I found these egg cases on a frond of feathery seaweed from Centennial Beach;
I was going to anchor the weed in my aquarium, without paying it much attention; it was just a tiny bit of fluff to serve as a hiding spot for amphipods. Then the light caught these yellowish jelly beads, a couple of millimetres long.
Here's one, propped against a light; ten eggs in a round case with an exit hole at the top. If you look closely, you can see horizontal grooves in the casing.
I don't know what lays these; possibly a snail, but which, I have no idea. If they hatch in my aquarium, I might find out. That's if the hermits and anemones don't eat the babies first.