Cells are short and cylindrical, usually connected in long, straight or slightly undulate chains by a
marginal ring of spines
(strutted processes). The
valve face is convex to flat. Spines interlock midway between adjacent cells, visible as a dotted ring; spine lengths are variable (Horner 2002). There are two chloroplasts per cell and the
nucleus is located centrally (Cupp 1943).
Strutted processes are tubular but semicircular in cross section. One
labiate process is present near the center of the valve inside the ring of
processes (Horner 2002).