As part of your independent study in field biology, you are sent to a small, inland sea. In one of your samples, you discover a small eel-like creature. It has a stiff, rod-shaped structure running the length of its dorsal side, with a line of nervous tissue running along with it. You would begin the process of classifying this organism by placing it in phylum:

A)Vertebrata.
B)Arthropoda.
C)Chordata.
D)Cnidaria.
E)Mollusca.