Goniobranchus geometricus: This composite image shows four minor variations.
Upper left: The tubercles are low and spreading with each surrounded by a significant amount of off-white pigment. There are no small tubercles located in the meandering black region. The tubercles are essentially in two locations – medially between the rhinophores and gills and laterally around the mantle edge.
Upper right: The tubercles are higher and better defined. The black region contains smaller individual tubercles with reduced surrounding off-white pigment. The tubercles in the medial region are all linked by the off-white pigment surrounding the tubercle bases.
Lower left: This example is not unlike the Upper right specimen except the tubercles in the black region are much reduced to just a few very small spots
Lower right: The tubercles are very well-defined, separated and accentuated by the significant reduction of the accompanying off-white pigment around their bases. This reduction causes the black region to be much larger and dominant thus giving both the medial and lateral mantle regions a much darker appearance.

Goniobranchus geometricus: This composite image shows four more variations that present with many smaller tubercles in different arrangements.
Upper left: Tubercles are smaller and much greater in number. The off-white pigment is a light brown instead. The medial region exhibits a double diamond appearance created by the meandering of the black region that itself carries many small tubercles.
Upper right: The double diamond is very well defined. The black region is large and spreads almost to the mantle edge with fewer large tubercles. An overall darker appearing specimen.
Lower left: A profusion of small white tubercles all linked by their surrounding off-white pigment – brown closer to the mantle margin. The black region is reduced to a quite narrow meandering line.
Lower right: This specimen exhibits dark brown in lieu of black with light brown surrounding the tubercle bases. The medial tubercles are large and crowded forming a ridge.  The submarginal tubercles are also large but mostly form a continuous line.

Goniobranchus geometricus: This final example exhibits black rays radiating from the black meandering line to the very edge of the mantle and even transverse lines across the top of the notum.