WHAT IS AN ARTHROPOD?

By nearly any measure, the most successful animals on the planet are the arthropods. They have conquered land, sea and air, and make up over three-fourths of all currently known living and fossil organisms, or over one million species in all. Since many arthropod species remain undocumented or undiscovered, especially in tropical rain forests, the true number of living arthropod species is probably in the tens of millions. One recent conservative estimate puts the number of arthropod species in tropical forests at 6 to 9 million species.

THERE ARE A LOT

The arthropods constitute over 90% of the animal kingdom and are classified in the phylum Arthropoda. They are distinguished from other animals by an exoskeleton (a skeleton on the outside of the body). Their bodies are divided into distinct parts having both jointed legs and appendages.

INSECTS

Grasshoppers, butterflies, beetles, ants, etc. 1,000,000 described world species. There are three main body regions: head, thorax, abdomen. They have six legs attached to the thorax (which has 3 segments), adults have one or two pairs of wings attached to the thorax (some have none). They have two antennae and lateral compound eyes.

ARACHNIDS

Spiders, scorpions, ticks, mites, etc. 65,000 described world species. The two main body regions: cephalothorax, abdomen. They have eight legs and no antennae. Mouth parts are chelicerae(modified appendages) which in spiders are fangs.

CRUSTACEANS

Classes include crabs, shrimps, lobsters, barnacles, isopods etc. 44,000 described world species. They have two pairs of antennae and 5 or more pairs of legs. Although they are primarily aquatic, few are terrestrial.

CHILOPODS

Centipedes. 2,800 described world species. They have a well-defined head. They have one pair of legs per segment and one pair of antennae.

DIPLOPODS

Millipedes. 10,000 described world species. They have two pairs of legs per segments, first four. They have one pair of antennae, and a well-defined head which is usually cylindrical.