Abstract (WSP)
It is shown that an explicit incorporation of twistor variables into the lagrangian of a massless relativistic particle together with the local supersymmetrization of its proper time leads to a lagrangian which is invariant under the space-time global supersymmetry. The equivalence of the Siegel symmetry and the local proper-time supersymmetry with a complexified Grassmann parameter is established. The Siegel algebra is formed by an irreducible set of covariant constraints and is closed off-shell.