noun
sea slug; nudibranch
Refers to various marine gastropods, especially nudibranchs. The term is used broadly for colorful sea slugs.
See also: 海鼠
ウミウシは色鮮やかな種類が多い。
Many sea slug species are brightly colored.
ダイビング中に珍
I found a rare sea slug while diving.
海鼠 is sea cucumber, a different marine animal; ウミウシ is a sea slug, often colorful and shell-less.
Compound of 海 (umi, 'sea') and 牛 (ushi, 'cow, ox'), literally 'sea cow'. The name likely comes from the slug's cow-like tentacles (rhinophores) resembling horns.