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).
*Molecular data has recently separated S. costatum into several species. These distinctions cannot be made without detailed examination of their morphology (Sarno et al. 2005, and Zingone et al. 2005, all cited in Kraberg et al. 2010).