noun
sea firefly; seed shrimp
A small bioluminescent crustacean (Vargula hilgendorfii) found in coastal waters of Japan. Often noted for its blue glow.
夜の海でウミホタルが青く光っていた。
The sea fireflies were glowing blue in the sea at night.
Refers to fireflies (insects), while ウミホタル is a marine crustacean, not a true firefly.
Compound of 海 (umi, 'sea') and 蛍 (hotaru, 'firefly'), referring to its marine habitat and bioluminescence.