The octopus, known as Vitreledonella richardi, has only a few visible features - its optic nerve, eyeballs and digestive tract - and has been rarely filmed, despite scientists knowing of its existence for more than 100 years.
Due to a lack of live footage, researchers have been forced to study the animal by analysing specimens found in the gut contents of predators.
Marine scientists aboard a research vessel for the Schmidt Ocean Institute, an oceanographic research group, captured two sightings of the octopus during their expedition near the Phoenix Islands Archipelago.
The researchers spent 34 days conducting high-resolution seafloor mapping of more than 30,000 square kilometres and video exploration of five additional seamounts.
“Working with scientists and local researchers, this expedition is a remarkable example of the frontiers of science and exploration that we are able to support,” Dr Jyotika Virmani, executive director of the Schmidt Ocean Institute, said in a statement on the trip.
“Live-streaming the dives gives us a glimpse of rarely seen and fascinating creatures such as the transparent glass octopus.
“By providing this platform to further the understanding of our ocean, we trigger the imagination while helping to push forward scientific insights and the protection of our underwater world.”
The research team’s underwater robot, named SuBastian, also captured footage for the first time of a rare whale shark that is thought to be more than 40 feet in length.
In addition, scientists witnessed unusual marine behaviour, such as crabs stealing fish from one another, during their 21 expedition dives - which totalled more than 182 hours of exploration on the seafloor.
“The Ocean holds wonders and promises we haven’t even imagined, much less discovered,” Wendy Schmidt, co-founder of the Schmidt Ocean Institute, commented on the research.
“Expeditions like these teach us why we need to increase our efforts to restore and better understand marine ecosystems everywhere – because the great chain of life that begins in the ocean is critical for human health and wellbeing.”