Pelagothuria

Background

Pelagothuria is somewhat unusual in appearance compared to other sea cucumbers, as it looks more like a jellyfish with a large umbrella-like swimming structure supported by a ring of around 12 highly modified oral tentacles. Its body is translucent with pale purple pigmentation, and the mouth is surrounded by around 15 short feeding tentacles.

The veil can be contracted like jellyfishes do, and is interrupted at the central ventral radius. The animal reaches around 16 cm in total diameter. Its swimming seems mostly passive, more like slightly controlled drifting.

Pelagothuria was described by Hubert Jacob Ludwig in 1893 based on trawled specimens collected in 1891 by the USS Albatross between the Gulf of Panama and the Galápagos Islands at depths of 605–3,350 m. It was not until 1989 that the first in situ footage was obtained via a scientific expedition in the Galapagos at 542 m deep off San Cristóbal Island, followed by a scientific review by John Miller and David Pawson in 1990. In 2011, the NOAAS Okeanos Explorer photographed what scientists first believed to be an unknown jellyfish, but the picture was formally identified in 2014 by Christopher Mah and David Pawson as Pelagothuria natatrix. A second observation was made in March 2017 by the same mission off the Samoa Islands at 443 m deep near Howland Island, identified by Steve Auscavitch, including high-resolution video of the animal swimming in the water column.