i would dare to say it resembles this anenome the most
Stichodactyla mertensii Brandt 1835, Merten's (Carpet) Sea Anemone. Family Stichodactylidae. Folded disc exceeding a meter in diameter in some specimens. Lives on hard surfaces that it covers closely. Small pedal disc, striated with some color. Short tentacles (1cm) of uniform color. Close up and further back on specimens in Pulau Redang, Malaysia. other info on this species
The largest sea anemone, with over 1 m diameter. Disc shaped, with sometimes folded edges. Short and regular tentacles, 1-2 cm long, more spaced and longer in the central area and missing around the mouth. Green or brown tentacles, light brown column with orange or pink stains. Adhaesive verrucae under the oral disc edge hold the disc in position. . regeon: indo pacific
Found on rocky bottoms, along the reef front and external reef. Often the basal disc is fixed into crevices, and the whole animal can withdraw (although not quickly).
This is a species with zooxanthellae. Obligate association with anemone fishes (in our area Amphiprion clarkii, A. sandaracinos, A. ocellaris), also associated occasionally with the three spot damsel Dascyllus trimaculatus and with the porcelain crab (Neopetrolisthes oshimai).
simular species
Easy to confound with the 2 species belonging to the same genus, S. haddoni and S. gigantea. Apart from the less tightly packed tentacles, the easiest way to distinguish them is based on the environment: S. mertensii is always on rocky bottoms, S. gigantea and S. haddoni on the sand. hope this helps
looks like another smaller one just above it in the second picture.