Mobility, growth patterns and substrate in some fossil and Recent corals

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Abstract
The relationships between mobile corals, the associated benthic fauna and the physical character of their substrates are analyzed. Different types of coral mobility are classified under 3 headings: passive rotation by water movement or by intervention of infaunal benthic or nektic organisms; lifelong towing by a symbiotic sipunculid worm; and auto-mobility, defined as self-induced movement which allows unburial, righting and lateral migration. In each case the morphology of the skeleton reflects the type of mobility, which can therefore be traced in the fossil record. Two examples of auto-mobile corals, Cycloseris (Recent) and Chomatoseris (= Anabacia) (Jurassic) are reviewed in detail; their main common architectural features are concentric growth and lack of epitheca. Both genera prefer loose, muddy sands. Mobility in corals allows them to flourish under circumstances unfavorable for sedentary forms. They are good indicators of loose, soft, sand substrates ranging from lagoonal through peri-reefal to deeper water environments. Though relatively few in species at any given time, mobile corals are geographically widespread and may be locally extremely abundant (> 1500/m2). World distribution maps are given for the Recent Cycloseris cyclolites, Diaseris distorta, Heteropsammia, Heterocyathus and Manicina areolata and for the Jurassic Chomatoseris.