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The Collaborative International Dictionary

Arthropod \Ar"thro*pod\, n. (Zo["o]l.) One of the Arthropoda. [1913 Webster] ||

Douglas Harper's Etymology Dictionary

1877, from Modern Latin Arthropoda, literally "those with jointed feet," biological classification of the phylum of segmented, legged invertebrates; see Arthropoda.


n. An invertebrate animal of the phylum ''Arthropoda'', characterized by a chitinous exoskeleton and multiple jointed appendages.


n. invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin


An arthropod (from Greek arthro-, joint + podos, foot) is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages (paired appendages). Arthropods form the phylum Arthropoda, which includes the insects, arachnids, myriapods, and crustaceans. 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. 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% of all described living animal species, some of which, unlike most 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 hemocoel, 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. 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 Metazoa 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 as pollinators of crops. Some specific species are known to spread severe disease to humans, livestock, and crops.

Usage examples of "arthropod".

The relief proved short, however, for the ambar turned out to be some sort of arthropod, something like a gigantic cockroach the size of a lobster, half buried under other ambiguous objects and an oily sauce that had been poured over all.

The arthropods, the most populous of the phyla, included creatures like insects, centipedes, millipedes, spiders, and crabs.

Every now and then something crawled out of the slunch: wriggling pale arthropods with masses of tentacles where their heads should have been or those flat, raylike, pincered flying things that she had seen chasing the hawk.

She had examined trees, shrubs, moss, fungi, and arthropods with singular intensity.

Although he had barely a high school education and was self taught in the sciences, Walcott became a leading authority on trilobites and was the first person to establish that trilobites were arthropods, the group that includes modern insects and crustaceans.

The sea swarms with tiny arthropods today that have left no fossil record.

The idea is that just as mammals bided their time for a hundred million years until the dinosaurs cleared off and then seemingly burst forth in profusion all over the planet, so too perhaps the arthropods and other triploblasts waited in semimicroscopic anonymity for the dominant Ediacaran organisms to have their day.

We wandered through a confusion of departments where people sat at large tables doing intent, investigative things with arthropods and palm fronds and boxes of yellowed bones.

This act is called enrolment, a rather common behaviour for arthropods, and it seems to me that this is what Tom has been doing these past weeks.

Vertebrates do it by means of a backbone and internal skeleton, arthropods achieve structural rigidity by means of a tough external skeleton or shell.

Through the mist loomed more many-storied arthropods, gnawing through one another even in death.

Why a cluster of arthropods should escape while a much smaller container of half-centimeter-long wigglers remained behind he could not fathom.

In front of them several dozen small arthropods with metallic green backs were marching along in single file, each using specialized gripping organs to maintain contact with its relative immediately in front.

The single-minded arthropods were not the first example of communal living they had observed among the Xican fauna, but they were by far the most attractive and amusing.

Le-jardin, who was standing outside one of their two huts stacking a half dozen recently collected arthropods held in compact observation and display cases.