Marine species guide
Nudibranch
Nudibranchs are shell-less sea slugs prized by macro photographers. Patterns are vivid—but many species look alike until you check rhinophores, gills and location.
Identification features
Rhinophores (sensory tentacles) on the head and a plume of gills or cerata on the back are classic marks. Colours advertise chemical defences gathered from prey such as sponges and hydroids.
- Rhinophores and gill plume or cerata
- Bright warning colours
- Usually on specific prey substrates
- Macro-sized
Habitat and behaviour
Size is often 1–10 cm. Use a dive slate or photo to note background organism (sponge colour often matches the slug).
Where and when to see them
Lookalikes include flatworms (no rhinophores) and small fish. Slow searching on walls and overhangs pays off.
Dive tips
Lookalikes include flatworms (no rhinophores) and small fish. Slow searching on walls and overhangs pays off.
Frequently asked questions
How do I confirm the ID?
Combine visible traits with location and depth, then compare photos in Scuba Steve’s fish identification app and regional guides.
Should I touch it?
No. Maintain neutral buoyancy and a respectful distance for safety and animal welfare.
Where can I learn more?
See related dive-site guides on Scuba Steve and ask local operators about recent conditions.