Arenas del Mar is near Manuel Antonio, right? So it has to be a Common Basilisk (only occuring in the Pacific region and the Brown Basilisk is it's Caribbean counterpart).
There are quite a few species of reptile and bird in Costa Rica and western Panama that are very much alike and can be regarded as Caribbean and Pacific counterparts of each other. Passerini's and Cherrie's tanagers are a good example (I don't know of you saw these).
