Rare all-white O. bilamellata, faint trace of brown visible on gills. This form is often mistaken for O. muricata or Acanthodoris pilosa, but the thin ellipse of the gill ring stretching over about 60% of the body width differentiates O. bilamellata from them.
Track of slime left behind it on substrate as it travels.
Oosterschelde, Netherlands. May 2009 © A. Kuilman.