<P> The common name "giant tube worm" is however also applied to the largest living species of shipworm, Kuphus polythalamia, which despite the name "worm" is a bivalve mollusc, rather than an annelid . </P> <P> Riftia develop from a free - swimming, pelagic, non-symbiotic trochophore larva, which enters juvenile (metatrochophore) 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 is introduced into adults . After symbionts are established in the midgut, it undergoes substantial remodelling and enlargement to become the trophosome, while the remainder of the digestive tract has not been detected in adult specimens . </P> <P> They have a highly vascularized, red "plume" at the tip of their free end which is an organ for exchanging compounds with the environment (e.g., H S, CO, O, etc .). The tube worm does not have many predators . If threatened, the plume may be retracted into the worm's protective tube . The plume provides essential nutrients to bacteria living inside the trophosome . Tube worms have no digestive tract, but the bacteria (which may make up half of a worm's body weight) convert oxygen, hydrogen sulfide, carbon dioxide, etc. into organic molecules on which their host worms feed . This process, known as chemosynthesis, was recognized within the trophosome by Colleen Cavanaugh . </P> <P> The bright red color of the plume structures results from several extraordinarily complex hemoglobins, which contain up to 144 globin chains (each presumably including associated heme structures). 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 . </P>

How do chemoautotrophic bacteria and archaea that live near hydrothermic vents obtain energy