Arthropoda (Arthropods)

Abstract

The Arthropoda is a phylum of ecdysozoan animals in which the epidermis produces a segmented, jointed and hardened exoskeleton, which has internal musculature. Each segment primitively bears a pair of jointed limbs. Limbs may be uniramous (one branched) or biramous (two branched). Segments tend to be grouped into body regions or tagmata. Each major group of arthropods is characterised by a particular tagmosis. Arthropods include groups that are wholly marine (the extinct trilobites); marine, terrestrial and freshwater (chelicerates and crustaceans); terrestrial and freshwater (insects) or exclusively terrestrial (myriapods). Arthropods exhibit unparalleled diversity and abundance along with a correspondingly large ecological impact. Recent phylogenomic studies are beginning to resolve arthropod relationships. Two of the largest groups of arthropods – crustaceans and insects – form a single clade, the Pancrustacea. A group containing remipede crustaceans is sister to insects. The Mandibulata (Pancrustacea and Myriapoda) is well supported, and the Oligostraca exhibit a sister‐group relationship to all other pancrustaceans.

Key Concepts:

  • Arthropods are characterised by a segmented, jointed and hardened exoskeleton that has internal musculature.

  • Major groups of arthropods exhibit a characteristic tagmosis.

  • Arthropods include trilobites, chelicerates, crustaceans, insects and myriapods.

  • Many arthropods have compound eyes.

  • Arthropod limbs may be uniramous (one branched) or biramous (two branched).

  • Arthropods include the only invertebrate group to evolve flight.

  • Arthropods are both extremely diverse and highly abundant.

  • The Pancrustacea includes the crustaceans and insects.

  • A group containing remipede crustaceans exhibits a sister‐group relationship to insects.

  • The Mandibulata includes the pancrustaceans and myriapods.

Keywords: ecdysozoa; insects; crustaceans; spiders; trilobites; myriapods

Figure 1.

A cross‐section of a typical arthropod segment showing basic characteristics. All arthropods are built from many such segments, which may be modified in various ways.

Figure 2.

Dorsal (a) and ventral (b) views of Limulus polyphemus, the common horseshoe crab of Atlantic and Gulf coasts of North America. This xiphosuran chelicerate shows many typical arthropod features both externally and internally, (c) comparison of the structure of the arthropod brain, for example, that of L. polyphemus and a crustacean and (d) might suggest that the chelicerae of the former are homologous to the second antennae of the latter, but this is far from clear.

Figure 3.

The cuticle and epidermis of a crustacean.

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How to Cite close
Blackstone, Neil W(Oct 2012) Arthropoda (Arthropods). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001603.pub3]