Siphonophores: the longest animals on the planet – in pictures

This siphonophore, physonect siphonophore Stephanomia sp., can reach 10 meters in length. It is a colony of specialised individuals called “zoids”. Around the periphery are stinging filaments used to catch prey Photograph: S Haddock/MBARI Photograph: S. Haddock/MBARI Physalia the “Portuguese man of war”. The siphonophore Physalia physalis is made of hundreds of reproductive, digestive and fishing zoids beneath a float – a “pneumatophore” – serving as a sail to move at the surface of the ocean. Its fishing zoids can extend several meters. They are studded with cells containing stinging, venom-filled nematocysts which can paralyse prey and even kill humans Photograph: C Dunn/Brown University Photograph: C. Dunn/Brown Univ. Feeding polyps of a calicophoran siphonophore. These polyps are made of a filament carrying the digestive zoids – the gastrozoids – which contain yellow lipid droplets and, prey-catching zoids with reddish stinging cells Photograph: C Sardet/Tara Oceans/CNRS Photograph: C. Sardet/Tara Oceans/CNRS Stolon of the siphonophore Stephanomia sp. The stolon is a stem along which the different zoids are arranged. We see here feeding polyps Photograph: S Haddock/MBARI Photograph: S. Haddock/MBARI Gastrozoids of the siphonophore Apolemia sp. Some siphonophores have complex assemblages of specialised polyps including gastrozoids, dactylozoids and prey-catching filaments Photograph: C and N Sardet/CNRS Photograph: C. and N. Sardet/CNRS Nectophores of the siphonophore Stephanomia sp. Nectophores are a series of medusae/bells that contract to move the colony Photograph: S Haddock/MBARI Photograph: S. Haddock/MBARI The siphonophore Hippopodius deploys prey-catching filaments. Hippopodius hipopus extends and retracts several polyps covered with stinging cells to catch prey Photograph: C and N Sardet/CNRS Photograph: C. and N. Sardet/CNRS Male and female gonozoids of a calycophoran siphonophore. A Lensia conoidea male gonozoid expulses sperm on the left. Eggs are packed inside a female gonozoid Photograph: C and N Sardet/CNRS Photograph: C. and N. Sardet/CNRS Female gonozoid of a calycophoran siphonophore. A Lensia conoidea female gonozoid expulses an egg on the left. Sperm are packed in a pouch inside a female gonozoid Photograph: C and N Sardet/CNRS Photograph: C. and N. Sardet/CNRS Egg of a calycophoran siphonophore. A Lensia conoidea egg attracts sperm of the same species around the fertilisation site Photograph: C and N Sardet/CNRS Photograph: C. and N. Sardet/CNRS