It sounds like a leafminer, although I couldn't say for sure without having a look at the leaf. Best way to deal with leafminers is to cut off the affected foliage at first sight of damage. Be careful what you do with the discarded leaf, throw it in the bin and NOT on the compost heap or near other uncontaminated plants. You could use an insecticide if you are that way inclined, but should be able to beat them by pulling off the leaves.