The Recent thecideid brachiopod Lacazella 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 genera Crania. Argyrotheca, and Megathiris belong 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 like Thecidea papillata (Schlotheim) and Danella recurvirostris (Defrance) seem to have acquired a free life, independent of the substratum, and others, like Praelacazella baltoviensis Barczyk stood fairly intense light in shallow water. Diptych thecideids and megathyridids occurred in bryozoan and coral environments.