Maritigrella eschara  Newman & Cannon 2000

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The above specimens were identified using the Hawaiian Polyclad Flatworms website, and NUDIPIXEL, the ID is tentative, the above specimens fit at least the description.
Pretty similar is Maritigrella fuscopunctata  Newman & Cannon 2000, also known as: Pseudoceros fuscopunctatus, or Eurylepta fuscopunctatus, which differs by orange spots in a honey comb pattern in the median region.
Let me quote Marcela Bolanos at LifeDesks:
"External morphology: Body oval and elongated, with a variable background of the dorsal surface from cream-white to grey-green with numerous, narrow and transverse black lines. Some of the lines are surrounded by gray continuous towards the middle of the body forming dark blotches in the median region which also is covered with large orange spots organized in line. The margin has some discontinuous and short lines." and: "Marginal tentacles, long, slender and held erected and two elongated cerebral clusters of eyes close to each other. A small, tubular, and muscular pharynx located anteriorly."