Echinoderms
ZeFrank
Beautiful sea cucumber swimming 1 min starts 25 sec
Enypniastes eximia video below
A swimming sea cucumber, Enypniastes eximia, was observed during NOAA’s expedition in the Gulf of Mexico, on 13 December 2017. The sea cucumber spends most of its time feeding off of surface sediments on the seafloor, but can swim if it wants to get somewhere more quickly or evade a predator. Common names for these holothurians include: “swimming sea cucumber”, “Spanish dancer” and “headless chicken monster”. Credit: Video courtesy of the NOAA Office of Ocean Exploration and Research, Gulf of Mexico, 13 December 2017
Defense system
Wikianimals, nice gallery at the end
https://wikianimals.eu/animals/sea-cucumber
Gallery of sea cucumbers, Joel Sartore:
https://www.joelsartore.com/keyword/sea-cucumber/
Larval form