an edible river snail
蜷 centers on a specific edible river snail. The meaning is narrow and concrete, referring to the creature itself.
蜷 combines 虫 (insect/creature) with 卷, which likely contributes the sound. The character specifically denotes a type of snail.
The left side 虫 signals a small creature, and the right side 卷 looks like a coiled shape. Picture a snail curled up inside its shell: 蜷 is that edible river snail.
For ケン, imagine Ken the snail collector picking up a coiled river snail: Ken -> ケン, and the snail curls up in his hand.