Relatively large... uncertain about the ID, but specimen is very similar (to photos and drawings) seen here: https://www.arcella.nl/acanthocystis-turfacea/. Especially note the drawing depicting the 3 types of spine-scales, all of which are found in the current specimen.
A pond-edge water sample was collected on 4/8/2021 using a 10 micron dip net to enrich for microorganisms. Air temp. 65F