actually, g. Chiragra rarely show up as hitchhikers. They usually are not found living in what is sold as live rock. They are targeted because they are relatively large and easy to collect.
One interesting note, however. When have you ever seen a small g. Chiragra less than about 4 cm. I've collected hundreds of g. Chiragra and it is unusual to find a small one. We don't understand the habitat that they live in for their first couple of years.
Roy