Hexabranchus sanguineus was located on reef at a depth of approximately 20 feet. Length was not measured. Water temperature was 71 degrees F.

Note that locals consider this to be the distinct species, Hexabranchus aureomarginatus Ostergaard, 1955 (http://seaslugsofhawaii.com/species/Hexabranchus-aureomarginatus-a.html).