Great enneagrammic retroprism

The great enneagrammic retroprism, or gisterp, also called the great enneagrammic crossed antiprism, is a prismatic uniform polyhedron. It consists of 18 triangles and 2 great enneagrams. Each vertex joins one great enneagram and three triangles. As the name suggests, it is a crossed antiprism based on a great enneagram, seen as a 9/5-gon rather than 9/4.