Step 1: Start from the larva itself, not the animal.
Tornaria is a tiny, transparent, free-swimming larva covered in bands of cilia used for both swimming and catching food particles.
Step 2: Notice which larger group its shape resembles.
Its ciliated-band body plan looks almost identical to the bipinnaria larva of starfish, which is why tornaria is often mistaken for an echinoderm larva at first glance.
Step 3: Recall which animal actually produces it.
Despite that echinoderm-like appearance, tornaria is the larval stage of Balanoglossus, a worm-like hemichordate that lives in burrows in marine mud and sand.
Step 4: Explain why the resemblance matters biologically.
This shared larval form is one of the strongest pieces of evidence linking Hemichordata to Echinodermata and Chordata within the larger deuterostome group, since larval anatomy often preserves ancient evolutionary signals better than adult anatomy does.
Step 5: Rule out the other animals listed.
Nereis is a segmented annelid worm that hatches as a trochophore larva, not tornaria. Aphrodite is a marine polychaete worm, again with a trochophore-type larva. Echinus is a sea urchin, an echinoderm whose larva is called pluteus, not tornaria. None of these three produce a tornaria stage.
Final Answer:
Tornaria larva belongs to Balanoglossus, option (2).