Though this may really look like a nudibranch (and in particular one I’ve shared before), this is actually a juvenile sea cucumber – probably a Black Spotted Sea Cucumber (Bohadschia graeffei). One particular point you can use to spot the difference is the tube feet that sea cucumbers have but nudibranchs do not – you can see some of them as small yellow protrusions from the upper-right side of this little sea cuke.
