Draw a modified “S” for the foundation of the body and build on the curves to suggest the body’s form. Sketch the fin.

Add the spines on the head, the plates on the body, and the eye.

Refine the lines, erasing when needed, and further define the body plates.

Darken the lines and shade with parallel hatchmarks. Pull out highlights with a kneaded eraser where necessary and add a few bubbles escaping from the mouth for good measure.