Pentagonal double antitegmoid

The pentagonal double antitegmoid or pentaantitegmatoswirlic hectochoron is a convex isochoric polychoron and member of the double antitegmoid family with 100 order-5 truncated bi-apiculated tetrahedra as cells. It can be obtained as the dual of the uniform grand antiprism. It is the first in an infinite family of isochoric pentagonal antitegmatic swirlchora.

It can be constructed by raising tall pyramids on 20 of the cells of the hecatonicosachoron corresponding to the vertices of an decagonal duotegum such that adjacent cells merge into order-5 truncated bi-apiculated tetrahedra.

Being the dual of the grand antiprism, this shape is sometimes called the grand antitegum, in analogy to how antitegums are the duals of antiprisms. Despite this name, this shape is neither a stellation nor an antitegum in any common sense of the word.

The cells of this polychoron can be constructed by augmenting tall pyramids onto two of the faces of a regular dodecahedron. As such they each have 4 identical geometrically regular pentagonal faces, with 2 isosceles trapezoids and 4 kites as well.

The ratio between the longest and shortest edges is $$1:\frac{3+\sqrt5}{2}\approx 1:2.61803$$.

Variations
The pentagonal double antitegmoid is part of a continuum of more general isochoric variations with full symmetry. It has one degree of variation. These polychora have mirror-symmetric pentagons instead of fully regular pentagons.