Bibliographia Nudibranchia, Gary McDonald
- A comprehensive bibliography of the literature about nudibranchs, exluding textbooks and local field guides.
- http://repositories.cdlib.org/cgi/viewcontent.cgi?article=1001&context=ims

Nudi Pixel
- Online nudibranch identification using a collection of photographs taken from various location worldwide.
- http://www.nudipixel.net/

Scottish Nudibranchs
- Deals almost exclusively with this part of the world.
- http://www.scottishnudibranchs.co.uk/scotnud1.html

Nudibranch Roundup
- Photographs and introduction by Phillip Slosberg.
- http://www.cybereef.com/seaslugs/Pages/roundup.htm

Sulawesi Sea Slugs
- Images and information of species seen near North Sulawesi, Indonesia in June 2001.
- http://www.bunaken.pwp.blueyonder.co.uk/sss-sea-slugs.htm

Singapore Nudibranchs
- Data available on sites and dates of collection of nudibranchs.
- http://rmbr.nus.edu.sg/nudibranch/main.html

Nudibranchs of Norway
- Knowledge of Norwegian suggested for this site.
- http://www.marinbi.com/nudibranchia/index.htm

Nudibranchs of Costa Rica: The Slugophile
- Photographs, an interactive sightings form for divers from around the world, some general information, and a touch of anatomy. Concentrated mostly on opisthobranchs of Costa Rica.
- http://www.slugophile.org

Australian Nudibranchs
- Description, classification and photographs of nudibranchs, as well as the Australasian Nudibranch News, an online newsletter dedicated to nudibranchs of the Australia/Asia region. Part of a larger site devoted to Australian scuba diving.
- http://www.diveoz.com.au/nudibranchs/nudibranch.asp?info=main_page

Opisthobranchs of Kii Penninsula
- The page is in Japanese.
- http://www.sea-slug.com/species/index.html

Nudibranchs of the Poor Knight Islands
- Images of some New Zealand nudibranchs.
- http://www.divenz.co.nz/nudibranchs.htm

Fabio's Nudibranch Gallery
- A small gallery of nudibranch pictures that is part of Fabio's Sealife Picture Gallery.
- http://www.wgn.net/~fabio/gallery/nudibranch.htm

Nudibranchs and Marine Flatworm of the World
- Photos of nudibranchs from the Mediterranean, Indian Ocean, and the Red Sea. Unfortunately (from a certain perspective), there is more information about flatworms on this site than about nudibranchs.
- http://www.rzuser.uni-heidelberg.de/~bu6/index.html

Em nau! Nudibranchs
- A rundown of some of the nudibranchs found in Papua New Guinea. Part of a larger site dedicated to this corner of the world.
- http://www.uga.edu/cuda/nudis.html

Opisthobranchs of Ross Island & McMurdo Sound, Antarctica
- Electronic field guide of Antarctic opisthobranchs. Part of overall marine field guide to Antarctica. Web site by Peter Brueggeman, SIO librarian. Photos by Norbert Wu, P. Brueggeman, and Kathleen Conlan.
- http://scilib.ucsd.edu/sio/nsf/fguide/branchs.html

Sea Slug Forum
- You can ask questions and post information on nudibranchs and other related sea slugs such as bubble-shells, sea hares and side-gilled slugs.
- http://www.seaslugforum.net/

The Okinawa Slug Site
- A site featuring Okinawan Opisthobranch Molluscs, nudibranchs and other related sea slugs such as bubble-shells, sea hares and side-gilled slugs.
- http://rfbolland.com/okislugs/index.html

The Slug Site
- Devoted to the study of opisthobranch molluscs.
- http://slugsite.tierranet.com/

Jeff's Nudibranch Page
- Devoted primarily to the nudibranchs of the Philippines, but also contains information and photographs about crinoids (Echinodermata) and reef organisms in general.
- http://divegallery.com/

Opisthobranchia Around Hachijo Island
- Photographs of nudibranchs from the Izu-Islands group of Japan.
- http://www.mars.dti.ne.jp/~furuse/watching/SLUG/SLUG.html

Sharif's Malaysian Slugsite
- Contains photographs of Malaysian nudibranchs and links to other nudibranch sites.
- http://www.eperak.com/slugsite/

Mediterranean Slug Site
- A plethora of photos and information about Opisthobranchs from the Mediterranean Sea. Also includes nudibranchs from parts of the world other than the Mediterranean.
- http://www.medslugs.de/