Final answer:
Chemoautotrophs are autotrophic organisms observed in hydrothermal vents.
Step-by-step explanation:
Autotrophic organisms observed in hydrothermal vents are best described as chemoautotrophs. Chemoautotrophs are primarily bacteria and archaea that can synthesize complex organic molecules, such as glucose, for their own energy using inorganic molecules as an energy source. These organisms use hydrogen sulfide, released from the vents, as a source of chemical energy to carry out their autotrophic activities.