Arthropods

Definition

Invertebrate animals constituting the phylum Arthropoda, characterized by a segmented body plan, paired jointed appendages, and a rigid exoskeleton of chitin (often mineralized with calcium carbonate) that is periodically shed through ecdysis (moulting) to permit growth. The phylum encompasses insects, arachnids, crustaceans, and myriapods, representing the most species-rich and ecologically diverse animal lineage.

Etymology

From Greek arthron (joint) + podos (foot), referring to the jointed appendages diagnostic of the group.

Example

Beetles, spiders, and crabs are all arthropods, sharing the fundamental body plan of segmented regions with jointed limbs and a non-living external skeleton.

Synonyms

• Arthropoda (phylum name, formal)

Related Terms

• Exoskeleton
• Ecdysis
• Chitin
• metamerism
• Chelicerata
• Mandibulata
• hexapods
• crustaceans
• myriapods
• invertebrate

Usage Notes

Used as the common plural for members of phylum Arthropoda; singular 'arthropod' applies to any individual member regardless of subgroup. The term is rank-neutral above the species level and contrasts with 'vertebrates' and other invertebrate phyla such as Mollusca or Annelida. In entomology and arachnology, 'arthropod' often serves as the broader taxonomic umbrella when discussing shared anatomy, physiology, or ecological roles across insects and arachnids.