I've observed quite a few of these transparent shells washing up recently. They look like small, oblong, sparkling crystals on the beach. I don't remember seeing so many before (e.g., ~25 over a 300-ft stretch of beach), although it's possible I just haven't noticed. I'll have to keep better notes!
Reviewing the photos I started wondering about the tubercles. I often think of spines like this being deterrents to predators. But if this is an internal shell, why do they have tubercles?
Some smaller individuals, ~1 cm long, have also been washing ashore (see next photo).
Finding smaller individuals made me think about reproduction in this species. Online there are several sites that state Corolla lays strings of eggs. But I'm wondering — How do males and females find each other at sea? What do the juvenile stages look like? How fast do they grow? How long before they become mature? Is this a typical time of year to find smaller individuals? And is there something about recent water conditions that's driving more of them on shore right now? (Seawater temperatures have been relatively warm, ~12.5-13.5°C.)