Mediaster Sea Star (likely Mediaster tenellus)
This sea star (shown to the left of a brittle star) has been observed on several occasions, living on the lava rocks in Axial Caldera. According to Chris Mah (Smithsonian National Museum of Natural History) this sea star has characteristics similar to members of the Genus Mediaster, which are common in the Pacific, most likely Mediaster tenellus.
References:
https://www.marinespecies.org/aphia.php?p=taxdetails&id=368837
https://echinoblog.blogspot.com/search?q=mediaster