Shells
Shells are present during the larval stage but are shed; adults are shell-less.
Species Guide
What to know about nudibranches
A clean field guide focused on habitat, identification, behavior, and conservation context without burying the useful parts.
Nudibranchs are a group of soft-bodied marine gastropod molluscs in the order Nudibranchia that lose their shells after the larval stage. They are noted for often extraordinary colours and striking body forms and have earned colourful common nicknames such as "clown", "marigold", "splendid", "dancer", "dragon" and "sea rabbit". The name 'nudibranch' derives from Latin nudus (naked) and Ancient Greek bránkhia (gills). Although commonly called sea slugs, nudibranchs are one group within the broader assemblage of sea slugs; several other unrelated sea slug groups can look similar and are sometimes confused with nudibranchs.
Identification
How to identify nudibranches
The visual markers divers can use underwater, plus the species most likely to cause confusion.
Key identification markers
Body type
Soft-bodied marine gastropod molluscs.
Colour and form
Often display extraordinary colours and striking body forms.
Taxonomy
Belong to the order Nudibranchia.
Species count
Approximately 3,000 described species.
Common lookalikes
Sacoglossa
A group of photosynthetic sea slugs that are not closely related to nudibranchs but are often confused with them.
Aglajidae
A family of colourful sea slugs that can resemble nudibranchs and are sometimes mistaken for them.
Other sea slugs
Various other taxonomic groups of sea slugs exist that are not closely related to nudibranchs but may look similar.
Population
Estimated numbers and what we actually know
Published estimates when credible, or an explicit note when no reliable global count exists.
About 3,000 species are known.
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Responsible Encounters
How to dive with nudibranches
Conservation-minded guidance for divers who want the encounter without adding pressure.
Give nudibranch space, avoid blocking the animal's path, and follow local site and operator rules for wildlife interactions with molluscs.
Field Notes
Interesting things worth knowing
Useful species context that makes the encounter more meaningful once you are underwater.
Field notes
Nicknames
Nudibranchs have colourful nicknames such as 'clown', 'marigold', 'splendid', 'dancer', 'dragon' and 'sea rabbit'.
Name origin
The name 'nudibranch' literally means 'naked gills', from Latin and Ancient Greek roots.
FAQ
Frequently asked questions
Clear planning and conservation answers written for search visibility and AI retrieval.
Research Sources
Nudibranch information sources
Primary and credible references behind the field-guide and conservation claims on this page.
Sources 2Last Updated
Nudibranch · Encyclopedia · Wikipedia
Primary wildlife guide source.
Nudibranch · Encyclopedia · Britannica
Supporting wildlife source.
Related Species
More in Molluscs
Related species guides in the same encounter family.
