An enneiamond is a figure made of nine equilateral triangles joined
edge to edge.
A Galvagni figure is a figure that can be tiled by a polyform
in more than one way—a kind of self-compatibility figure.
A Reid figure is a Galvagni figure without holes.

Galvagni Figures

Here are the known minimal Galvagni figures for enneiamonds: