In 1974, Kaplinskaja classified all simplicial straight hyperbolic Coxeter prisms. In this paper, we determine precisely which of these prisms are properly quasi-arithmetic or arithmetic. We also present some observations regarding commensurability classes and systoles of the associated orbifolds. Finally, we show that there is a cocompact properly quasi-arithmetic reflection group in H 3 preserving an isotropic quadratic form. This phenomenon was previously known due to Vinberg only in dimension 2.