If you mean midas blennies they are easy to feed and mine eats everthing. Scooter blennies are the hard ones.
As for them looking similar to gobies, generally blennies get larger and they swim differently. And different types of blennies or gobies will have different swimming habits. For example, midas blennies will perch on a rock or in a cave with just their head sticking out, but when they see something interesting like food they will come out to check it out. Scooter blennies, from what I've seen, tend to hop around on the sand looking for pods.
CageUK, was it a jawfish?