Practice question

Vestimentifera are iconic deep-sea gutless siboglinid tube worms formerly considered separate phyla Pogonophora now reclassified within Family Siboglinidae Order Polychaeta, exemplified by giant tubeworm Riftia pachyptila reaching 2 meters at hydrothermal vents along East Pacific Rise. Adult body comprises vestimentum, trunk housing trophosome organ densely packed with intracellular chemoautotrophic sulfide-oxidizing gammaproteobacteria fixing inorganic carbon via Calvin cycle using sulfide oxidation producing organics translocated to host. Completely lacking mouth gut and anus, nutrition entirely dependent on symbiont metabolism host exchanges sulfide oxygen carbon dioxide via specialized extracellular hemoglobins binding both gases simultaneously preventing toxicity and supporting dense colonies at vents.