Nudibranchs are often casually called "sea slugs", a non-scientific term. This has led some people to assume that every sea slug must be a nudibranch. Nudibranchs are very numerous in terms of species, and are often very attractive and noticeable, but there are a wide variety of other kinds of sea slugs, and these belong to several taxonomic groups that are not very closely related to nudibranchs. A fair number of these other sea slugs are colorful, and can be confused with nudibranchs.
