332 FOSSIL INVERTEBRATES/Corals and Other Cnidaria Table Comparative features of the two ecological groups of the Scleractinia, the Rugosa, and the Tabulata Scleractinia Algal symbiosis Epitheca/ holotheca Solitary forms Colonial formsa Growth rates Zooxanthellate Azooxanthellate Rugosa Tabulata Present Lacking Lacking Lacking Mainly absent Present in some Almost universal Present in most