Siphonophore
The longest animal on Earth — which is technically not a single animal at all
Photo via Wikimedia Commons
Superpower
What looks like one animal is actually a colony of thousands of genetically identical individuals (zooids), each so specialized for a single function that none can survive alone. Some only swim. Some only digest food. Some only sting. Some only reproduce. No individual does more than one thing. The colony coordinates without a brain — nerve impulses propagate through shared tissue — and together they form an animal up to 40 meters long, longer than a blue whale.
Overview
Siphonophores are colonial hydrozoans — relatives of jellyfish — found in all oceans from the surface to the deep sea. Praya dubia, a deep-sea species, is among the longest animals ever recorded at up to 40m. The Portuguese Man-o'-War is also a siphonophore — not a jellyfish. What looks like a single creature floating at the surface is a colonial superorganism whose individual members (zooids) have become so specialized over evolutionary time that they've lost all capacity for independent existence. They've been called the most extreme example of individuality in biology — simultaneously one organism and many.
Found in
All major oceans worldwide, from the surface (the Portuguese Man-o'-War) to the deep ocean (Praya dubia and others). Deep-sea siphonophores are among the most commonly encountered animals in the mesopelagic zone, frequently seen by ROVs.
Things worth knowing
- 1
The Portuguese Man-o'-War is a siphonophore, not a jellyfish. The float (pneumatophore) is a single zooid whose only function is to be a gas-filled float. The stinging tentacles are other zooids whose only function is to sting. None can survive if detached.
- 2
Philosophers of biology use siphonophores to argue about the definition of an 'individual' — since every zooid in the colony is genetically identical, is the colony one individual or many? There is no scientific consensus.
- 3
Some siphonophore tentacle-zooids (dactylozooids) are born, sting a single prey item, and die — their entire existence is one act of stinging. They have no other function, need, or capacity.
- 4
Deep-sea siphonophores produce bioluminescent light when disturbed — ROV footage shows entire sections of deep ocean flickering blue-green as vehicles move through curtains of disturbed colonies.
- 5
A siphonophore doesn't grow like a normal animal — it buds new zooids continuously throughout its life, adding to the length of the colony. It is never 'finished' growing, and may theoretically have no maximum length.