Not the first time to see this, but, never capture it before.
The female is a very pretty worm. After her molting, male crs started to flying around crazily, and searching for her. It took some munites. At first, she rejected a lot of males ( she's really picky). We were so excited, hoping that a handson male could catch her. Finally, it is a crystal black. Not bad ^ ^.
And then the shell left behind became part of dinner,
That's a good source of calcium and magnesium.