Living Foraminifera Inside the Tests of Large Deep-Sea Species: The Case of Pseudogaudryina Atlantica (Foraminifera, Globothalamea) in Southeast Brazilian Slope

Studies regarding the ‘hermit’ behavior within foraminifera are scarce and usually focused on soft-shelled specimens. While breaking the tests of Pseudogaudryina atlantica (Bailey, 1851) to check for stained protoplasm, other foraminifera were directly observed inhabiting its interior. In this short note, the assemblage found is described, with emphasis on a unique microhabitat on the slope of the Santos Basin (SB). Samples were collected during the summer of 2021 at a station located at a 1,000-m depth (24°15′15.12″S, 42°34′56.28″W). A density of 108 tests/20 cm3 of large P. atlantica individuals (≥500 µm) was found. Nearly 10% of the tests analyzed in this study served as shelters for living foraminifera. Most of these were agglutinated specimens from the family Saccamminidae Brady, 1884. This is the first direct observation of non-soft-shelled specimens inhabiting empty Globothalamea foraminiferal tests in a bathyal environment. Documenting these strategies helps researchers understand benthic marine ecology and diversity, highlighting an easily overlooked microhabitat.