The membrane in the figure is the plasma membrane, with the
extracellular side being at the top right. The 'toadstool', which has
been described in the Entamoeba literature as a 'bullet' or a 'T-bar'
among other names, is presumed to be part of the virus as it is not a
normal component of the plasma membrane (unless the viruses are
considered to be!). They have been reported occasionally through the
years mostly in the cytoplasm where they can form rosettes. Very similar
pictures, although not quite as sharp, were published in 1976 (Mattern
et al, In B. Sepulveda and L. S. Diamond (Eds.), Proceedings of the
International Conference on Amebiasis, Mexico City pp. 346-357) but may
not be easily accessible in many libraries...
I'm curious to hear what your colleague thinks...