Choose an embedding of *X* in projective space.  Since your curves are all in the same homology class, they all have the same degree: this is simply the intersection number of the ample class with the homology class of the curves.  Generic projection to a plane tells you that the curves you are interested in are partial normalizations of plane curves with bounded degree. Since the arithmetic genus decreases under (partial) normalizations, and since the arithmetic genus of a plane curve of bounded degree is bounded, you conclude that the arithmetic genera of your curves are bounded.