1.- Jointed appendages; ancestrally, one pair to each segment, but number often reduced; appendages often modified for
2.- Living in marine, freshwater, and terrestrial habitats; many capable of flight.
3.- Free-living and parasitic taxa.
4.- Bilateral symmetry; segmented body divided into functional groups called tagmata: head and trunk; head, thorax, and abdomen; or cephalothorax and abdomen; definite head.
5.- Triploblastic body.
6.- Reduced coelom in adult; most of body cavity consisting of hemocoel (sinuses, or spaces, in the tissues) filled with blood.
7.- Cuticular exoskeleton; containing protein, lipid, chitin, and often calcium carbonate secreted by underlying epidermis and shed (molted) at intervals; although chitin occurs in a few groups other than arthropods, its use better developed in arthropods.
8.- Complete digestive system; mouthparts modified from ancestral appendages and adapted for different methods
of feeding; alimentary canal shows great specialization by having, in various arthropods, chitinous teeth, compartments, and gastric ossicles.
9.- Complex muscular system, with exoskeleton for attachment, striated muscles for rapid actions, smooth muscles for visceral organs; no cilia.
10.- Nervous system similar to that of annelids, with dorsal brain connected by a ring around the gullet to a double nerve chain of ventral ganglia; fusion of ganglia in some species.
11.- Well-developed sensory organs; behavioral patterns much more complex than those of most invertebrates, with wider occurrence of social organization.
12.- Parthenogenesis in some taxa.
13.- Sexes usually separate, with paired reproductive organs and ducts; usually internal fertilization; oviparous,
ovoviviparous, or viviparous; often with metamorphosis.
14.- Paired excretory glands called coxal, antennal, or maxillary glands present in some; others with excretory organs called Malpighian tubules.
15.- Respiration by body surface, gills, tracheae (air tubes), or book lungs.
16.- Open circulatory system, with dorsal contractile heart, arteries, and hemocoel (blood sinuses).
Integrated principles of zoology / Cleveland P. Hickman, Jr. ... [et al.]. – 14th ed. p. cm.