Habitus and skeleton of Grantia compressa from Roscoff, W coast of France (ZMA Por. 04159). a preserved specimens showing leaf-like habitus (scale bar = 1 cm) b SEM image of cross section of the leaf-like wall, showing the cortical brushes of club-shaped diactines and cortical triactines, rows of tubar triactines ending near the atrial region with subatrial triactines, closed off by mixed layer of atrial triactines and tetractines with the apical actines of the tetractines protruding beyond the atrial surface c overview of atrial surface and atrial chambers with protruding apical actines of the atrial tetractines d detail of atrial chamber lacking differentiated spicules.