Pink-centered Zooanthids
(Phylum Cnidaria, Class Anthozoa, Order Zooanthidae. See Overview of Cnidarian Diversity)
This zooanthid has pink-centered polyps interconnected by a continuous mat of living tissue that encrusts the rock they are growing on.
About zooanthids:
Zooanthids are anemone-like anthozoans that usually grow in colonies. In some species the polyps separate from each other almost completely after budding off from each other, while in other species the polyps are all interconnected by a continuous mat of tough, rubbery/leathery living tissue.
Like nearly all of the other cnidarian species in our aquaria, these zooanthids depend on the products of photosysnthesis from their zooxanthellae for most of their nutrition. (zooxanthallae are symbiotic algae that live in their tissues)