This super rare squid is a deep sea mystery. We recently spotted not 1, but 5, in the Great Australian Bight

The mysterious giant squid was first spotted in Australian waters. My colleagues and I from CSIRO and Museums Victoria detail the meetings in our new research, published today in ONE Public Science Library.

There have been only a dozen sightings of bigfin squid worldwide in the past two decades. Ours happened more than two kilometers below the ocean surface in the Great Australian Bight, off the coast of South Australia.

For many people, the phrase “deep-sea squid” can evoke images of the giant squid, Architeuthis dux, or kraken with huge tentacles swimming in the ink-black water.

But there are dozens, if not hundreds, of other species of deep-sea squid and octopus (both members of the Cephalopoda class) equally mysterious.

First encounters with a slippery individual

For years, one of the only ways to sample the deep sea has been to fish the bottom of the sea with nets. This has often damaged the soft bodies of deep-sea organisms beyond recognition. These mutilated specimens are therefore difficult to identify and reveal little or nothing about the creatures.

Fortunately, new technologies such as remote controlled vehicles (ROVs) equipped with high-definition cameras allow scientists to see species as they have never seen before, offering a deeper insight into their shapes, colors and behaviors in the wild.

The enigmatic big fin squid, Magnapinna, is a case in point. When scientists first described the species in 1998, all they had to go through were a few damaged specimens from Hawaii.

The most distinctive feature of these specimens were the large fins (in the upper part of the body), which gave the squid its name. Years later, scientists exploring the deep Gulf of Mexico with ROVs realized they had stumbled upon Magnapinna in the wild.

They found that in addition to its distinctive fins, its arms had incredibly long filaments on the tips, making the giant fin squid unlike any they encountered.

These delicate filaments, which are mostly broken in the collected specimens, give Magnapinna an estimated total length of up to seven meters!

Mysterious creatures and where to find them

But despite deep-sea ROV investigations becoming more common, Magnapinna has remained elusive.

The handful of sightings have been as distant as the Central Pacific, the North and South Atlantic, the Gulf of Mexico and the Indian Ocean. This suggests a worldwide distribution.

However, the big fin squid had never been seen in Australian waters. That was until recently when our team took part in a major research project to better understand the biology and geology of the Great Australian Bight, through the Great Australian Bight Deepwater Marine Program.

On the CSIRO Investigator research vessel and the REM Etive charter vessel, we surveyed up to five kilometers below the water surface. Using nets, ROVs and other camera equipment, we have recorded hundreds of hours of video footage and discovered thousands of species.

During a dive, as we watched the video feed from the cameras far below us, a subtle shape emerged from the darkness. With large wavy fins, a small torpedo-shaped body, and long, streamlined limbs, she was unmistakably Magnapinna. We screamed and stopped the ROV to get a better look.

The meeting lasted about three minutes. During this time we were able to use parallel laser pointers to measure the squid’s length – about 1.8 meters – before it swam in the dark.

In total, we recorded five encounters with Magnapinna in the Great Australian Bight. Based on the measurements of the animals, we believe we have recorded five different individuals – the largest number of Magnapinna ever filmed in one place.

Most of the previous records have been of single Magnapinna, but our five squid were found all clustered close to each other. This could mean that they like the habitat they were found in, but we’ll need more sightings to be sure.

Inexplicable behaviors

The footage we captured offered new insights into Magnapinna’s ecology, behavior, and anatomy.

Previously, Magnapinna had been seen many meters from the sea floor standing upright, with arms outstretched and filaments hanging down. We are not sure what the specific function of this behavior is. It could be a way to find prey, similar to sticky, sucker-covered fishing lines.

During our trip, we saw the squid in a horizontal version of this pose, just inches from the sea floor, with its arms and filaments running behind. Again, we don’t know if this behavior is for traveling, avoiding predators, or another method of hunting for prey.

A miss with a camera gave us a very close up image of Magnapinna showing filaments that appeared to be coiled up like springs. This could be a means for Magnapinna to retract her filaments when needed, perhaps if she wanted to avoid damage, or wrap something she has captured.

Until now, only one other cephalopod, the vampire squid (Vampyroteuthis infernalis), has been known to wrap its filamentous appendages in this way.

We learned more about the mysterious big fin squid. But until we have no more sightings, or even an intact specimen, the questions will remain.

One thing we do know is that ROV detection has great potential for improving our understanding of deep-sea animals. With so much of the ocean around Australia yet to be explored, who knows what we will see coming out of the darkness next time?

This article was republished by The Conversation under a Creative Commons license. Read the original article.This story is part of Science X Dialog, where researchers can report the results of their published research articles. Visit this page for information on ScienceX Dialog and how to participate.