David Fleetham / Goby (Eviota sp) and juvenile porcelain crab (Pteroeides sp), on a Seapen. Komodo National Park, Indonesia.

David Fleetham / Porcelain crab (Porcellanella picta) hiding between the blades of the Seapen (Pteroeides sp). Komodo, Indonesia.

Alex Mustard / Common ghost goby (Pleurosicya mossambica) hiding in the branches of a sea pen (Pteroeides sp.). Anilao, Batangas marine protected area, Luzon, Philippines. Verde Island Passages, Tropical West Pacifi...

Alex Mustard / Common ghost goby (Pleurosicya mossambica) hides in the branches of a sea pen (Pteroeides sp.). Anilao, Batangas marine protected area, Luzon, Philippines. Verde Island Passages, Tropical West Pacific...

Pascal Kobeh / Three-lobed / Painted porcelain crab (Porcellanella triloba) in a Sea pen (Pteroeides or Pennatula sp) Sulu Sea, Philippines

Pascal Kobeh / Female diver taking a picture of a shrimp (Periclimenes sp.) living in a sea pen (Pteroeides sp.) Philippines, Sulawesi Sea.

Richard Robinson / Large sea pens (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Large sea pen (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Large sea pen (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Large sea pen (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Large sea pen (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Large sea pen (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Large sea pens (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Large sea pen (Pteroeides bollonsi) in Doubtful Sound, Fiordland National Park, New Zealand.

Pascal Kobeh / Commensal shrimp (Periclimenes magnificus) on Sea pen (Pteroeides), Manado, Indonesia. Sulawesi Sea.

Franco Banfi / Sea pen, (Pteroeides sp.) , Raja Ampat, Irian Jaya, West Papua, Indonesia, Pacific Ocean

Jeff Rotman / Sea pen (Pteroeides sp) in sand at night, Bismarck Sea, Papua New Guinea

Juergen Freund / Sea pen (Pteroeides sp) on seabed at night, Komodo NP, Indonesia.

Georgette Douwma / Sea pen (Pteroeides sp) on sandy sea bed. Komodo National Park, Indonesia

Georgette Douwma / Sea pen (Pteroeides sp) on sandy seabed, Komodo National Park, Indonesia

Georgette Douwma / Sea pen (Pteroeides sp) on sandy sea-bed. Komodo National Park, Indonesia

Georgette Douwma / Pen crab (Porcellanella triloba) resting in Sea pen (Pteroeides) to feed on plankton, Rinca, Indonesia

Georgette Douwma / Unidentified porcelain crabs (Pteroeides sp.) on Sea pen, Rinca, Indonesia

GEORGETTE DOUWMA / Sea pen {Pteroeides sp} Sangalaki, Indonesia

GEORGETTE DOUWMA / Sea pen {Pteroeides sp} Sangalaki, Indonesia

Juergen Freund / Sea pen (Pteroeides species} + diver, Sulu-sulawesi seas, Indo Pacific

Franco Banfi / Spiny sea-pen (Pteroeides griseum) on sandy seabed, Marine Protected area Punta Campanella, Costa Amalfitana, Italy, Tyrrhenian Sea.

Franco Banfi / Spiny sea-pen (Pteroeides griseum) on sandy seabed, Marine Protected area Punta Campanella, Costa Amalfitana, Italy, Tyrrhenian Sea.

Alex Mustard / Horned sea pen shrimp (Dasycaris ceratops) clambers through the branches of a sea pen (Pteroeides sp.). Anilao, Batangas marine protected area, Luzon, Philippines. Verde Island Passages, Tropical West...

Georgette Douwma / Sea pen (Pteroeides sp.) Lembeh Strait, North Sulawesi, Indonesia.