This week my female Kellet's whelk (Kelletia kelletii) started laying eggs. She's been doing this every summer for the past several years. She lives with one other whelk, presumably the father of her brood, as the eggs are both fertilized and viable even though I've never seen the snails copulating.
That's right, copulating. Whelks are predatory marine snails, some of which get quite large. My big female's shell is a heavily calcified 12 cm or so; she's a beefy mother! Her mate is smaller, but other than the size difference I wouldn't be able to tell them apart. Anyway, whelks copulate, with the male using a penis to transfer sperm into the female's body. Not very different from the way we humans do things, actually.
So at some point in the recent past my whelks copulated, and this week the female began depositing egg cases on the walls of their shared tub. I first noticed them on Monday, but she may have started over the weekend.
Those pumpkin seed-shaped objects are the egg capsules. Each is actually about the size and shape of a pumpkin seed and has a tough outer covering that contains 20-50 developing embryos. After the entire clutch is lain, which usually takes this particular female a week or so, the mom will leave the eggs to develop on their own.
I'll keep an eye on these eggs for the next week or so, and might be able to get some photos of the embryos and larvae as they begin developing. Keep your fingers crossed!