Burrowing Sea Cucumber (Massinium/Neothyonidium magnum)
Madidir III, Lembeh. In the next two pics I show how it starts retracting its tentacles as it feels me getting closer.
Video of the same sea cucumber:
You can see how it approached its tentacles to its mouth one at a time to get food.
Also known as Echinoderms, Burrowing Sea Cucumber and Sea Basket Sea Cucumber.
Found singly buried in the sand of shallow waters on sand and rubble areas.
They feed on plankton.
Length - 30cm
Depth - 0-40m
When feeding they fan out their "arms" and then one by one roll them in into their mouths to feed.
Genus synonym: Neothyonidium