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 anus. The embryo develops into a bilaterally symmetrical larva and eventually has a true coelom. These eggs probably belonged to a(n)

The question is incomplete as it does not have the options which are:

A) chordate.

B) echinoderm.

C) nematode.

D) mollusc.

A) chordate.

Explanation:

The animals can be distinguished based on embryonic development and are categorized into two types: Deutrostomes and the protostomes.

The deuterostomes are the organism in which the small opening in the embryo called the blastopore develops into the anus. The deuterostomes organism belongs to two groups of the animal: the echinoderms and the chordates.

The chordates are the animals which possess the bilateral symmetry that is can be divided into left and right sides and posses true cavity or coelom.

Thus, Option-A is correct.