Excerpts from https://en.wikipedia.org/wiki/Riftia_pachyptila
Giant tube worms (Riftia pachyptila) are a species of marine invertebrate found in aphotic zones worldwide. Giant tube worms can live on the floor of the Pacific Ocean near black smokers, or hydrothermic vents, and can tolerate extremely high hydrogen sulfide levels. These worms can reach a length of 2.4m and a diameter of 4cm.
With sunlight not available directly as a form of energy, the tubeworms rely on bacteria in their habitat to oxidize hydrogen sulfide, using dissolved oxygen in the water as an electron acceptor. This reaction provides the energy needed for chemosynthesis. For this reason, tube worms are partially dependent on sunlight as an energy source, since they use free oxygen, which has been liberated by photosynthesis in water layers far above, to obtain nutrients. In this way tube worms are similar to many forms of ocean life which live at depths that sunlight cannot penetrate. However, tube worms are remarkable in being able to use bacteria to indirectly obtain almost all the materials they need for growth from molecules dissolved in water. Some nutrients have to be filtered out of the water. Tubeworm growth resembles that of hydroponically grown fungi more than it does that of typical animals which need to “eat”.
According to Wikipedia, “tube worms develop from a free-swimming, pelagic, non-symbiotic trochophore larva, which enters juvenile development, becoming sessile and subsequently acquiring symbiotic bacteria. The symbiotic bacteria, on which adult worms depend for sustenance, are not present in the gametes but are acquired from the environment via the skin in a process akin to an infection. The digestive tract transiently connects from a mouth at the tip of the ventral medial process to a foregut, midgut, hindgut, and anus and was previously thought to have been the method by which the bacteria are introduced into adults. After symbionts are established in the midgut, it undergoes substantial remodeling and enlargement to become the trophosome, while the remainder of the digestive tract has not been detected in adult specimens.”
The bright red color of the plume structures results from several extraordinarily complex hemoglobins. These tube worm hemoglobins are remarkable for carrying oxygen in the presence of sulfide, without being inhibited by this molecule as hemoglobins in most other species are.