Different species. The other one is an asterina/aquilonastra I would remove it because they can quickly become an infestation. Starfish can reproduce by either spawning or splitting in half. Reproduction with their legs is hard on the star and must be done perfectly with the central disk in tact. So it doesn’t happen unless the star feels threatened in a life or death situation or is extremely stressed as they are vulnerable waiting for their legs to heal and regrow. Spawning is a more common form of reproduction for most stars.
