Results are reported for a molecular dynamics simulation study of a flexible model mesogen composed of seven tangential spheres. We follow the ‘rattling spheres’ method by which bonded atoms are constrained to lie within narrow potential wells. The dynamics of the system is that of a hard sphere fluid with added constraints. The phase diagram of our model system is calculated as a function of density and shows the presence of three fluid phases. These are assigned to be isotropic, nematic and smectic-A phases. Results are reported for the orientational order, radial distribution functions, structure factors and single-particle structural data within these phases. A small but significant change in shape is measured as the nematic phase is entered from the isotropic liquid. This is interpreted in terms of a quenching of allowed conformations parallel to the director.