Favoritos de bogsnail

Female, broadcast spawning; several males releasing sperm nearby (separate observation). I am especially curious why some, but not all, of the eggs appear to be stuck together with a halo of tiny spines on them; if you know the answer, please let me know!

This is earlier in the year than expected: "In California, spawning occurs from March to May" (O’Clair and O’Clair 1998, Cowles 2005).

I am 100% certain of this location, and the identification seems very certain. I think this might be important, as it is a very rare species only found alive a few times in the last 6 years. the shape matches a species found in Australia. If it's that species, how did it get here? If it's the California native species, could this be an extended range? Introduced? New species, even??

Looks like a butter clam, with some sort of mutation to the shell. I've only ever seen this once in person, but oddly enough there is another observation of another butter clam shell with the same mutation, found in the same place. Maybe a local environmental factor causing irregular growth patterns?