Acorn worms were just one of the many types of strange fauna observed at a potential mud volcano site dubbed Twin Peaks, at a depth of 4829m.

Photographed 30 June 2016, Dive 13.

A type of jellyfish called a hydromedusa documented during midwater transects at 800m over a newly discovered petite-spot volcano – the first ever discovered in the U.S. Exclusive Economic Zone.

The water column is the largest biome on Earth and one of the least explored. According to the NOAA, almost every time scientists spend time documenting midwater fauna, they make new discoveries.

Photographed 5 July 2016, Dive 18.

This beautiful groppo (Grammatonotus sp.) was observed at Eifuku Seamount. At the top of the feature survey during this dive, small, colorful fish like this were very common among the rocks.

Photographed 25 June 2016, Dive 8.

A beautiful stalked crinoid, likely Proisocrinus ruberrimus, photographed on the upper slop of the Northwest Guam Seamount. The seamount sits within the last major unexplored seamount arc in the southern Marianas.

Photographed on 29 April 2016, Dive 8.

Cusk eel with unusual head shape: the large bulbous head features small eyes, large nostrils, and a mouth placed low on the head. This distinctive-looking animal, photographed on an unnamed seamount at a depth of more than 3000m, could be a new species.

Photographed 29 June 2016, Dive 12.

The anemone living on this parapagurid hermit crab (likely Parapagurus sp.) actually secretes a “shell” for the crab, which it inhabits instead of a gastropod shell (e.g., snail) that most hermit crabs call home.

This was photographed on 4 May 2016, Dive 13, at a unique geological formation called a serpentinite mud volcano, formed along faults associated with the subduction of the Pacific Plate at the Marianas Trench.

A tiny octopus made an appearance on Dive 19 at Esmerelda Crater, an active submerged volcano that is part of the Vents Unit of the Marianas Trench Marine National Monument. You can see how small the octopus is compared to the crinoid (sea lily) stalks it is next to.

Photographer 10 May 2016, Dive 19.

An oblique-banded snapper (Pristipomoides zonatus) and moray eel (Gymnothorax berndti) photographed at a depth of about 250m at a slope of Farallon de Medinilla, a small uninhabited island north of Saipan in the Northern Mariana Islands.

Photographed on 8 May 2016, Dive 17.

One of the unusual black corals (Schizopathes sp.) spotted on their side, making circles in the sediment at Explorer Ridge Deep at a depth of 2598m.

Photographed on 1 July 2016, Dive 14.

This long-tail red snapper was spotted on Pagan, one of the largest volcanoes in the Marianas Arc. 

Photographed on 19 June 2016, Dive 2.

An enteropneust (or acorn worm) leaving a characteristic fecal coil on the seafloor in Sirena Canyon, one of the deepest spots in the Marianas Trench, beginning at a depth of 4983m.

Photographed on 23 April 2016, Dive 3.

Cusk eel in the family Ophidiidae, photographed at a depth of more than 2000m at a Cretaceous seamount east of the Marianas Trench. This is in the genus Eretmichthys and may be the species E. pinnatus.

This bizarrely beautiful jellyfish was filmed at a depth of 3700m. The surreal footage was captured on 24 April while exploring the Enigma Seamount – named as such because we know so little about it.

See the footage and read more.

Footage of this 10cm-long ‘ghost-like’ transparent fish was captured on 5 July during an exploration of a ridge feature at a depth of around 2500m in the Marianas Trench.

View the footage and read more.

This ghost-like octopod is almost certainly an undescribed species and may not belong to any described genus. It was seen on the first operational dive of Okeanos Explorer’s 2016 season, on 27 February, at a depth of over 4000m northeast of Necker Island (Mokumanamana) in the Hawaiian Archipelago.