ClipArt ETC
"a a, expanded polypes; b b, polypes withdrawn into their cells; c c, coral uncovered by flesh, showing the cells. In this the corals usually form thick stony masses; the stony rays of the cells are exceedingly numerous, and the cells themselves penetrate deeply into the mass of coral, although they are generally partially divided by imperfect transverse partitions." — Goodrich, 1859

Astrae virdis

"a a, expanded polypes; b b, polypes withdrawn into their cells; c c, coral uncovered by flesh, showing…