Question

In early 1977, marine geologists aboard the research submersible Alvin descended into the Pacific Ocean along the Galápagos Rift, a divergent tectonic boundary near the equator. The primary objective of the expedition was geochemical and thermodynamic: researchers sought to measure hydrothermal heat flow and confirm models predicting convective circulation of seawater through newly formed oceanic crust. Prior theoretical models posited that cold seawater percolated into basalt fissures, was heated by underlying magma chambers, and subsequently discharged back into the benthic abyss as mineral-laden hydrothermal fluids.

Upon reaching the rift axis at a depth of roughly 2,500 meters, the expedition confirmed the presence of warm-water vents discharging fluid enriched with hydrogen sulfide, silica, and dissolved metals. However, the most startling discovery was not geological, but ecological. In an environment previously assumed to be an austere biological desert characterized by sparse populations dependent on the scarce, slow descent of organic detritus from sunlit surface waters, Alvin’s crew encountered dense clusters of novel megafauna. These communities included giant vestimentiferan tube worms lacking digestive tracts, large vesicomyid clams with red hemoglobin-rich blood, and swarms of previously unknown decapod crustaceans thriving around the thermal discharge fissures.

This discovery challenged the foundational ecological paradigm that solar radiation constitutes the indispensable primary energy source for all complex benthic ecosystems. Subsequent biological investigations revealed that these vent communities are sustained through primary production driven by chemolithoautotrophic bacteria. Rather than harnessing photon energy to fix inorganic carbon via photosynthetic pathways, these specialized microorganisms oxidize reduced chemical compounds—chiefly hydrogen sulfide dissolved within the hydrothermal effluent—to generate adenosine triphosphate and synthesize organic molecules. Some vent organisms, notably the giant tube worm Riftia pachyptila, maintain an obligate endosymbiotic relationship with these sulfur-oxidizing bacteria inside a specialized internal organ termed the trophosome, completely bypassing the need for an external ingestion mechanism or photosynthetic byproduct.

According to the passage, the giant tube worm Riftia pachyptila derives its organic nutrition through which of the following means?