An aquatic creature made of a yellow goo moves through the water by moving its body like a squid. The goo can slowly dissolve small creatures and the planet's form of seaweed/kelp. It also has an adaptive protective layer around the goo that can strengthen areas that need extra protection. The goo is highly nutritious to nearly all forms of aquatic life. The only way to bypass the protection is to come at the creature at high speed and breach the protection, not allowing it time to strengthen.
How would an aquatic creature co-evolve to feast on the goo?
*The goo would have to be extracted from the creature before it is eaten, otherwise the creature could dissolve the predator's digestion system.