Open main menu

The arthropods portal

An arthropod (/ˈɑːrθrəpɒd/, from Greek ἄρθρον arthron, "joint" and πούς pous, "foot") is an invertebrate animal having an exoskeleton (external skeleton), 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.

Their versatility has enabled them 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 per cent 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.

Arthropods' primary internal cavity is a haemocoel, which accommodates their internal organs, and through which their haemolymph – analogue of blood – circulates; they have open circulatory systems. 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 setae (bristles) 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.

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 Metazoa are not yet well resolved. Likewise, the relationships between various arthropod groups are still actively debated. 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.

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.

Selected article

A large mechanical spider on the side of a tall building.
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.

Did you know ... ?

A red-and-yellow striped hermit crab leans out of a cone shell.

Recognised content

Featured articles

Featured lists

Good articles

Featured images

Full list of featured images

WikiProjects

Selected picture

On a perforated brown surface with large black-ringed yellow patches stands a shrimp. It is bright red with a few white horizontal bands.
Cscr-featured.svg Credit: Nick Hobgood

Periclimenes imperator (Decapoda: Palaemonidae) is a species of shrimp with a wide distribution across the Indo-Pacific that lives commensally on a number of hosts, including the sea slug Hexabranchus.

Taxa

indicates an extinct taxon.

Topics

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.

Categories

Related portals

Associated Wikimedia

The following Wikimedia Foundation sister projects provide more on this subject:

Wikibooks
Books

Commons
Media

Wikinews 
News

Wikiquote 
Quotations

Wikisource 
Texts

Wikiversity
Learning resources

Wikivoyage 
Travel guides

Wiktionary 
Definitions

Wikidata 
Database

Wikispecies 
Species