noun
ancient murrelet; murrelet
A small seabird, Synthliboramphus antiquus. In everyday Japanese, the katakana name ウミスズメ is standard.
ウミスズメは北太平洋の沿岸で繁殖する。
The ancient murrelet breeds along the coasts of the North Pacific.
バードウォッチングでウミスズメを見つけた。
I spotted an ancient murrelet while birdwatching.
noun
roundbelly cowfish
A boxfish, Lactoria diaphana. This sense is less common and may be encountered mainly in marine biology contexts.
水族館でウミスズメという魚を見た。
I saw a fish called roundbelly cowfish at the aquarium.
The name ウミスズメ literally means 'sea sparrow', likely from the bird's small size and marine habitat. The fish sense is an extension of the same name.