Mussels are a bivalve shellfish. The word bivalve refers to an organism which exists in two, semi-independent pieces attached together by a central ligament. Mussels exist in freshwater and saltwater varieties and tend to congregate together attached to rocks in formations known as beds. Mussels have proven themselves to be immensely successful organisms, sometimes too successful; when mussels were introduced into the Great Lakes in the 1980s their population quickly exploded and the animals began to clog water intake pipes and other man-made infrastructure in the lakes. The distinct markings of the mussel provides the artist with an interesting challenge in representing the different curves and colourations.
Draw a straight line that is about four-fifths of the total length you want the finished mussel drawing to be. At the top of the straight line, smoothly transfer into a sweeping curve which curves rightward. Continue this curve past its highest point and down the opposite side of the shape stopping at the same level as where you began the initial straight line. Distance between the two ends of the line should be equal to a quarter of the length of the initial straight line. At its widest point, the width of the shape should be equal to the length of the straight line.
From the bottom of the sweeping curve, begin drawing a sharper curve which extends below the starting point and is, at its lowest point, about one-fifth of the length of the straight line below the starting point. Smooth the curve and merge it with the bottom of the straight line. You now have a shape which looks something like a human ear, with the sharper curve you have just drawn being the ear lobe.
From the left-hand side of the lobe of the ear shape, begin drawing thin, closely compacted lines. These lines not only represent the actual markings that a mussel acquires as it grows, but also allows you to represent the ridge that runs from the right-hand side of the lobe, vertically upward, flattening out toward the top of the shell. The highest point of each line should be where it crosses this ridge. Continue drawing these lines emanating from the left-hand side of the lobe until your reach halfway up the shell.
From halfway up the shell, continue drawing lines, but make them slightly thicker and have them emanating from the edge of the straight line on the shell. Move each line minutely up the side of the straight line until the shell is covered with these curved lines.
Add colouration and shading to the lines. The colouring of a mussel follows the patterns of the lines on the shell, with some lines being darker and almost black while others are lighter blue to grey. The lobe part of the shell has a much lighter colour.
Draw extra detail, such as the stringy masses of seaweed which attach themselves to the surface of the mussel and the rough, pockmarked surfaces of tiny barnacles which also cling to the surface of the mussel's shell.