When a sea star has only one arm remaining (and often a portion of the central disc), and it regrows all of its other arms, it's called a "comet" because the original arm is so much larger and appears similar to the tail of a true comet traveling across the sky.
Sea stars in the genus Linckia are famous for this type of regeneration from a single arm, but we had never seen it in Pisaster ochraceus.
We searched the Internet for other photos of Pisaster ochraceus comets, but could only find one picture of a Pisaster giganteus comet — to see it, click here.
It's likely that comets in Pisaster ochraceus are rare. We're guessing that the juvenile Pisaster in this photo lost four arms due to Sea Star Wasting Syndrome and it's now regenerating them. Never give up!