Final answer:
A mollusk larva is called a trochophore, and it is covered in cilia that enable it to swim. This is an early developmental stage in aquatic mollusks.
Step-by-step explanation:
The mollusk larva covered in cilia to help it swim is known as a trochophore. This early developmental stage in aquatic mollusks features several bands of cilia that provide locomotion. The trochophore stage precedes other potential stages like the veliger larva in the life cycle of some mollusks. As the larvae mature, they will undergo metamorphosis into the adult form. Mollusks are characterized by a muscular foot, the mantle which can secrete a shell in many species, and in most cases, respiration facilitated by gills or ctenidia in aquatic species.