The colossal squid was first described in 1925 based on specimens from the stomach of a commercially hunted sperm whale. A century later, an international voyage captured the first confirmed video of this species in its natural habitat – a 30-centimetre juvenile, at a depth of 600 metres near the South Sandwich Islands. Colossal squid can grow up to seven metres and weigh as much as 500 kilograms, making them the heaviest invertebrate on the planet. But little is known about their life cycle.

The footage of a young colossal squid in the water column was a serendipitous sighting, as many deep-sea squid observations are. It was seen during the live “divestream” feed of a remotely operated vehicle during the Schmidt Ocean Institute and Ocean Census partner expedition searching for new deep-sea species and habitats in the far south Atlantic. Those tuned into the stream had the remarkable experience of seeing a live colossal squid in its deep-sea home, although its identity was not confirmed until the high-definition footage could be reviewed later.

Predators such as whales and seabirds are still one of our best sources of information about the colossal squid (Mesonychoteuthis hamiltoni) because they are much better at finding it than we are. This partially explains why we have only just filmed this species in its natural habitat. Not only do these animals live in an enormous, dark and three-dimensional environment, they are also probably actively avoiding us.

Most of our deep-sea exploration equipment is large, noisy and uses bright lights. But the colossal squid can detect and avoid diving sperm whales, which probably produce a strong light signal as they swim down and disturb bioluminescent animals. The squid best able to avoid such predators have been passing on their genes for millions of years, leaving a current population of visually acute, likely light-avoiding animals.

The colossal squid is part of the “glass” squid family (Cranchiidae). In the Schmidt Ocean Institute footage, the characteristic mid-arm hooks needed for a positive ID are visible. For this young individual, the resemblance to other glass squids is also clear. With age and size, colossal squid likely lose their transparent appearance and become much more of an anomaly within the family.

At full size, the colossal squid may be a formidable predator, with its stout arms and array of sharp hooks, able to tackle two-metre-long toothfish. But in our first confirmed view of it at home in the deep sea, we can marvel at the elegance of this animal.

Until recently, few people were able to take part in deep-sea exploration. But now, anyone with an internet connection can be “in the room” while we explore these habitats and observe animals for the first time. It’s hard to overstate the importance of the deep sea. It holds hundreds of thousands of undiscovered species, it is probably where life on Earth started, and it makes up 95% of the available living space on our planet. This first confirmed sighting of a colossal squid inspires and reminds us how much we have left to learn.

The expedition that captured the footage of the colossal squid was a collaboration between the Schmidt Ocean Institute, the Nippon Foundation-NEKTON Ocean Census, and GoSouth (a joint project between the University of Plymouth, GEOMAR Helmholtz Centre for Ocean Research and the British Antarctic Survey).