Alex Mustard / Nudibranch (Nembrotha cristata) climbing on a Tunicate (Polycarpa aurata) at night. This species of seaslug feeds on seasquirts. A tiny cyclopoid copepod swimming past. Yillet Yecil, Yillet Islands, M...

Constantinos Petrinos / Chromodorid nudibranch (Chromodoris annae) on Sea Squirt (Polycarpa aurata) Lembeh Strait, North Sulawesi, Indonesia.

SCOTLAND: The Big Picture / Curled octopus (Eledone cirrhosa) amongst a mearl bed, with Lightbulb tunicates (Clavelina lepadiformis) Shetland, Scotland, UK, August.

Georgette Douwma / Kaleidoscopic image of Tunicates including Golden seasquirt (Polycarpa aurata) Lembeh Strait, North Sulawesi, Indonesia.

Alex Mustard / Diver examines a wall covered in large Sea squirts (Ciona intestinalis). Gulen, Bergen, Norway. North Sea, North East Atlantic Ocean.

Sue Daly / Lightbulb sea squirt (Clavelina lepadiformis) Trondheimsfjord, Norway, July.

Sue Daly / Common starfish (Asterias rubens) and sea squirts (Ciona intestinalis), Trondheimsfjord, Norway, July.

Sue Daly / Sea squirt (Ciona intestinalis) Trondheimsfjord, Norway, July.

Constantinos Petrinos / Chromodorid nudibranch (Chromodoris annae) on Sea Squirt (Polycarpa aurata) Lembeh Strait, North Sulawesi, Indonesia.

Alex Mustard / Nudibranchs (Nembrotha chamberlaini) feeding on Tunicates (sea squirt) on a coral reef. Anilao, Batangas, Luzon, Philippines. Verde Island Passages, Tropical West Pacific Ocean..

Georgette Douwma / Durban hinge-beak Prawns (Rhynchocinetes durbanensis) perched on Sea squirt (Polycarpa aurata). Indonesia.

Georgette Douwma / Valentine's puffer (Canthigaster valentini) with Golden sea squirts (Polycarpa aurata) Lembeh, Sulawesi, Indonesia.

Georgette Douwma / Sea squirts: Golden sea squirt (Polycarpa aurata) and Blue club tunicate (Rhopalaea crassa) Lembeh, Sulawesi, Indonesia.

Franco Banfi / Glassy sea squirt (Ascidia paratropa) Vancouver Island, British Columbia, Canada, Pacific Ocean.

Constantinos Petrinos / Chromodorid nudibranch (Chromodoris annae) on Sea Squirt (Polycarpa aurata) Lembeh Strait, North Sulawesi, Indonesia.

Alex Mustard / Slender sapsucking slug (Thuridilla gracilis) on surface of Royal seasquirt (Polycarpa aurata) Aljui Bay, Waigeo Island, Raja Ampat, West Papua, Indonesia. Tropical West Pacific Ocean.

Solvin Zankl / Rich reef landscape with Ox heart ascidian (Polycarpa aurata) and Reef fish, Raja Ampat, West Papua, Indonesia, Pacific Ocean.

Solvin Zankl / Ox heart ascidian (Polycarpa aurata) Raja Ampat, West Papua, Indonesia, Pacific Ocean.

Alex Mustard / A blue light fluorescence photo of light bulb sea squirts (Clavelina lepadiformis). The blue light source excites the fluorescent pigments in the sea squirts which emit light of other colours. The mud...

Franco Banfi / Tunicates (Clavelina lepadiformis) 'Le Formiche' dive-site, Ponza Island, Italy, Tyrrhenian Sea, Mediterranean Sea

Georgette Douwma / Stalked green tunicates (Oxycorynia fascicularis) on coral reef. Rinca, Komodo National Park, Indonesia

Sue Daly / Seasquirt (Oxycorynia fascicularis) Lembeh Straits, Sulawesi, Indonesia

Georgette Douwma / Stalked green ascidian (Oxycorynia facicularis). Rinca, Indonesia.

Florian Graner / Tunicate {Ascidia virginea} Josenfjord, Norway

Alex Mustard / Blenny (Ecsenius sp.) resting on a Royal seasquirt (Polycarpa aurata) on a coral reef, Raja Ampat, West Papua, Ceram Sea, Pacific Ocean.

Franco Banfi / Scuba diver looking at Sea squirts (Ciona intestinalis), Vevang, Norway, Atlantic Ocean. Model released.

Franco Banfi / Sea squirts (Ciona intestinalis) and Sea anemone (Protanthea simplex), Trondheimfjord, Norway, North Atlantic Ocean.

David Fleetham / Close up of the solitary Yellow green tunicate / Sea squirt (Ascidia sydneiensis), Hawaii, Pacific Ocean.

Alex Mustard / Detail of Light-bulb sea squirts (Clavelina lepadiformis), Swanage, Dorset, UK, English Channel.

Alex Mustard / Group of amphipods (Aristias neglectus) and (Leucothoe spinicarpa) living on a Gas mantle sea squirt (Corella parallelogramma), Loch Linnhe, The Highlands, Scotland, UK.

Alex Mustard / Group of Long clawed squat lobsters (Munida rugosa) shelter in a crevice in a wall, covered in Sea vases (Ciona intestinalis). Kinlochbervie, Sutherland, The Highlands, Scotland, United Kingdom. Loch...

Franco Banfi / Seafan / Red gorgonian (Paramuricea clavata) and Light-bulb sea squirt (Clavelina lepadiformis) Punta Carena, Capri Island, Sorrentine Peninsula, Italy, Tyrrhenian Sea, Mediterranean.

Franco Banfi / Red sea fan (Paramuricea clavata) with gorgonian corals and Light-bulb sea squirt (Clavelina lepadiformis) Punta Carena, Capri Island, Sorrentine Peninsula, Italy, Tyrrhenian Sea, Mediterranean.

Franco Banfi / Red sea fan (Paramuricea clavata) with gorgonian corals and Light-bulb sea squirt (Clavelina lepadiformis) Punta Carena, Capri Island, Sorrentine Peninsula, Italy, Tyrrhenian Sea, Mediterranean.

Georgette Douwma / Golden sea squirt (Polycarpa aurata), Stalked green ascidian (Oxycorynia fasciatus) and Stalked ascidian (Clavelina robusta). Lembeh Strait, North Sulawesi, Indonesia.