ancient murrelet; murrelet
A small seabird, Synthliboramphus antiquus. In everyday Japanese, the katakana name ウミスズメ is standard.
The ancient murrelet breeds along the coasts of the North Pacific.
I spotted an ancient murrelet while birdwatching.
roundbelly cowfish
A boxfish, Lactoria diaphana. This sense is less common and may be encountered mainly in marine biology contexts.
I saw a fish called roundbelly cowfish at the aquarium.
least auklet
Katakana spelling is common for this bird name; usually written in kana.
Kanji form is rare and may not be widely recognized; the source does not list it as a priority form.
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.