What is a Nudibranch?
A clear introduction to nudibranchs, what makes them different from other sea slugs, and why they are such popular macro subjects.
Read the guideMacroDivers focuses mainly on nudibranchs, but we also include related sea slugs that divers and macro photographers commonly encounter on the same dives.
These guides explain how nudibranchs and sea slugs are built, how they are classified, how to identify them, and how the MacroDivers species database uses practical field features such as body type, rhinophores, gills, colour, food source and location.
This section is designed for divers, underwater photographers and anyone learning to recognise the small, colourful and often overlooked animals found on reefs, rubble slopes, muck sites and seagrass beds.
Start Here
Start Here
New to nudibranchs and sea slugs? Start with the basics: what they are, how they are grouped, and why scientific names matter.
Orders & Types of Sea Slugs
A practical guide to the sea slug groups and categories used in the MacroDivers species database.
View category guideScientific Names
A simple explanation of scientific names, why they change, and how they help avoid confusion in identification.
Understand namesNudibranch Anatomy
Learn the key external features used in identification, including rhinophores, oral tentacles, mantle, foot, cerata and external gills.
View anatomy guideIdentification Basics
Identification Basics
These guides explain the practical features we use when identifying sea slugs and organising records in the MacroDivers database.
How to Identify Nudibranchs & Sea Slugs
Practical tips for identifying nudibranchs and related sea slugs using body shape, colour, pattern, anatomy, food source, habitat and location.
Learn identificationNudibranch & Sea Slug Body Types
Understand the practical body-shape categories used in the MacroDivers database, including oval, elongate, robust, with appendages, with visible shell and other.
Explore body typesRhinophores
A visual guide to rhinophore shapes, from ringed and smooth to rolled, branched and pocket-like forms.
Study rhinophoresNudibranch Gills
Understand external gill plumes, cerata, hidden gills and how these breathing structures help with identification.
Explore gill typesKey Features & Life
Key Features & Life
Once you understand the basic body plan, these pages look more closely at the structures, behaviours and life stages that help explain what you see underwater.
Food Guide
Learn how food sources help divers find and identify nudibranchs and related sea slugs more effectively.
Find food sourcesBehaviour
Feeding, movement, defence, mating and other behaviours divers can observe underwater.
Learn behaviourLife Cycle
Egg ribbons, larval stages, growth and the remarkable life cycle of nudibranchs.
Explore life cycleFinding & Recording
Finding & Recording
Use these guides to connect what you learn underwater with real dive destinations and the MacroDivers species database.
Hotspots
Where to look for nudibranchs and sea slugs, and why some destinations are especially good for macro life.
Explore hotspotsSpecies Database
Search the MacroDivers species database using practical field clues including body type, colour, rhinophores, gills and location.
Search the database