The squid has been seen at several locations
The creature has been spotted in the Pacific, Atlantic and Indian Oceans, and in the Gulf of Mexico. One sighting was made at a depth of 4,734 metres (15,534 feet) - almost five kilometres (three miles) below the surface - in the western Atlantic, off the coast of Brazil.
The researchers behind the discovery say the find indicates how little we know about life in the Earth's largest ecosystem.
Independent sightings
The squid's arms are longer than those of any known squid species and held in an unusual position: spread outward from the body and then bent anteriorly.
The scientists speculate that the squid may be an adult member of the recently identified family called Magnapinnidae (which means "big fin"). Only juvenile squids in this family have been seen before. More research will be required, however, before the animals can be properly classified.
"I call it a mystery squid,'' said Mike Vecchione, a National Oceanic and Atmospheric Administration (Noaa) researcher and first author on the Science paper. "It's unlike any other squid I've ever seen.''
The assessment of the squid is based on photographs and video images taken by eight independent scientists from eight institutions in four countries.
'Spider's web'
"It is very distinctive with the very long skinny arms, with an elbow,'' said Vecchione. "There are 10 appendages there, but they all seem to be pretty much the same. In most squid, two would be tentacles.''
The scientist said he could not estimate the weight or mass of the animal but observed: "It is not like a giant squid, which has a really massive body. This is a fairly small squid with bizarre arms that stretch on forever.''
He speculated that the squid might use its long arms "like a living spider web" to catch its prey. "I think it dangles those arms until small organisms bump into them,'' he said. "It is like a snare.''
He said in one recent encounter with a submersible, the squid seemed to have problems dislodging its arms from the vessel's hull.