[en] We study the spectrum of an integrable antiferromagnetic Hamiltonian of the gl(M vertical stroke N) spin chain of alternating fundamental and dual representations. After extensive numerical analysis, we identify the vacuum and low lying excitations and with this knowledge perform the continuum limit, while keeping a finite gap. All antiferromagnetic gl(n+N vertical stroke N) spin chains with n>0 and N≠0 are shown to possess in the continuum limit 2n-2 multiplets of massive particles which scatter with gl(n) Gross-Neveu like S-matrices, namely their eigenvalues do not depend on N. We argue that the continuum theory is the gl(M vertical stroke N) Gross-Neveu model, that is the massive deformation of the gl(M vertical stroke N)₁ Wess-Zumino-Witten model. As we can see ion the example of gl(2m vertical stroke 1) spin chains, the full particle spectrum is much richer. Our analysis suggests that for a complete characterization of the latter it is not enough to restrict to large volume calculations, as we do in this work. (orig.)