1	P2exp-3 with 2 outer spines; genital double-somite barrel-shaped in female	S. humesi
–	P2exp-3 with 3 outer spines; genital double-somite oval-shaped or elongate oval-shaped in female	2
2	Md with 5 elements; undulate or lobate hyaline frill at posterior margin of urosomites strongly pronounced; inner margin of caudal ramus with row of setules; modified seta III (spine) on caudal ramus very strong	S. ivlevi
–	Md with 4 elements; undulate hyaline frill at posterior margin of urosomites weakly pronounced; inner margin of caudal ramus naked; modified seta III (spine) on caudal ramus less strong	S. tenuis