Swimming Sea Cucumber
On our record-breaking submarine mission we spotted free-swimming Holothurians (sea cucumbers) twice. The species seems to be Enypniastes eximia, which feeds on the ocean floor, but can also swim freely in the water column, perhaps to avoid predators.
According to the Woods Hole Oceanographic Institute, this creature can be up to a foot in length. Specimens we observed were hovering mid-water, undulating their cape/hood to swim. The internal organs are clearly visible through the transparent body cavity in these photos as well. This was definitely one of the stranger creatures we have ever encountered.