proleg (abdominal proleg, anal proleg)

proleg noun - fleshy foot-like organs, which serve various larvae in place of, or in addition to, true legs. These are especially prominent in caterpillars. Note that larval insects may have both true legs (of which there are typically six) and a variable number of prolegs. See the diagram at right below for depiction of abdominal (or anterior) and anal prolegs in a caterpillar. The hook-like structures on the prolegs, useful in the identification of families of lepidoptera, are called crochets.

Photos and diagrams showing prolegs: