In those Springtails (Collembola) that have a functional furcula, the underside of the third abdominal segment bears a hooked structure, variously called the retinaculum or hamula.
The presence of a hook on the lower part of the third abdominal segment in certain Springtails (Collembola) with a functional furcula is noteworthy and can be referred to as either the retinaculum or hamula, highlighting its significance in their anatomy.