The collar seemed to be left off to introduce a narrow white chemisetted effect slightly puffed of white batiste inside the neck.

The Martuthunira visited the islands of the Dampier Archipelago, which they presumably shared with the Yapurarra/Pijurru, and the Mary Anne Group.

to retrench bastions

You might not suffer from thalassophobia or submechanophobia, but you'll certainly experience what that's like while exploring Subnautica's alien depths.