  The existence of closed loops of degeneracies in crystals has been intimately
connected to associated crystal symmetries, raising the question: what is the
minimum symmetry required for topological character, and can one find an
example? Triclinic CaAs$_3$, in space group $P{\bar 1}$ with only a center of
inversion, has been found to display, without need for tuning, a nodal loop of
accidental degeneracies with topological character, centered on one face of the
Brillouin zone that is otherwise fully gapped. The small loop is very flat in
energy, yet is cut four times by the Fermi energy, a condition that results in
an intricate repeated touching of inversion related pairs of Fermi surfaces at
Weyl points. Spin-orbit coupling lifts the fourfold degeneracy along the loop,
leaving trivial Kramers pairs. With its single nodal loop that emerges without
protection from any point group symmetry, CaAs$_3$ represents the primal
"hydrogen atom" of nodal loop systems.
