Caterpillars have the 6 legs of other insects, plus up to ten 'prolegs' that distinguish them as the grubs of moths or butterflies. The 6 true legs are jointed, with a little claw on the end of each. Prologs are cylindrical, not jointed, with a tiny hook that makes them good for walking or clinging. The 6 true legs on the thorax remain throughout pupation, and these become the legs of the adult butterfly or moth. The prolegs disappear.
Some species have fewer than six.
There is an oval opening called a 'spiracle' on each side of each segment. As the caterpillar moves, air is pumped into the trachea, causing oxygen to be taken in and carbon dioxide to be pushed out. Caterpillars do not actually breathe as we do, but air is exhanged by the compression and extension of each segment. It's not really known if caterpillars can hear. They make no noise other than chewing.