BIONOMIC CHARACTERS OF ANTHOZOA 1013 



haiiki does not seem to mind mud or sediment, or even muddy 

 brackish water, growing on, and encrusting the stones at the mouth 

 of the Mangrove Creek, AustraHa, these stones being covered with 

 mud and sHme, and being washed over twice in the twenty- four 

 hours by muddy, brackish water. (Tenison- Woods.) A common 

 Red Sea coral, Stylophora pistillata, is recorded by Mihie-Edwards 

 and Haime from the intensely salt and dense waters of the Dead 

 Sea. 



The simple corals (Caryophyllia, etc.) are chiefly found on 

 muddy bottoms, often attached to a shell or other object resting on 

 the mud. The bathymetric distribution varies from shallow water 

 to a thousand fathoms or more. This method of life corresponds 

 well with what is known of the Paljeozoic Tetraseptata, which com- 

 'monly lived on a muddy bottom, with their bases not infrequently 

 showing signs of attachment to shells or other foreign objects. The 

 compound corals build heads or stocks often of great size and 

 weight. They are generally attached to stones, shells, or -to the 

 rock bottom and, through rapid increase by budding or division, 

 masses of great size may be formed over a small object of support. 

 Even on muddy bottoms a small object of support may serve as 

 the nucleus around which a coral mass will grow, which, as it in- 

 creases in size and weight, will sink to a greater or less depth into 

 the mud on which it rests. 



The typical compound or reef corals are very restricted in their 

 bathymetric distribution. They do not normally occur below fifty 

 fathoms, and the majority live in less than twenty fathoms of 

 water. Very many, indeed, live so close to the surface as to be 

 exposed at the lowest tides. A minimum annual temperature of 

 twenty degrees centigrade marks the regions in which most reef- 

 building corals occur, though in a few cases colder regions are 

 known to be inhabited by true reef-builders. In all seas, however, 

 which are subject to freezing, or are regularly invaded by floating 

 ice, reef-building corals cannot thrive, and hence the occurrence of 

 modern or ancient coral reefs is a reliable indication of a minimum 

 winter temperature above freezing. 



The reproduction of the Anthozoa is both asexual and sexual. 

 The asexual method is carried on by fission and budding, the new- 

 formed corallites usually remaining united with their parents, thus 

 producing colonial forms. In some cases, however, the buds become 

 free and begin an independent life (Fungia, Ralanophyllia, etc.). 

 New colonies, however, are mostly begun by sexually generated 

 individuals. From the fertilized egg develops a meroplanktonic 

 ciliated embryo, in appearance not unlike the planula of the hydro- 



