  We construct simple twistor-like actions describing superparticles
propagating on a coset superspace OSp(1|4)/SO(1,3) (containing the D=4
anti-de-Sitter space as a bosonic subspace), on a supergroup manifold OSp(1|4)
and, generically, on OSp(1|2n). Making two different contractions of the
superparticle model on the OSp(1|4) supermanifold we get massless
superparticles in Minkowski superspace without and with tensorial central
charges. Using a suitable parametrization of OSp(1|2n) we obtain even
Sp(2n)-valued Cartan forms which are quadratic in Grassmann coordinates of
OSp(1|2n). This result may simplify the structure of brane actions in super-AdS
backgrounds. For instance, the twistor-like actions constructed with the use of
the even OSp(1|2n) Cartan forms as supervielbeins are quadratic in fermionic
variables. We also show that the free bosonic twistor particle action describes
massless particles propagating in arbitrary space-times with a conformally flat
metric, in particular, in Minkowski space and AdS space. Applications of these
results to the theory of higher spin fields and to superbranes in AdS
superbackgrounds are mentioned.
