I know this mystery animal was challenging. Eric and I had a hunch about it, but we had several advantages. In the field, under a 10x hand lens, the "little pearls" looked like bubbles, indicating a possible float. The blue color was also worth paying attention to. And if you look very closely, you can see that some of them also have a darker ring at the perimeter. The most challenging thing about these animals was their size — most were under a millimeter across!
Here's one of our first views under microscope:
Now you'll be able to see some important features — tentacles below, a "skirt" with a darker rim, a clear float, and a sail at the top (in varying stages of development).
Here's an even closer view of the individual in the lower left corner:
It might be hard to recognize this animal at this size, and before it's fully developed. Eventually, the float will flatten out to a level platform with concentric circles, the sail will stiffen, and the shape of the sail will include a small pointed tip in the center.
Perhaps you've guessed by now that these are juvenile By-the-Wind Sailors (Velella velella)? We've observed them about this small once before, but we've certainly never seen so many tiny Velella stranded at once.
Here's one more view, showing the developing tentacles and hint of the central "mouth" hanging down in the center of the tentacles. [Note: In these pictures, the mouth is pointing up towards the top of the frame.]
If you're curious, we have included a short video clip (below). It highlights the movements of the tiny Velella — flexing its mantle (the "skirt" — by the way, the brownish color is from dinoflagellate symbionts), and contracting and expanding its developing sail.
P.S. Last spring, I posted some pictures of a juvenile Velella that was ~1 mm across. Follow this link to review that post, "Just learning to sail."
P.P.S. In the video, perhaps you noticed the edge of a Purple Sea Snail (Janthina umbilicata)? That's a story for another night!