Copepod - Macrycyclops
In order to further clarify (or further confuse) the 'Where are you legs?' question for Crustacea, it may be helpful to look a the example of the Copepod Macrocylops.
As one progresses head downwards, one can observe that as for many Crustacea (such as the lobster) of the two pairs of antennae one is very pronounced and the other is not. Recall that even in the barnacle one antenna pair is vestigial while the other is not (albeit bearing very very little resemblance to the lobster's).
An excellent example of how the 'Where are your legs?' question is complex, we see that in Macrocyclops the mandibles below the antennae are in fact the 'legs' of the third body segment (or the fourth body segment) and they are adorned with feathery 'setae' which aid in filter feeding - which is how this Copepod feeds from the water in which it lives.
Another pair of legs goes by the wayside to form the labrum, which is in fact two completely fused appendages ('legs') from another body segment and serves to form a stiff, yet rapidly moving, 'upper' lip which covers the 'mouth' of the Macrocyclops. Next in Macrocyclops are its 'maxilla' or 'maxillipeds' which are a continuation of the feeding appendages aiding in filter feeding.
Only when we get down the the 'thoracic appendages' do we begin to get a feeling that we are seeing any legs at all for Macrocyclops.