Alex Mustard / Sacoglossan sea slug (Costasiella sp.) tiny <5mm along, on algae. Anilao, Batangas marine protected area, Luzon, Philippines. Verde Island Passages, Tropical West Pacific Ocean.

Pascal Kobeh / Lined Thuridilla / Orange-edged sapsucking nudibranch / sea slug (Thuridilla lineolata), Sulu sea, Philippines

Linda Pitkin / Nudibranch (Thuridilla lineolata) Sangeang, off Sumbawa, Indonesia.

Georgette Douwma / Sea slug (Plakobranchus ocellatus) on sand. Raja Ampat, West Papua, Indonesia.

Alex Mustard / Tiny (7mm) herbivorous sap-sucking seaslug (Costasiella kuroshimae) crawling over piece of algae next to its circular egg ribbon. Seraya, Bali, Indonesia. Java Sea

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...

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

Alex Mustard / Sap-sucking slug / Shaun the sheep slug (Costasiella kuroshimae) crawling across algae (Avrainvillea sp.) on the seabed, Bitung, North Sulawesi, Indonesia, Lembeh Strait.

Alex Mustard / Sap-sucking slug / Shaun the sheep slug (Costasiella kuroshimae) crawling across green algae (Avrainvillea sp.) on seabed, Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

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