I’d get that checked out, if I were you.
Even if technically true, in the spirit of the quest for external asymmetry, these do not qualify. Those animals are very symmetrical externally.
Few mammal examples so far… How about the narwhal?
Here comes a bikini whale!
(Oops, wrong thread)
The OP title/question was about BILATERAL symmetry. The animals I named have a different type of symmetry and are not bilaterally symmetrical.
Fair enough, but my point still stands. In the spirit of the question, and almost every answer given, highly symmetrical animals are the EXACT OPPOSITE what is sought.
But they DID evolve from bilaterally symmetrical animals, and their larvae are bilaterally symmetric! So their radial symmetry actually evolved secondarily, apparently going through an asymmetric stage.
Eta: gah, once more the “suggested threads” trick me into necromancy.
Are we actually sure about that? Maybe they were originally NOT bilaterally symmetrical and their larva later evolved it as a secondary characteristic?
Anyhow - the question wasn’t “creatures that didn’t evolve from bilaterally symmetric animals”, it was whether or not they themselves were bilaterally symmetric. Which they are not in their adult forms.
And if all else fails: sponges. They’re animals, but not externally bilaterally symmetric.
You mentioned two groups of organisms in your post, starfish and urchins, which are both echinoderms, and sea jellies, which are in the Phylum Cnidaria. The echinoderms are definitely evolved from bilateral ancestors, while the Cnidaria are primitively radially symmetric.
So… I was half right? 
But does the half that was right match the other half?
And I would argue that a starfish’s radial symmetry is in addition to, not instead of, its bilateral symmetry. There exists a plane along which I could cut a starfish that would leave the two halves mirror images of each other. There also exist four other planes along which I could do the same thing.
As @Riemann pointed out, there can also be radially-symmetric shapes that aren’t bilaterally symmetric, but those aren’t the shape of a starfish.
That’s not what we are talking about when we refer to bilateral symmetry in biology. Bilateral symmetry in animals refers to being right-left symmetric on one axis, not on multiple axes. While it may be true that radial forms can also be technically bilaterally symmetric, that’s not what the term means in a biological context.
I suppose it’s possible, but given what we know about their relatives on the tree of life, seems very unlikely. However- I wasn’t disagreeing with you, just sharing a fact I’d recently learned about sea stars and their relatives.
I didn’t notice the mention of jellies which yes are a different group entirely.
Yes, perhaps the best way to avoid the confusion between purely geometric considerations and evolutionary considerations is to stick to the strict biological definition of bilateral symmetry as having a unique plane of reflective symmetry. This then does exclude Cnidaria and Ctenophora which have radial symmetry and multiple planes of reflective symmetry. The distinguishing feature of Bilateria is the unique plane.
Evolutionarily speaking, it is believed that bilateral symmetry evolved when animals began to actively seek their food, rather than filtering it or trapping it as in sponges, jellyfish, and comb jellies. Moving over a substrate, locomotion is more efficient if the bottom of the body becomes differentiated for that purpose. Seeking food becomes more efficient if you concentrate your sensors at the front of the body, in the direction of movement. Once you have a top and bottom and a front and rear you have bilateral symmetry.
While some echinoderms such as starfish actively seek prey, they do so relatively slowly so having a specialized head end is not so important.
Yes, when talk about how bilateral symmetry evolved, what we mean of course is not a gain of symmetry but the loss of radial symmetry.
They are bilateria because they are born that way, as typical little bilateral swimmy-wormy critters. Then the starfish, urchin, or whatever grows on the infant’s left side (like a cancer) and eventually absorbs it. So an adult starfish is not bilateral, but is bilateria, all the same.
That’s a very concise explanation. Thank you.