An indication that mesons are organized in shells, originally expressed with masses,
is converted into number of constituents using a mass unit obtained from a mass multiplicity analysis.
Mesonic and nuclear shells are found to be structurally similar,
with the main meson shell progression extending up to shell 8 and correlated with the quark composition,
and no states beyond the 8th shell. Meson states corresponding to the doubly-magic nuclei
are identified up to the 3rd shell, and in this sequence no states are present for shells 4 and above,
as is the case for nuclei. In this context, the quantization of the meson mass unit suggests
that mesons are solid-phase FCC aggregates of spin 1/2 partons of charge 0, +1 and -1,
arranged with anti-ferromagnetic spin coupling in a variety of charge configurations
related to J^(PC) and the quark composition. This hypothesis is confirmed by the sharper
shell pattern obtained with eta states. These results are used to formulate the ingredients
of a shell model for mesons. In the emerging picture the number of parameters is considerably
reduced in comparison with the standard model.
12.40.Yx Hadron mass models and calculations
12.90.+b Miscellaneous theoretical ideas and models of particles