This pretty ribbon-like creature is the Red-tipped Flatworm (Pseudoceros bifurcus). It is a marine flatowrm in the polyclad flatworm family Pseudocerotidae. While they do resemble our beloved nudibranchs, they are not actually related to them or other mollusks for that matter.
These creatures are thin and delicate but their personalities aren’t so dainty. Red-tipped Flatworms, along with all other flatworms for that matter, are active carnivores and scavengers, using their proboscis to feed on dead or injured animals and colonial animals such as bryozoans and soft-corals.
To move around, the flatworms use their hairlike cilia to propel them along the bottom of the sea floor. When disturbed, they are capable of swimming short distances by undulating their body like a wave for a quick getaway.