noun
moon jellyfish; Aurelia aurita
Refers specifically to the moon jellyfish (Aurelia aurita), a common translucent jellyfish found in coastal waters worldwide.
水族館で水水母がふわふわと泳いでいた。
The moon jellyfish were floating gently in the aquarium.
海月 is the general term for jellyfish, while 水水母 specifically refers to the moon jellyfish (Aurelia aurita).
The kanji 水水母 literally means 'water water mother', likely a direct translation or calque of the scientific name or a descriptive term for the jellyfish's appearance. The reading みずくらげ combines 水 (みず, water) with くらげ (jellyfish).