Costigulella primennilus spec. nov. is the first representative of Costigulella reported from Cameroon. It is probably the smallest species of the family Streptaxidae known world-wide. Arguments are provided to consider Costigulella an independent radiation and genus, rather than a subgenus of Gulella. The mode of development of apertural barriers in juvenile shells in Costigulella and in other Streptaxidae is discussed.