Give three examples of arthropods. how do you know that they are arthropods?

  Three examples of arthropods are, a crab, a centipede, and a spider.    I know a crab is a arthropod because crabs have an external skeleton. Like armor, it protects the arthropods body.  When arthropods are born the exoskeleton is soft but hardens quickly and it can be shed as the creature grows.  Arthropods are invertebrates; which means that they do not have a backbone.   I also know a centipede is a arthropod because they can have many jointed legs or limbs. Spiders have 8 legs, millipedes can have... Hundreds!   I know a spiders are a arthropod because they have a segmented body. This means that they will have a body made up of more than one part.  Spiders have two segments and flies have three segments.

The mass has escaped into a gas which you can not see so the law stays true.