I believe spiral cleavage is a characteristic cleavage of protostomes in which the 8 or 16-cell embryo does not line up or exhibit any symmetry.
Radial cleavage, just think of a circle because it has a radius, the cleaving is symmetrical and the 8 or 16-cell embryos exhibit this nature. Think of the alignments as a cubic lattice.
-Spiral Cleavage: occurs such that the resulting daughter cells are not located exactly on top of one another; instead, they are located at a slight angle. Spiral cleavage is a characteristic of Protostomes, and results in determinant cells (Cell that have a determined embryological fate early on during the development of the embryo). In other words, determinant cells are programmed to become a specific type of cell, early on during the process.
-Radial Cleavage: occurs such that the resulting daughter cells are located exactly on top of one another. Radial cleavage is a characteristic of Deutrostomes, and results in indeterminant cells (Cells that can individually give rise to a complete embryo, and they don't have a determined embryological fate early on during the development of the embryo). In other words, you can take a single cell from a developing embryo, and given the right condition, that single cell can give rise to a whole embryo (If you've taken embryology classes you've definitely heard of experiments like this done with frog embryo).