The Trembling Nudibranch is another fairly common yellow, white, bluish/purple nudibranch — sharing its basic colouring and genus with both the Imperial and the Tom Smith. But unlike the Imperial, which has yellow spots against a white mantle, the Trembling is covered in white spots against a yellow mantle. Both have a purple/blue marginal line and both intially appear to have blue- tipped rhinophores and gills. Their behaviour and body shape is significantly different, so any amount of time with them will lead to a positive identification. The Goniobranchus vibratus actually vibrates — not just its gills as the Imperial and Tom Smith do, but its entire mantle. It literally seems to quiver as it moves. It is also a lot wider (sometimes bulked up or flat) than the imperial and gets to be a much larger size than the Tom Smith. To about 2.75″ or 70 mm. These individuals were all found in the rocky North Kihei/Maalaea area of Maui in water less than a metre to 8 metres.