We show that (massive) D = 10 type IIA supergravity possesses a hidden rigid D 9 ≡ SO(9, 9) symmetry and a hidden local SO(9) × SO(9) symmetry upon dimensional reduction to one (timelike) dimension. We explicitly construct the associated locally supersymmetric Lagrangian in one dimension, and show that its bosonic sector, including the mass term, can be equivalently described by a truncation of an E 10 /K(E 10 ) non-linear σ-model to the level ℓ ≤ 2 sector in a decomposition of E 10 under its D 9 subalgebra. This decomposition is presented up to level ℓ = 10, and the even and odd level sectors are identified tentatively with the Neveu-Schwarz and Ramond sectors, respectively. Further truncation to the level ℓ = 0 sector yields a model related to the reduction of D = 10 type I supergravity. The hyperbolic Kac-Moody algebra DE 10 , associated to the latter, is shown to be a proper subalgebra of E 10 , in accord with the embedding of type I into type IIA supergravity. The corresponding decomposition of DE 10 under D 9 is presented up to level ℓ = 5. † Address after