3.5 cm. White tubercles cover tan to lavender dorsum with varying networks of dark brown. White rhinophores and gills with yellow or green tips. Raise and lower front portion of mantle skirt as they crawl.
Seen during night dive in House Reef, Lankayan Island, Sabah.
''Goniobranchus geometricus'' is a species of colourful sea slug, a dorid nudibranch, a marine gastropod mollusc in the family Chromodorididae.