The Recent thecideid brachiopodLacazella mediterranea(Risso), studied in the Mediterranean and on the Great Bahama Bank, shows a depth range of 20–150 m (optimum 50–95 m), determined by the need of subdued light. A hard substratum is essential for the cementing of the shell. Brachiopods of the generaCrania. Argyrotheca, andMegathirisbelong to the same ecological niche ‐ more or less dependence on light and substratum results in a differentiation of the species in biocoenoses as well and taphocoenoses. Several Mesozoic species are studied in coral, bryozoan, poriferan, and rudist environments. Species likeThecidea papillata(Schlotheim) andDanella recurvirostris(Defrance) seem to have acquired a free life, independent of the substratum, and others, likePraelacazella baltoviensisBarczyk stood fairly intense light in shallow water. Diptych thecideids and megathyridids occurred in bryozoan and coral environ
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