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Arthropods
Phylum
Arthropoda
Any of numerous invertebrate animals of the phylum Arthropoda, including the insects, crustaceans, arachnids, and myriapods, that are characterized by a chitinous exoskeleton and a segmented body to which jointed appendages are articulated in pairs.
[American Heritage Dictionary]
An arthropods most obvious characteristic is the tough encasement of armor, or
exoskeleton. This armor is made principally of a substance called chitin, secreted by the underlying epidermal cells.
The exoskeleton has joints, regions where chitin is thin and flexible, permitting movements.
Such joints are particularly obvious on the legs, and give the phylum its name, Arthropoda, which
means "jointed foot" in Greek. Movement is achieved by muscles attached inside the skeleton,
rather then on the outside as in human beings.
[
National Audubon Society Field Guide of North American Seashore Creatures.
]
Classes of Phylum Arthropods
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