Life without a gut
Deep on the floor of the Gulf of Mexico, in total darkness, entire ecosystems are fueled by chemicals seeping from the earth. Here, at depths between 500 and 3,300 meters, live communities of exceptionally long-lived animals. The tube worms Lamellibrachia luymesi and Escarpia laminata form dense, bush-like colonies that can cover over 1,600 square meters of the seabed. Some of these individuals live for more than 250 years, reaching lengths of over 3 meters (nearly 10 feet).
These creatures are famous for what they lack: they have no mouth, no gut, and no digestive system. Instead, they depend entirely on a symbiotic partnership with bacteria living inside a specialized organ called a trophosome. This internal sac of tissue is packed with sulfide-oxidizing bacteria. The worm's body is a delivery system for these microbes. A bright red, feathery plume at the top of the body acts like a gill, absorbing hydrogen sulfide, methane, oxygen, and carbon dioxide from the water. The worm’s blood, which contains a specialized hemoglobin, transports these chemicals to the bacteria in the trophosome. The bacteria then perform chemosynthesis, converting the chemicals into organic compounds that nourish the worm.
An extreme and ancient existence
The hydrocarbon seep environment is inhospitable. Methane and hydrogen sulfide, which is lethal to many organisms, leak from fissures in the seafloor. The worms anchor themselves in these sediments with a posterior "root" structure, which can extend up to half a meter into the sediment to absorb sulfides directly. The soft body of the worm is protected by a tough tube made of chitin—the same material found in the exoskeletons of insects and crustaceans.
Determining the age of these animals presents a challenge, as they have no growth rings or other typical age indicators. Scientists estimate their lifespan by visiting seep sites years apart. Using submersibles, they stain a colony of worms with a blue dye. On a return visit a year or more later, they collect the worms and measure the new, unstained tube growth. By modeling these very slow growth rates and factoring in low mortality rates, researchers have calculated that Lamellibrachia luymesi can live for 170 to 250 years, while some individuals of Escarpia laminata may exceed 300 years. Their stable, predator-scarce environment and slow metabolism contribute to this longevity.