earthworm
蚓 centers on the earthworm, a creature that moves through soil. The meaning is narrow and concrete, with no major abstract extensions.
蚓 combines the insect radical 虫 with 引, which likely contributes the sound and suggests the worm's pulling or stretching motion through the earth.
The insect radical 虫 on the left and 引 (pull) on the right suggest a worm that pulls itself through the dirt: an earthworm.
For ズ, imagine a zoo where earthworms are the main attraction, wriggling and pulling through the soil: zoo -> ズ.
Iberian worm lizard (Blanus cinereus); European worm lizard
Marphysa sanguinea (species of eunicid worm)
Epimenia verrucosa (mollusc)
eunicid (any worm of family Eunicidae)
earthworm
worm lizard; amphisbaenian
flat-headed goby (Luciogobius guttatus)
cry of earthworms (heard on autumn nights and rainy days)