Mystery invertebrate / egg casing?? Hutchinson Island, FL

This stuff was washed up all over the beach with Sargassum after a week or so of rough surf. It’s rubbery, and the cavities are hollow like bubble wrap. Some of them had little brown balls inside that look like roe. The vacated cavities all have a perfect oval hole that reminds me of an operculum. What is it?? I thought bryozoan at first but then I found some with the little egg things still inside….