Two families of hot stellar systems, named {it `ordinary'/} and {it 'bright'/}, are identified in the ($log R_e, mu_e$) plane built with a luminosity--limited sample of ellipticals and bulges of S0s and spirals of the Virgo and Fornax clusters. This finding, based on {it ad hoc/} new observations, is confirmed by a much larger set of literature data for $sim1500$ galaxies. The {it `ordinary'/} family is biparametric: $L_Tpropto I_e,R_e^2$; its members are fainter that $M_Bsimeq-19.3$ and smaller than $ esimeq3$ kpc (whatever $M_B$ is). The {it 'bright'/} family is uniparametric ($mu_e$ depends on $R_e$ alone) and hosts brightest cluster members and QSO parent galaxies. We show that the segregation in the ($log R_e, mu_e$) plane has an important counterpart in the behavior of various physical parameters, which is markedly different for galaxies smaller ({it `ordinary'/} family) and larger ({it 'bright'/} family) than $R_e=3$ kpc.