Portal:Arthropods

The arthropods portal

P:ARTH

An arthropod (/ˈɑːrθrəpɒd/, from Greek ἄρθρον arthron, "joint" and πούς pous, "foot" (gen. ποδός)) 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. Arthropods are bilaterally symmetrical and their body possesses an external skeleton. Some species have wings.

Their versatility has enabled arthropods to become the most species-rich members of all ecological guilds in most environments. They have over a million described species, making up more than 80 percent of all described living animal species, some of which, unlike most other animals, are very successful in dry environments. Arthropods range in size from the microscopic crustacean Stygotantulus up to the Japanese spider crab.

An arthropod's primary internal cavity is a haemocoel, which accommodates its internal organs, and through which its haemolymph – analogue of blood – circulates; it has an open circulatory system. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. Their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong.

Their vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey. Arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many bristles known as setae that project through their cuticles.

Arthropods' methods of reproduction and development are diverse; all terrestrial species use internal fertilization, but this is often by indirect transfer of the sperm via an appendage or the ground, rather than by direct injection. Aquatic species use either internal or external fertilization. Almost all arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother. Arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of maternal care for hatchlings varies from nonexistent to the prolonged care provided by scorpions.

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.

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.

Examples of the five arthropod subphyla

Trilobitomorpha:
Kainops invius

Chelicerata:
Eriophora transmarina

Myriapoda:
Scolopendra cingulata

Hexapoda:
Drosophila melanogaster

Crustacea:
Cancer pagurus

edit

Selected article

Throughout history, there have been many depictions of spiders in popular culture, mythology and symbolism. From Greek mythology to African folklore, the spider has been used in human culture to represent many varied things and indeed endures on into the present day with characters such as Shelob from The Lord of the Rings and Spider-Man from the eponymous comic series. The spider has symbolised patience due to its hunting technique of setting webs and waiting for prey, as well as mischief and malice for its poison and the slow death it causes, its venom often seen as a curse.

Although not all spiders spin webs to hunt prey, they have been attributed by numerous cultures with the origination of basket-weaving, knotwork, weaving, spinning and net making. Web-spinning also caused the association of the spider with creation myths as they seem to have the ability to excrete their own artistic worlds. Spiders have been the focus of fears, stories and mythologies of various cultures for centuries.

Read more...

More articles

edit

Did you know ... ?

... that Glomeris marginata (pictured), a pill millipede, is often confused with the woodlouse Armadillidium, because they both roll themselves up into a ball when disturbed?
... that Mimoides phaon was the first swallowtail butterfly of the genus Mimoides to stray into the United States?
... that the meat of the slipper lobster Ibacus peronii is considered inferior to that of the Moreton Bay bug because it sometimes tastes of garlic?
... that when analyzing relationships of the harvestmen it is found that they are not true spiders, as often believed, but are in fact more closely related to scorpions?
... that the "orchid dupe wasp", Lissopimpla excelsa, ejaculates visible amounts of semen as it tries to copulate with flowers of the leafless, large and tartan tongue orchids, which it mistakes for a female wasp?
... that Tanymastix stagnalis is the only species of fairy shrimp to occur in Ireland?

More facts

edit

Recognised content

Featured articles

Featured lists

Good articles

Featured images

Featured image set: butterfly wing magnifications

Full list of featured images

edit

WikiProjects

WikiProject Tree of Life
- WikiProject Animals
  - WikiProject Arthropods
    - WikiProject Spiders
    - WikiProject Insects
      - WikiProject Lepidoptera

What are WikiProjects?

edit

Selected picture

Dorsal and ventral sides of the large branchiopod Triops longicaudatus.

Credit: Micha L. Rieser

Triops longicaudatus is a freshwater crustacean of the order Notostraca. It is considered a living fossil because its from has changed little from its ancestors 70 million years ago.

Read more...

Gallery

edit

Taxa

Chelicerata: spider · Acari · Opiliones · pseudoscorpion · scorpion · Solifugae · sea spider · Schizomida · Amblypygi · Thelyphonida · Palpigradi · Ricinulei · Xiphosura · †Chasmataspidida · †Eurypterida
Crustacea: Malacostraca (Decapoda – crab, lobster, hermit crab; Amphipoda; Isopoda; mantis shrimp) · Maxillopoda (barnacle; copepod) · Branchiopoda (fairy shrimp; Triops; Daphnia) · ostracod · Remipedia · Cephalocarida
Hexapoda: Entognatha (springtail; Diplura; Protura) · insect (beetle; fly; bee; wasp; ant; butterfly; moth; cockroach; flea; louse; mayfly; dragonfly; damselfly; earwig; mantis)
Myriapoda: centipede · millipede (pill millipede) · Pauropoda · Symphyla · †Arthropleuridea
†Trilobite: †Agnostida · †Asaphida · †Corynexochida · †Harpetida · †Nectaspida · †Redlichiida · †Lichida · †Phacopida · †Proetida · †Ptychopariida

† indicates an extinct taxon.

edit

Topics

Anatomy: antenna · arthropod exoskeleton · arthropod leg · arthropod eye · book lung · chelicerae · differences between butterflies and moths · gill · insect morphology · invertebrate trachea · Malpighian tubule system · mandible · rostrum · simple eye in invertebrates

Study: arachnology · entomology · forensic entomology · glossary of entomology terms · lepidopterist · list of carcinologists · list of entomologists · myrmecology · timeline of entomology

Development: crustacean larvae · ecdysis · exuvia

As food: entomophagy · fried spider · crab fisheries · lobster fishing · shrimp paste

Miscellaneous: arthropod bites and stings · beneficial insects · economic entomology · endangered arthropod · evolution of insects · insectivore

edit

To do

Here are some tasks you can do:

Start a new article. Arthropods cover an huge range of taxa and other topics, so there will always be plenty of missing articles. Some which have been explicitly requested are listed here.
Clean up existing articles. Lists of articles needing cleanup are available either grouped by the work needed or ungrouped.
Expand an existing article. Existing articles are often incomplete and missing information on key aspects of the topic. It is particularly important that the most widely read articles be broad in their scope. Wikipedia:WikiProject Arthropods/Popular pages (updated monthly) shows the number of views each article gets, along with assessments of its quality and importance. Articles with higher importance ratings and greater numbers of views are the priority for article improvements, but almost all our articles would benefit from expansion. Stubs can be found in Category:Arthropod stubs and its subcategories.