Shell solid, equivalve, inequilateral. Outline mussel-like with subterminal umbones. Sculpture of many strong radial, occasionally bifurcating, ribs crossed by finer concentric lines giving them a nodulous appearance. Hinge with 2-3 large teeth below the umbo, 4-6 large dysodont teeth behind the ligament. Septum across umbonal cavity. Inner margin crenulate. Periostracum of simple long fine bristles.
externally light green with orange pink spots. Internally, light green and pink tinted.
common size :
in Red Sea up to 11.5 mm (Dekker, pers. comm.); the Mediterranean specimen smaller (the biggest 9.5 x 5 mm).
Similar to Brachidontes pharaonis externally but internally with a septum beneath umbones. Differs from the Indo-Pacific Septifer bilocularis in size - S. bilocularis can attain a length up to 50 mm - and in color - S. bilocularis is typically red, blue or green.
BIOLOGY / ECOLOGY
Suspension feeders, epifaunal, actively mobile. The biology, ecology and use as a bioindicator of its congeneric S. bilocularis has been studied by Ompi and Lumingas (1997) and Kavun (1996).
attached by byssus to rocks and debris (corals, shells), lower shore and shallow water. The Mediterranean specimen was found attached to a Spondylus spinosus shell, at a depth of 40 m.