A class of Fock representations of non-central extensions of the
super-diffeomorphism algebra in (N+1|M) dimensions is constructed, by
superization of the paper [physics/9705040]. The representations act on
trajectories in (N|M)-dimensional superspace, the extra dimension being the
parameter along the trajectory. The restrictions to various subalgebras are
considered. In particular, the centrally extended superconformal algebra is
obtained by restriction to the contact superalgebra K(1|1). This shows that one
of the basic assumptions in superstring theory (the distinguished nature of the
superconformal algebra) is incorrect.