  The geometry and intrinsic ellipticity distribution of ultra diffuse galaxies
(UDGs) is determined from the line-of-sight distribution of axial ratios q of a
large sample of UDGs, detected by Koda et al. (2015) in the Coma cluster. With
high significance the data rules out an oblate, disk-like geometry,
characterised by major axi a=b>c. The data is however in good agreement with
prolate shapes, corresponding to a=b<c. This indicates that UDGs are not
thickened, rotating, axisymmetric disks, puffed up by violent processes.
Instead they are anisotropic elongated cigar- or bar-like structures, similar
to the prolate dwarf spheroidal galaxy population of the Local Group. The
intrinsic distribution of axial ratios of the Coma UDGs is flat in the range of
0.4 <= a/c <= 0.9 which will provide important constraints for theoretical
models of their origin. Formation scenarios that could explain the extended
prolate nature of UDGs are discussed.
