We present a scaling theory to describe self-assembled multicompartment structures formed by ABC 3-miktoarm star colopymers in a dilute solution in selective solvent. Depending on the degrees of polymerization of solvophilic (A) and solvophobic (B, Q arms and on the ratio between interfacial tensions at the interface between solvent and both collapsed solvophobic blocks, we delinate regions of stability of aggregates of different morphologies. In particular, we demonstrate that copolymers with longer solvophilic (A) block form aggregatively stable starlike micelles with phase-separated cores. Depending on the ratio of interfacial tensions at the interfaces of collapsed B and C blocks with solvent and that at the BC interface, the core of the starlike micelle separates either in 2 (B, C) or in 3 (B, C, B) domains. In the case of relatively short solvophilic blocks we predict formation of cylindrical crew-cut micelles with microphase segregated (alternating in the longitudinal direction) core.