A new off-lattice Brownian dynamics simulation potential for wormlike micelles in the framework of equilibrium polymerization is proposed. The system reproduces the complete experimentally observed dependence of mean chain length < L > with concentration phi for uncharged species: a very slow dependence at very low phi, a < L >proportional to Phi(0.5) in the dilute and semidilute regime, and an enormous growth with concentration at high phi. Besides, it is shown that at high phi the longest chains are swollen by the smallest, suggesting a Russian dolls picture of the system.