FOSSIL INVERTEBRATES/Corals and Other Cnidaria 329 and, ultimately, by calical centres set in continuous colonial tissue (amural (Figure 8F and 8G), coenenchymal (Figure 9I and 9J) and plocoid (Figures 10G, 11A and 11B in ramose growth forms)) In the Rugosa and Tabulata, individuals are still sufficiently well defined to suggest that polyp integration was restricted to neural connectivity in most cases and only rarely was there confluence of body cavities However, some massive and branching tabulates have tubes or pores connecting adjacent corallites (Figure 9A and 9B), suggesting interconnected gastric cavities In some Scleractinia, separation of polyps may be more or less incomplete, resulting in small clusters (polycentric phaceloid; Figure 11B) or linear series (flabellate, meandroid; Figure 10F) of mouths opening into a single gut and surrounded by a single series of tentacles Corallite structure in colonial corals is either relatively invariant or restricted to a well-defined and narrow range at species level and often also at generic level Growth form is more variable In the past, it has been considered to reflect environmental influences, but increasingly the importance of underlying genetic controls has become apparent, at least for some corals Coral Ecology and Palaeoecology Scleractinia Living scleractinian corals range from the tropics to high latitudes (