The order includes 4 families. In fresh-water and solonovatovodny reservoirs types often meet: Thalassiosira lacustris (Grun.) Hasle, Stephanodiscus hantzschii Grun., Cyclotella meneghiniana Kutz., C. Ocellata Pant., Sceletonema costatum (Grev.) Cl. Melosira varians Ag.
Cages single or are connected in threadlike colonies. An armor elongated and cylindrical, it is frequent with numerous inserted rims of various form therefore it is almost always visible sideways. Shutters in an outline round or elliptic, often very convex, it is frequent in the form of the pointed cap with a thorn at top. Structure fall gentle, from the small areola usually invisible in a light microscope.
Refer some childbirth which is characterized by single cages with a low-cylindrical armor and round shutters to family of the aktinoptikhovy. A surface of shutters slightly concave or radial and wavy, divided by edges into 6 or more sectors.
Cages single, attached to a substratum the lower shutter or a jellylike leg, are less often collected in the tape-like colonies which are also attached to a substratum. An armor direct or curved in the longitudinal or cross direction. Shutters linear to the shirokoelliptichesky. Structure of shutters the various: the lower shutter has the slit-like seam located on a longitudinal axis of a shutter, top – without seam, but with a longitudinal axial field; both shutters with the cross edges alternating with cross ranks of an areola.