Order Lychniscosida

includes a once diverse and dominant group of fossils from Cretaceous benthic communities, now contains only two families and three genera as Recent members. The group is characterized by formation of a rigid dictyonal framework by fusion of lychniscid hexactins mainly by fusion of rays of adjacent dictyonalia arranged sideby-side — a euretoid pattern of junction. The length of rays which form the sides of dictyonal meshes is strictly limited to one mesh width, usually 150–400µm. The constituent families are differentiated by thickness of structural units (walls, pillars, plates) and organization of dictyonalia — either in ranks or without detectable alignments. Structural units (tubule walls, pillars) are unchannelized, but it is possible to interpret the fine wall tubules of Diapleuridae as schizorhyses.