How do submarines know where they are?

We spotted this #bigfinsquid (genus #Magnapinna) with #ROVLittleHercules around 5,400 meters (17,716 feet) deep on the #abyssalplain in the waters of the Mariana Archipelago. Rarely seen on camera, this marine invertebrate is recognized by its distinct morphology, including perpendicular arms and tentacles that resemble elbows. Scientists understand the bigfin may be the deepest-dwelling of all #squid, as it’s been seen even below 6,000 meters in the hadal zone.