Left insect radical - pictograph of a coiled worm or snake. The indexing radical for 蜷. The semantic logic is direct: a curled-up insect is the prototype image of 'to coil, curl up,' which later extended to people huddling in fetal position.
Right 卷 supplies the sound juǎn to quán with a regular shift. It also doubles as semantic: 卷 means 'to roll up,' the precise motion a coiling creature performs. So both sides point at the same image.
