Close up of a monoplacophoran mollusk, which may be the animal responsible with the trails of ‘clean’ rock observed throughout the dive.

Close up of a monoplacophoran mollusk, which may be the animal responsible with the trails of 'clean' rock observed throughout the dive. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2017 American Samoa. Download larger version (jpg, 1.2 MB).

Dive 08: Return to "Utu" Seamount
February 23, 2017
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Dive 08: Holothurian

This holothurian, or sea cucumber, was seen on the seafloor of "Utu" seamount displaying an unfamilar posture. Scientists thought it may be a feeding posture, but weren't certain. Video courtesy of the NOAA Office of Ocean Exploration and Research, 2017 American Samoa. Download (mp4, 16.1 MB)

Today's dive took us back to "Utu" seamount. Located in the northern region of the American Samoa Exclusive Economic Zone, the seamount appears to be composed of two distinct structures – a pancake-shaped structure at the base and a steeper-sided volcanic structure on top. After exploring the crater wall of the shallower volcanic structure during Dive 06, today we explored the deep flanks of the seamount, starting at approximately 4,000 meters depth and targeting the blocky base upon which the shallower, younger volcanic structure is built. Geologic samples collected during the dive will help to define the age and origin of the seamount and its relationship to  hotspots in the region. Over the course of the dive, we saw a range of bottom types, including relatively flat, ferromanganese-encrusted surfaces; ferromanganese cobbles and pebbles; and pillow structures encrusted with ferromanganese deposits. Potbelly and stalked (Caulophacus) sponges were seen often, as were small ophiuroids. We collected two dead sponge stalks, both with crinoid and anemone associates. A truly exciting find during the dive was the observation of what appeared to be a monoplacophoran mollusk. This "living fossil" is mostly known from surveys of soft bottom abyssal plains and this represented the first time the organism was seen alive by any of the scientists participating in the dive. Attempts to collect a specimen were, unfortunately, unsuccessful.