Dead among small boats. Probably left behind by fishermen
In an old shell of hexaplex trunculus: https://www.inaturalist.org/observations/212867967
possibly a ciliate? or a rotifer?? moving rapidly with what appeared to be a circular cluster of cilia (or fused cilia) at the flanged end. I couldn't keep up with it to get better pics or a video -- in area of intertidal silty sand next to Clube de Vela launch, marine waterway sheltered by a string of barrier islands
5cm