Question

cnidaria - shape of life
who were the first animals to swim the worlds oceans?
sponges
jellyfish
worms
mollusks

Explanation:

Cnidarians, which include jellyfish, are among the earliest animals. Sponges are sessile (attached and not moving). Worms and mollusks evolved later in the evolutionary timeline compared to jellyfish in the context of swimming animals in the oceans. Jellyfish have a body structure that allows them to move (swim, though their movement is more of a pulsating motion rather than the complex swimming of some later - evolved animals) in the water.

Answer:

Jellyfish