Rosy tritonia nudibranch

Rosy tritonia nudibranch (Tritonia tetraquetra)

This rosy Tritonia tetraquetra nudibranch was seen sitting on a marker at the Pinnacle, west of Southern Hydrate Ridge. It was near some soft corals, some of which were missing polyps, and had clearly been grazed on by this sea pen and soft coral specialist predator!
Photo credit: NSF-OOI/UW/CSSF, Dive R2228, V22

This large, pink nudibranch can be found all across the North Pacific, but has only rarely been seen around Southern Hydrate Ridge. These mollusks range from the intertidal down to ~700 meters depth and tend to be found on sandy seafloor, especially near sea pens and soft corals, their preferred food source. There are many similar species, but T. tetraquetra can be identified by its massive body (larger than similar species of nudibranch), depth of observation, and the frilly, intermittent set of latitudinal gill tufts along the margin of the dorsal surface.

References:
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0242103
https://www.mbari.org/know-your-ocean/revealing-the-secrets-of-sur-ridge/life-at-sur-ridge/

A deep-sea sole swims towards the ROV during a survey at Pinnacle, near Southern Hydrate Ridge. The marker on the left is from a previous expedition, and is now home to soft corals, rockfish and a nudibranch. Credit: UW/NSF-OOI/CSSF, Dive R2228, V22.
A deep-sea sole swims towards the ROV during a survey at Pinnacle, near Southern Hydrate Ridge. The marker on the left is from a previous expedition, and is now home to soft corals, rockfish and a nudibranch. Credit: UW/NSF-OOI/CSSF, Dive R2228, V22.
A rosy Tritonia nudibranch crawling over the seafloor next to a denuded bubblegum coral at Pinnacle, near Southern Hydrate Ridge. Credit: UW/NSF-OOI/CSSF, Dive R2228, V22.
A rosy Tritonia nudibranch crawling over the seafloor next to a denuded bubblegum coral at Pinnacle, near Southern Hydrate Ridge. Credit: UW/NSF-OOI/CSSF, Dive R2228, V22.
A rosy Tritonia nudibranch crawling on an old marker at Pinnacle, near Southern Hydrate Ridge. Credit: UW/NSF-OOI/CSSF, Dive R2228, V22.
A rosy Tritonia nudibranch crawling on an old marker at Pinnacle, near Southern Hydrate Ridge. Credit: UW/NSF-OOI/CSSF, Dive R2228, V22.
This rosy Tritonia tetraquetra nudibranch was seen sitting on a marker at the Pinnacle, west of Southern Hydrate Ridge. It was near some soft corals, some of which were missing polyps, and had clearly been grazed on by this sea pen and soft coral specialist predator! Photo credit: UW/NSF-OOI/CSSF, Dive R2228, V22.
This rosy Tritonia tetraquetra nudibranch was seen sitting on a marker at the Pinnacle, west of Southern Hydrate Ridge. It was near some soft corals, some of which were missing polyps, and had clearly been grazed on by this sea pen and soft coral specialist predator! Photo credit: UW/NSF-OOI/CSSF, Dive R2228, V22.