Truncated order-8 octagonal tiling

The dual of the tiling represents the fundamental domains of (*884) orbifold symmetry. From [(8,8,4)] (*884) symmetry, there are 15 small index subgroup (11 unique) by mirror removal and alternation operators. Mirrors can be removed if its branch orders are all even, and cuts neighboring branch orders in half. Removing two mirrors leaves a half-order gyration point where the removed mirrors met. In these images fundamental domains are alternately colored black and white, and mirrors exist on the boundaries between colors. The symmetry can be doubled to 882 symmetry by adding a bisecting mirror across the fundamental domains. The subgroup index-8 group, [(1⁺,8,1⁺,8,1⁺,4)] (442442) is the commutator subgroup of [(8,8,4)].

Small index subgroups of [(8,8,4)] (*884)

Fundamental domains
Subgroup index	1	2			4
Coxeter	[(8,8,4)]	[(1+,8,8,4)]	[(8,8,1+,4)]	[(8,1+,8,4)]	[(1+,8,8,1+,4)]	[(8+,8+,4)]
orbifold	*884	*8482		*4444	2*4444	442×
Coxeter		[(8,8+,4)]	[(8+,8,4)]	[(8,8,4+)]	[(8,1+,8,1+,4)]	[(1+,8,1+,8,4)]
Orbifold		8*42		4*44	4*4242
Direct subgroups
Subgroup index	2	4			8
Coxeter	[(8,8,4)]+	[(1+,8,8+,4)]	[(8+,8,1+,4)]	[(8,1+,8,4+)]	[(1+,8,1+,8,1+,4)] = [(8+,8+,4+)]
Orbifold	844	8482		4444	442442