I don;t know what they are - again :( But if I do them as a Wildlife Wednesday, I hunt around to try to find out. So let's see what I find!
Oh, so incredible. It's a Goose Barnacle. Here's the Australian Museum site with some info.
Goose Barnacles are closely related to crustaceans - crabs and lobsters - and the brown kind of feeler things you might be able to see coming out of the shell are 'legs' they use for feeding.
I love doing this column and actually finding out what these weird things I find are. It's all too easy to assume I know what it is and not really test myself to see.
Hee hee hee...just had to google sex and barnacles. OMG! Most barnacles are hermaphrodites. Male barnacles have the largest penis relative to body size in the animal kingdom. And they shoot sperm into the ocean, the female gathers it and fertilises her eggs. Here's the article - it's very clever :)