Foot shape. A–C Orientation of the foot (grey areas and arrows) A directed dorsally (S. tremula) B coplanar with the longitudinal axis (S. grimpei) C directed ventrally (S. longipes) D–I Shape and size of the foot (grey areas) D minute, shorter than the toes (S. atlantica) E triangular, medium (S. triophthalma) F conical, medium (S. tremula) G slender, long (S. longipes) H broad, long (S. johanseni) I massive, cylindrical (S. pachypoda). Drawings modified from: D Zelinka (1907) H Harring (1921) I Kutikova and Vassiljeva (1982). Scale bar: 50 µm.