David Fleetham / Nudibranch (Elysia crispata) on sponge, Bonaire Island, Caribbean.

Alex Mustard / Details of ruffled mantle extensions on the Sacoglossan sea slug (Tridachia crispata) These also contain the chloroplasts of their algae food, that continue to photosynthesise inside the mollusc and p...

MYN / Mac Stone / Lettuce sea slug (Elysia crispata) Florida, USA, September. meetyourneighbours.net project

MYN / Mac Stone / Lettuce sea slug (Elysia crispata) three dorsal views, Florida, USA, . meetyourneighbours.net project

Alex Mustard / Lettuce leaf sea slug / nudibranch (Elysia crispata) crawls over the reef, Seven Mile Beach, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Pete Oxford / Lettuce nudibranch (Elysia crispata) Bonaire, Netherlands Antilles, Caribbean

Christian Ziegler / Lettuce Sea Slug (Elysia crispata), Bastimentos Marine National Park, Bocas del Toro, Panama

Pete Oxford / Lettuce Sea Slug (Elysia crispata), Bonaire, Netherlands Antilles, Caribbean

Juergen Freund / Sap sucking sea slug (Elysia ornata) New Ireland, Papua New Guinea

Juergen Freund / Sacoglossan sea slug / Sap sucker (Elysia sp) a herbivore that feeds, mates and lays eggs on one type of host algae, Batangas, Philippines

Juergen Freund / Nudibranch (Elysia sp.)

Juergen Freund / Chromodoris nudibranch (Chromodoris coi) and Elysia nudibranch (Elysia sp.)

Doug Perrine / Lettuce backed nudibranch {Tridachia crispata}, Dominica, Caribbean

Alex Mustard / Seaslug (Elysia sp.) portrait, Raja Ampat, West Papua, Pacific Ocean.

David Fleetham / Ornate sapsucking slug / Ornate elysia (Elysia ornata) on a reef, Yap, Federated States of Micronesia, Pacific Ocean.

Franco Banfi / Nudibranch (Thuridilla hopei), Punta Campanella Marine Protected Area, Amalfi Coast, Italy, Tyrrhenian Sea, Mediterranean.

Franco Banfi / Nudibranch, (Thuridilla hopei), Ponza island, Italy, Tyrrhenian Sea, Mediterranean

Francisco Marquez / Mexican dancer nudibranch (Elysia diomedea) on white background, Islas Marias Archipelago, Marias Biosphere Reserve, Mexico.

Francisco Marquez / Mexican dancer nudibranch (Elysia diomedea) on white background, Islas Marias Archipelago, Mexico.

Francisco Marquez / Mexican dancer nudibranch (Elysia diomedea) on white background, Islas Marias Archipelago, Marias Biosphere Reserve, Mexico.

Francisco Marquez / Mexican dancer nudibranch (Elysia diomedea) on white background, Islas Marias Archipelago, Marias Biosphere Reserve, Mexico.

Pascal Kobeh / Lettuce seaslug (Elysia crispata). Bahamas.

Alex Mustard / Lettuce leaf sea slug (Elysia crispata) on a coral reef. Jardines de la Reina, Gardens of the Queen National Park, Cuba. Caribbean Sea.

Frederique Olivier / Nudibranch (Chromodoris annae), with a Common reef octopus (Octopus cyanea) camouflaged amongst the coral, Uepi Island, Solomon Islands.

Shane Gross / Cose up of pattern detail on the back of a Lettuce Sea Slug (Elysia crispata) The Bahamas.