The bigfin squid (Magnapinna sp.) is the deepest known squid species in the ocean, having been sighted as deep as 6,212 metres (20,381 ft) below the surface. Their anatomy is unique among squids; their arms and tentacles are of equal length and identical, held perpendicular to the body in a fashion that resembles the strings of a marionette puppet with jointed elbow-like structures. Little is known about the life history or feeding strategy of this species, but the presence of long, draping arms and tentacles has lead scientists to postulate that they feed by dragging these appendages along the seafloor below and ‘fishing’ for prey on the great silt sea of the deep's Abyssal Plain! Their tentacles, which contain elastic filaments, may recoil when they come in contact with prey, drawing the food up towards the mouth. What it is exactly that they're eating remains a mystery.