Favoritos de muir

It's horrifying and disgusting to see these mites on the ears of a mice caught by my kitten. I knew such mites could be found on the living bodies of some insects but didn't realize that they could live on a living mammal, in this case a mammal that might be alive just one or two hours before.
Poor mice, what a terrible life it lived...Everybody has its own 计生委 (Family Plan Committee) . For this mice, 计生委 were such mites and my kitten. For human beings, Hitler and Xitler are the most powerful 计生委, far more powerful than the mites, far far more disgusting than them.

This species has no records in ARCTOS for Alaska. I based my identification on the description in BugGuide which says: "Wings: Dark brown, covering about 2/3rds of the wing, lower dark margin step-like. The dark extends to the inner margin or anal cell. Three sets of cross veins have a light mark on each side of the vein, called aureoles. One near base, one about mid-wing, and another small one below (or R4 + R5, M2 and CUP)." On the second photo I have pointed out what I believe to be these aureoles.

I am not an expert, so I would love it for others to weigh in on this.

Will correct location when I know it. Unusually large specimen approx. 400 microns across. Due to the unusually inflated test, it may instead be an undescribed species. [edit: was actually a known species I hadn't previously encountered].
21 m depth.

10-15 mm
Found with Onchidoris bilamellata (coincidence?) under rocks at low tide. Quite common.

According to https://repository.library.noaa.gov/view/noaa/14990 there are 7 species of free swimming flatworms recorded from Alaska. Of these Nexilis epichitonius and Nesion arcticum do not reach this size and can be ruled out, as can Kaburakia excelsa which should be considerably larger. Acerotisa arctica seems to be known from only one species collected at Utquiagvik at the Arctic Ocean. I was not able to find any information about Notocomplana sanjuania or Notoplana longastyletta even under any of their synonyms.

Pleioplana atomata (also known as Notoplana atomata) seems like the most likely candidate. It is 9-28mm; found under stones and weeds in intertidal zone and matches iNat photos well.