While sampling marine plankton in a lab, a student encounters large numbers of fertilized eggs. the student rears some of the eggs in the laboratory for further study and finds that the blastopore becomes the mouth. the embryo develops into a trochophore larva and eventually has a true coelom. these eggs probably belonged to a(n)

mollusc                                    

Explanation:

           A mollusc is one of the largest group of phylum, Mollusca of invertebrate. They have very soft bodies but they don't have legs. Their body does not have ring like segments as other worms. Most of them have tentacles which they use to grab things and move.

          Most of the mollusc family lives in the oceans. Very few of them can also live on the lands.

          The life cycle of a  mollusc begins with the larva when the eggs fertilizes. The opening at the central cavity of an embryo begins to form the mouth of the mollusc where as the embryo grows to become s soft and translucent mollusc larva called the 'trochophore'.  The trochophore has cilia and rings that gives them the shape of a rotating wheel.

Therefore the answer is ---

mollusc

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