Subphylum of arthropods
The phylum Arthropoda is so massive that scientists often group them into four major living subphyla (sometimes referred to as classes in general conversation). Each group is defined by its body segments, number of legs, and types of appendages.
1. Hexapoda (Insects):
The most successful group of animals on Earth. The name "Hexapoda" literally means "six legs."
• Key Traits: 3 body segments (head, thorax, abdomen), 6 legs, and usually 1–2 pairs of wings.
• Examples: Ants, beetles, butterflies, bees, and grasshoppers.
• Unique Fact: They are the only arthropods that have evolved the ability to fly.
2. Arachnida (Arachnids):
This group includes spiders and their relatives. They do not have antennae or wings.
• Key Traits: 2 body segments (cephalothorax and abdomen) and 8 legs.
• Examples: Spiders, scorpions, ticks, and mites.
• Unique Fact: Most arachnids are carnivorous and use "book lungs" or specialized tubes to breathe.
3. Crustacea (Crustaceans):
The "armored" group, most of which live in water.
• Key Traits: Hard shells (often reinforced with calcium), 2 pairs of antennae, and branched appendages (legs that split into two).
• Examples: Crabs, lobsters, shrimp, barnacles, and woodlice (pill bugs).
• Unique Fact: While most are aquatic, the pill bug (roly-poly) is a crustacean that lives on land.
4. Myriapoda (Myriapods):
This group’s name means "many feet." They have long, segmented bodies.
• Key Traits: A single pair of antennae and many pairs of legs.
• Examples: Centipedes and millipedes.
How to tell them apart:
Centipedes have one pair of legs per body segment and are predators; millipedes have two pairs of legs per segment and are scavengers.
[Image comparing a centipede with one pair of legs per segment to a millipede with two pairs]
Comparison Summary:
