tbf there are some pretty weird looking creatures in the ocean even now. Like, would the giant deep sea Isopods really look that out of place next to stuff like Anomalocaris? We still have plenty of spiky worm shaped things living on the bottom of the ocean. And for the softer side of animals, would things like siphonophores really look that out of place in a lineup of Cambrian fauna, if placed there and shown to someone who wouldnt have the knowledge to recognize what they actually were?