Monster Monday: Siphonophore, One and Many
April 18, 2016
At first glance, the siphonophore (sy FON uh fawr) is quite beautiful for a monster, though it is rather bizarre looking. Like jellyfish and corals, siphonophores are cnidarians (ny DAIR ee uhnz), a group of simple water animals armed with stinging tentacles. Some siphonophores resemble big jellyfish, while others take on stranger shapes. You might glimpse such a siphonophore in the dark ocean as a long, glowing chain, like a flowering vine or a jeweled necklace come to life.
Orange siphonophore
Credit: Hidden Sea Expedition 2005/NOAA/OAR/OER
Look closer, however, and you’ll see why the siphonophore is one of the strangest animals of all. A siphonophore begins life as a single wormlike polyp that develops from an egg. This polyp then begins budding off new structures called zooids (ZOH oydz). In some creatures, zooids take the form of new polyps. Others take on medusa forms—umbrella shapes, like jellyfish. Each zooid typically resembles an ordinary, individual cnidarian. But in a siphonophore, the zooids are genetically identical to the first polyp, and they stay attached to one another, like pearls on a string. So—is the siphonophore a single animal, or a group of genetically identical animals? Scientists dodge the question and simply call siphonophores colonial organisms. A siphonophore is both one and many.
Other animals—including bees, ants, and corals—live closely together in colonies, but the siphonophore takes colonial existence to an extreme. Zooids work like body parts. A siphonophore colony may use its medusa-shaped zooids as “fins” to swim through the water. Still other zooids have their own specialized tasks, like digestion or reproduction. If a siphonophore colony is disturbed, its zooids may break apart and float off on their own. However, individual zooids cannot survive. Only the colony can move, eat, and reproduce, which are the marks of a truly individual organism.
But is the siphonophore’s colonial existence really that strange? Look even closer—not at a siphonophore, but at yourself. Your body is made of trillions of cells. Many of these cells resemble other single-celled organisms that live on their own. But like the zooids in a siphonophore, your cells are all genetically identical to one another, having all developed from a fertilized egg. Within your body, cells take on specialized forms and work together to support a larger living structure—you.
