ferrugineus (Hyman, 1959)
Background color magenta covered with tiny white spots; inner marginal band red, outer marginal band bright yellow. This is one of the two most frequently seen flatworms in Hawai`i (along with Pseudoceros cf. dimidiatus). In my book I call it the "Fuchsia Flatworm." However, the large fuchsia-colored dorsal surface looks bluish at depth underwater. A camera strobe or flashlight will reveal it's "true" color, as in these photos. The species is active in the open by day and relatively common from Australia to Hawai`i.
The species name ferrugineus means "rusty" -- in reference to the red background color characteristic of specimens from the western Pacific. (The holotype is a specimen from Palau, Micronesia.) Hawaiian specimens are always magenta. Also, outside Hawai`i this worm often has ruffled margins. DNA studies might someday clarify the status of the Hawaiian population.
For the record,
Newman & Cannon give this color description, based on specimens
from outside Hawai`i: "Background body color dark red with white
dots. Dots always obvious. Inner margin red without dots. Rim wide,