American (Homarus americanus) and European (Homarus gammarus) species of lobster are found in the northern Atlantic Ocean. Adults feed on plant material, shellfish, sea urchins, and crabs. They are solitary animals that defend territory around their shelter (spaces under rocks or large crevices), and they are most active in foraging at night. Spiny (rock) lobsters are found in warm tropical and temperate seas. They feed on snails and clams and small crustaceans and are prey for sharks, octopus, and finfish. They lack the larger claws of the American and European lobsters and are gregarious animals that sometimes migrate long distances.

Crabs are the rounder bodied (compared to shrimp and lobsters) crustaceans that walk sideways; some even swim. The species of crab used as food vary in size from less than two pounds for the Dungeness crabs (Cancer magister) to up to twenty-five pounds for the Alaskan king crab (Paralithodes camtschaticus). Adult crabs are omnivores and dominant predators in local food webs. They feed on shellfish, finfish, and other crustaceans, as well as on detritus (debris). Crabs are widely distributed geographically: Species like the gazami crab (Portunus trituberculatus), the swimming crab (Portunus pelagicus), and the blue crab (Callinectus sapidus) are tropical or subtropical in distribution. The snow or queen crab (Cheonoecetes opilio) is found in the cold seas of the North Atlantic and Pacific Oceans and the Sea of Japan. The most spectacular crabs are the king crabs that live off the coast of Alaska. The red king crab (Paralithodes camtschaticus) is the largest: males of this species can grow to up to twenty-five pounds and have a leg span of five feet across. The blue and the golden king crabs (Paralithodes platypus and Lithodes aequispinus) are somewhat smaller than the red king crab, but they are still king-sized.

Crayfish (or crawfish) look somewhat like lobsters, but they inhabit freshwater ecosystems and are primarily temperate in distribution. North America contains the greatest species diversity of crayfish. They feed on aquatic and semiaquatic vegetation, invertebrates, and detritus. North American species range in size from two to three ounces (50 to 80 grams), but much larger species exist in Australia.

History of Consumption

European populations and European-derived populations in North America historically have placed taboos on entomophagous eating practices (the consumption of insects) and continue to do so. This is notwithstanding the repeated attempts by entomologists to make insects more appealing. One of the best-known attempts is Ronald Taylor's 1975 book Butterflies in My Stomach, and the accompanying recipe guide, Entertaining with Insects (1976).

Although entomophagous eating practices have ceased in Europe, insects were at one time frequently eaten throughout the continent. Rural inhabitants of Europe consumed Cockchafer grubs until the 1800s, and these grubs were an important source of protein in Ireland during the famine of 1688. The Greeks and Romans also held some insects in high esteem as a food source. Ancient Greeks considered grasshoppers a delicacy, and even Aristotle wrote of eating cicadas. He considered them tastiest just before the final instar (stage between two molts), but females laden with eggs were also considered to be very good. The Greeks and Romans also ate a large Melolonthid grub, possibly Lucanus cervus, which Pliny wrote was fattened before consumption.

For many other populations the consumption of insects has continued into the early twenty-first century, or not long before that time. In Mexico a well-known example of cuisine involving insects is ahauatle, a mixture of hemiptera eggs, that Francisco Hernandez first described in 1649. The eggs were also dried and used as a condiment in the preparation of a traditional Christmas Eve dish, revoltijo. In Colombia the giant queen ants of the genus Atta are considered a gastronomical delicacy. There the consumption of giant queen ants can be traced to precolonial times: Gonzalo Jimenez de Quesada, founder of the Colombian capital city Santa Fe de Bogotá, first described their use by local peoples in the highlands in 1555.

The consumption of a wide variety of insects has been reported among Amerindian groups in South American rain forests, and insects have probably been part of that region's diet for a very long time. The insects that appear to be consumed most commonly are ants of the genus Atta, palm grubs, and caterpillars of various sorts. The naturalist Alfred Wallace first described the consumption of Atta queen ants in 1854:

They are eaten alive; the insect being held by the head as we hold a strawberry by its stalk, and the abdomen being bitten off, the body, wings and legs are thrown down to the floor, where they continue to crawl along apparently unaware of the loss of their posterior extremities.

Palm grubs, the large, fatty, legless larvae of wood-boring weevils (Rhynchophorus) found in the pith of felled palm trees, are a highly esteemed food among Amerindians. Bancroft, writing in the eighteenth century, claimed that palm grubs were equally highly esteemed by Europeans in Surinam, particularly by the French.

In Africa the use of insects as food is quite widespread and probably has deep historical roots. The mopane worm (Gonimbrasia belina), the so-called snack that crawls, is one of the best known edible caterpillars. Termites are also utilized as food, especially in the early rainy season when the reproductive forms swarm from the nest. At one time, termites were such an important addition to the diet that their mounds were often disputed as property. Locusts (grasshoppers that go into a swarming phase), in particular the desert locust (Schistocerca gregaria), also play a large role in the diet of Africans. In African history the locusts were so popular that people actually welcomed the arrival of swarms.

In the Middle East the desert locust was also a major source of food historically. Perhaps the most well-known incident involving locust eating was John the Baptist's ordeal in the desert during which he survived on locusts (St. John's bread) and honey. By using locusts as food he was observing the decree of Moses, "These ye may eat; the locust after his kind and the bald locust after his kind, and the cricket after his kind and the grasshopper after his kind" (Leviticus 9:22).

In Asia the consumption of insects as food was described from the Chung-Qiu dynasty (770–475 B.C.E.) and continues to the present day. The most commonly consumed food insects in that region are bee brood (larvae and pupae), beetles such as Dytiscid and Hydrophilid beetles, and the giant water beetle (Lethocerus indicus), the larvae of weevils like Rhynchophorus, and locusts of the genera Oxya and Locusta. Perhaps the most well-known insect eaten in the region is the pupa of the silkworm Bombyx mori.

In Australia the black honey ant (Camponotus inflatus) is a highly sought-after food of Aboriginal Australians and is even considered a totem animal by some clans. It is similar to the honey ant found throughout North and Central America: a modified worker ant with an enlarged body the size of a grape that is full of nectar. Digging up these ants is still considered an important traditional practice and is still taught to children. Witchetty grubs were also an important food of Australian Aborigines. The name witchetty grub refers to any number of root-boring larvae and probably includes Cossid moth larvae (Xyleutes leuchomochla), giant ghost moth larvae (Hepialidae), and longicorn beetle larvae (Cerambycidae). One of the most unique and well-documented examples of entomophagous eating habits in Australia was the annual feast of bugong moths (Agrotis infusa), which occurred until the 1890s. These moths migrate from the plains to aestivate (the summer equivalent of hibernation) in the rock crevices of the Bugong Mountains. Aboriginal Australians from many different tribes traditionally gathered to feast on them. Evidence of these feasts has been carbon-dated as early as 1000 C.E.

Procurement and Capture

The harvesting of insects varies greatly by species because it is tailored to the ecological and behavioral characteristics of different species, as well as the stage of the life cycle sought. Harvesting is typically done for subsistence or to satisfy the demands of a local market.

The harvesting of larval forms like grubs and caterpillars is relatively easy as long as the food source is known. Caterpillars like mopane worms can be picked from their host trees (mopane trees), or for species like the Pandora moth (Colorado Pandora lindseyi), gathered as they descend from their host trees to pupate in the soil. The larva of wood-boring weevils like Rhynchophorus can be harvested by splitting open the palm trees they inhabit, and the larva of root-boring grubs like wichetty grubs can be harvested from the roots of their host plant.

Harvesting mobile adults is more of a challenge. One strategy is to harvest at a point of high aggregation. The giant queen ants of the genus Atta can be collected as they swarm from the nest on nuptial flights early in the rainy season. Some termites, like Macrotermes, can be harvested in the same way. The bogong moths are smoked out of the rock crevices where they gather to aestivate. Social insects that live in large colonies, like ants and termites, can be dug out or lured out by intruding smoke or by inserting a probe, which the soldiers defending the colony will attack. At least one arachnid, the tarantula, can also be attracted out of its burrow using a probe.

Another strategy is to create an aggregation. For grasshoppers and crickets this is done by surrounding them by hunters carrying sticks and driving them into holes or trenches. They can also be captured by dragging bags or nets along the ground and collecting them. A third strategy is to attract the insects to a flame or a light. One species of giant queen ants, as well as some termites and dragonflies, can be attracted to a flame that conveniently singes their wings and makes them very easy to collect. At lease one species of beetle can be attracted to a black light.

Preparation and Consumption

In areas where insects are a traditional part of the diet, they are typically consumed raw or are prepared like other foods, especially other animal food. For example, in Japan grasshoppers, silkworm pupae, and bee pupae are cooked in soy sauce and sugar and served as appetizers. In other parts of Asia, larvae of various sorts, beetles, scorpions, and tarantulas are served fried or stir-fried with vegetables and typical seasonings. In Africa, mopani worms are eaten raw, fried, or cooked in a typical stew after they have been squeezed to remove gut contents.

In general, soft-bodied forms like larvae and pupae are typically fried, grilled, or stewed with local vegetables and seasonings. Larger, hard-bodied forms (such as adults with exoskeletons) like grasshoppers and locusts are typically soaked or cooked in salted water and then sun-dried, or even grilled like shrimp. The legs and wings are typically removed before they are consumed. The exoskeleton of these organisms is retained and provides a certain crunchiness. Smaller organisms with exoskeletons, like ants and termites, are often roasted or fried. In the past, Native North Americans roasted both grasshoppers and crickets and pounded them together with seeds and berries to make a cake called a "desert fruitcake," which could be sun-dried and stored.

Relations to Human Biology

Arthropods are animals and are therefore generally comparable to other animal foods in terms of their nutritional composition. Insects have protein content similar to that of meats like beef and pork. The quality of the protein, however, appears to vary greatly among species; in most cases it is better in terms of amino acid composition than that of plant foods like grains and legumes. The larval stages of arthropods like palm grubs and wichetty grubs are quite high in fat and are similar in that regard to U.S.-style hot dogs. Caterpillars tend to be more muscular and, hence, higher in protein. In terms of micronutrients, insects generally have reasonable quantities of iron, calcium, and B vitamins. As mentioned earlier, the crunchy exoskeleton of insects like grasshoppers is partially composed of chitin, a substance not digested by humans. Little is known about the potential toxic or anti-nutritional factors of insects, although in areas where pesticides are used, toxicity may be of serious concern for all species.

Contemporary Issues

There is a worldwide general trend towards the reduction of entomophagous eating practices. This may be due to the increased use of pesticides to control insects in agricultural zones or the trend toward the adoption of westernized diets (in other words, diets like those of North Americans and Europeans) in which insects have extremely low status as food or are taboo. Despite the general reduction in the consumption of insects as food, there have been efforts to commercialize some food insects. Entrepreneurs in Australia have introduced some local delicacies like black honey ants, witchetty grubs, bardi grubs (the larvae of a Cerambycid beetle), and Trigona bees to the commercial food market, and some Australian restaurants include insects on their menus. Entrepreneurs in South Africa market mopani worms, and the appearance of caterpillars as ingredients has been a general trend on menus in Africa. Some Asian countries also export food insects as specialty items: Thailand exports frozen steamed ant larvae and pupae, Korea exports pupa of the silkworm Bombyx mori, and Japan exports bee pupae in soy to the United States.

There has also been research and development into the rearing of insects as "mini-livestock" in order to meet the subsistence needs, especially the protein needs, of impoverished rural populations. The idea of purposefully raising insects for food is not as far-fetched as it might seem: for example, many societies have been raising bees for a long time.

Bibliography

Caddy, John F., ed. Marine Invertebrate Fisheries: Their Assessment and Management. New York: John Wiley and Sons, 1989.

Chaffin, Yule. Alaska's Southwest: Koniag to King Crab. Anchorage: Chaffin, 1967.

DeFoliart, Gene R. "Insects as Food: Why the Western Attitude Is Important." Annual Review of Entymology 44 (1999): 21–50.

Goddard, J. S. "Food and Feeding." In Freshwater Crayfish: Biology, Management and Exploitation, edited by D. M. Holdich and R. S. Lowery. London and North Ryde: Croom Helm, 1988. Portland, Ore.: Timber Press, 1988.

Paoletti, Maurizio, and Sandra G. F. Bukkens, eds. "Minilive-stock." Special issue of Ecology of Food and Nutrition 36, no. 2–4 (1997).

Phillips, B. F., and J. Kittaka, eds. Spiny Lobsters: Fisheries and Culture. 2d ed. Malden, Mass.: Fishing News Books, 2000.

Pitre, Glen. The Crawfish Book: The Story of Man and Mudbugs Starting in 25,000 B.C and Ending With the Batch Just Put on to Boil. Jackson: University Press of Mississippi, 1993.

Tannahill, Reay. Food in History. New York: Stein and Day, 1973.

Taylor, Ronald L. Butterflies in My Stomach. Santa Barbara, Calif.: Woodbridge Press, 1975.

Taylor, Ronald L., and Barbara J. Carter. Entertaining with Insects. Santa Barbara, Calif.: Woodbridge Press, 1976.

Toussaint-Samat, Maguelonne. A History of Food, translated by Anthea Bell. Paris: Bordas, 1987. New York: Barnes and Noble, 1998.

—Darna L. Dufour

A phylum, or major division of the animal kingdom. Arthropods are animals with jointed legs and segmented bodies, such as insects, spiders, centipedes, and crustaceans. There are more species of arthropods than of any other animal phylum.

Pertaining to or emanating from arthropods.

• a. allergy — see allergy.
• a. ectoparasites — insects that parasitize the skin of animals.

Arthropoda Fossil range: Cambrian or earlier - Recent
Mexican redknee tarantula Brachypelma smithi
Scientific classification
Kingdom: Animalia Superphylum: Ecdysozoa Phylum: Arthropoda Latreille, 1829
Subphyla and Classes
Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. Merostomata - horseshoe crabs, etc. Pycnogonida - sea spiders Eurypterida - sea scorpions (extinct) Subphylum Myriapoda Chilopoda - centipedes Diplopoda - millipedes Pauropoda Symphyla Subphylum Hexapoda Insecta - insects Collembola - springtails Diplura Protura Subphylum Crustacea Branchiopoda – brine shrimp etc. Remipedia Cephalocarida – horseshoe shrimp Maxillopoda - barnacles, fish lice, etc. Ostracoda – seed shrimp Malacostraca - lobsters, crabs, shrimp, etc.

Arthropods (Phylum Arthropoda, from Greek ἄρθρον, "joint", and ποδός, "foot") are the largest phylum of animals and include the insects, arachnids, crustaceans, and others. Arthropods are characterised by the possession of a segmented body with appendages on each segment. They have a dorsal heart and a ventral nervous system. All arthropods are covered by a hard exoskeleton made of chitin, a polysaccharide, which provides physical protection and resistance to desiccation. Periodically, an arthropod sheds this covering when it moults.

More than 80% of described living animal species are arthropods,^[1] with over a million modern species described and a fossil record reaching back to the late proterozoic era. Arthropods are common throughout marine, freshwater, terrestrial, and even aerial environments, as well as including various symbiotic and parasitic forms. They range in size from microscopic plankton (~¼ mm) up to forms several metres long. The largest living arthropod is the Japanese spider crab, with a leg span up to 3½ m (12 ft), and some prehistoric arthropods were even larger, such as Pterygotus and Arthropleura.

Basic arthropod structure

Blue crab (Callinectes sapidus), a crustacean

The success of arthropods is related to their hard exoskeleton, segmentation, and jointed appendages. The appendages are used for feeding, sensory reception, defense, and locomotion. The muscle system is more or less assisted by hydraulics originated from the blood pressure created by the heart&nbsp.^[2] The hydraulic system in spiders is especially well developed.

Harpaphe haydeniana, a myriapod

Mating water striders and their shadows

Aquatic arthropods use gills to exchange gases. These gills have an extensive surface area in contact with the surrounding water. Terrestrial arthropods have internal surfaces that are specialised for gas exchange. Insects and most other terrestrial species have tracheal systems: air sacs leading into the body from pores called spiracles in the epidermis cuticle. Others use book lungs, or gills modified for breathing air as seen in species like the coconut crab. Some areas of the legs of soldier crabs are covered with an oxygen absorbing membrane. The gill chambers in terrestrial crabs sometimes have two different structures: one that is gilled and used for breathing underwater, and another specially adapted to take up oxygen from the air (a pseudolung). Arthropods also have a complete digestive system with both a mouth and anus.

Arthropods have an open circulatory system. Haemolymph containing haemocyanin, a copper-based oxygen-carrying protein (the copper makes the blood blue, unlike humans that use hemoglobin which uses iron that makes it red), is propelled by a series of hearts into the body cavity where it comes in direct contact with the tissues. Arthropods are protostomes. There is a coelom, but it is reduced to a tiny cavity around the reproductive and excretory organs, and the dominant body cavity is a haemocoel, filled with haemolymph which bathes the organs directly. The arthropod body is divided into a series of distinct segments, plus a pre-segmental acron which usually supports compound and simple eyes and a post-segmental telson. These are grouped into distinct, specialised body regions called tagmata. Each segment, at least primitively, supports a pair of appendages.

The cuticle in arthropods forms a rigid exoskeleton, composed mainly of chitin, which is periodically shed as the animal grows. They contain an inner zone (procuticle) which is made of protein and chitin and is responsible for the strength of the exoskeleton. The outer zone (epicuticle) lies on the surface of the procuticle. It is nonchitinous and is a complex of proteins and lipids. It provides the moisture proofing and protection to the procuticle. The exoskeleton takes the form of plates called sclerites on the segments, plus rings on the appendages that divide them into segments separated by joints. This is in fact what gives arthropods their name — jointed feet — and separates them from their relatives, the Onychophora and Tardigrada, also called Lobopoda (and which is sometimes included in a group called Panarthropoda that also includes arthropods). The exoskeletons of arthropods strengthen them against attack by predators and are impermeable to water. In order to grow, an arthropod must shed its old exoskeleton and secrete a new one. This process, ecdysis, is expensive in terms of energy, and during the moulting period, an arthropod is vulnerable.

Classification of arthropods

Arthropoda Paradoxopoda  Myriapoda Chelicerata Pancrustacea    Cirripedia Remipedia Collembola       Branchiopoda Cephalocarida Malacostraca Insecta Phylogenetic relationships of the major extant arthropod groups, derived from mitochondrial DNA sequences&nbsp.[3] Taxa in pink are parts of the subphylum Crustacea.

Arthropods are typically classified into five subphyla, of which one is extinct:^[4]

1. Trilobites are a group of formerly numerous marine animals that died in the mass extinction at the end of the Permian-Triassic extinction event.
2. Chelicerates include spiders, mites, scorpions and related organisms. They are characterised by the presence of chelicerae.
3. Myriapods comprise millipedes and centipedes and their relatives and have many body segments, each bearing one or two pairs of legs. They are sometimes grouped with the hexapods.
4. Hexapods comprise insects and three small orders of insect-like animals with six thoracic legs. They are sometimes grouped with the myriapods, in a group called Uniramia, though genetic evidence tends to support a closer relationship between hexapods and crustaceans.
5. Crustaceans are primarily marine (a notable exception being woodlice) and are characterised by having biramous appendages. They include lobsters, crabs, barnacles, and many others.

Aside from these major groups, there are also a number of fossil forms - mostly from the lower Cambrian - including anomalocarids, euthycarcinoids ^[5] and Arthrogyrinus which are difficult to place, either from lack of obvious affinity to any of the main groups or from clear affinity to several of them.

The phylogeny of the arthropods has been an area of considerable interest and dispute. The validity of many of the arthropod groups suggested by earlier authors is being questioned by recent studies; these include Mandibulata, Uniramia and Atelocerata. The most recent studies tend to suggest a paraphyletic Crustacea with different hexapod groups nested within it&nbsp.^[3][6] The remaining clade of Myriapoda and Chelicerata is referred to as Paradoxopoda or Myriochelata.

Since the International Code of Zoological Nomenclature recognises no priority above the rank of family, many of the higher groups can be referred to by a variety of different names&nbsp.^[7]

Evolution

A velvet worm

Sipuncula Articulata  Mollusca Euarticulata  Annelida Panarthropoda  Onychophora Tardigrada Arthropoda A phylogeny of the arthropods after Nielsen.[8]

Arthropods are today almost universally considered to be monophyletic, i.e. they only arose once, a view supported by both morphological and molecular studies. Such a view contradicts the widespread view in the 1970s that the arthropods had evolved on several occasions from soft-bodied, annelid-like ancestors.

The closest relatives of the arthropods are usually considered to be the Tardigrada and Onychophora, together forming the monophyletic group Panarthropoda (the crustaceans, myriapods, chelicerates and insects are often referred to as "Euarthropoda" to distinguish them from their soft-bodied relatives). Comparison between these groups suggests that the euarthropods evolved from a soft-bodied ancestor not too dissimilar to the living onychophorans, a view that has found some support from the fossil record.

Traditionally the Annelida have been considered the closest relatives of these three phyla, on account of their common segmentation. Molecular data however, are strongly against this grouping (known as the Articulata), suggesting instead that the panarthropods belong in a clade including both the arthropods and various pseudocoelomates such as roundworms and priapulids that share with them growth by moulting, or ecdysis, from which its name, the Ecdysozoa. is derived. If this new grouping is correct, then segmentation of arthropods and annelids has either evolved through convergence, or has been inherited from a very deep ancestor, and has been subsequently lost in several other lineages, such as the non-arthropod members of the Ecdysozoa.

References

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Arthropoda

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Wikibooks' Dichotomous Key has more about this subject:

Arthropoda

1. ^ Anna Thanukos. The Arthropod Story. University of California, Berkeley.
2. ^ "Do spiders have hydraulic legs?", The Straight Dope, 2004-09-27. 
3. ^ ^{a b} Alexandre Hassanin (2006). Phylogeny of Arthropoda inferred from mitochondrial sequences: Strategies for limiting the misleading effects of multiple changes in pattern and rates of substitution. Molecular Phylogenetics and Evolution 38: 100–116. 
4. ^ Arthropoda (TSN 82696). Integrated Taxonomic Information System. Accessed on August 15 2006.
5. ^ The Rhynie Chert Euthycarcinoids. University of Aberdeen. Retrieved on 2006-08-15.
6. ^ Giribet, G., S. Richter, G. D. Edgecombe & W. C. Wheeler (2005). The position of crustaceans within Arthropoda — Evidence from nine molecular loci and morphology. Crustacean Issues 16: 307–352. 
7. ^ Campbell, Reece & Mitchell (2006-07-30). Arthropoda.
8. ^ Nielsen, C. (2001). Animal Evolution: Interrelationships of the Living Phyla. Second Edition. Oxford University Press, Oxford. ISBN 978-0-19-850681-2. 

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