CHAPTER FOURTEEN Sponges and coralomorphs were sessile epibenthic suspension feeders living in normal marine environments. Sponges with calcified skeletons, including archaeocyaths, mainly inhabited shallow to subtidal and intertidal domains, while other sponges occupied a variety of depths, including slopes. | 14-C1099 8 10 00 2 13 PM Page 299 PART III Ecologie Radiation of Major Groups of Organisms 14-C1099 8 10 00 2 13 PM Page 300 14-C1099 8 10 00 2 13 PM Page 301 CHAPTER FOURTEEN Françoise Debrenne and Joachim Reitner Sponges Cnidarians and Ctenophores Sponges and coralomorphs were sessile epibenthic suspension feeders living in normal marine environments. Sponges with calcified skeletons including archaeocyaths mainly inhabited shallow to subtidal and intertidal domains while other sponges occupied a variety of depths including slopes. The high diversity of sponges in many Cambrian Lagerstätten suggests that complex tiering and niche partitioning were established early in the Cambrian. Hexactinellida were widespread in shallow-water conditions from the Tommotian some of them may have been restricted to deepwater environments later in the Cambrian. Calcareans pharetronids together with solitary coralomorphs thrived in reef environments mostly in cryptic niches protected from very agitated waters. Rigid demosponges anthaspidellids and possible axinellids appeared by the end of the Early Cambrian and inhabited hardgrounds and reefs from the Middle Cambrian. The overall diversity of sponge and coralo-morph types indicates that during the Cambrian these groups like other metazoans evolved a variety of architectural forms not observed in subsequent periods. RAPID DIVERSIFICATION near the Proterozoic-Phanerozoic boundary implies the mutual interactions of ecosystems and biotas. One of the most striking features in the distribution of Early Paleozoic sessile benthos is the poor Middle-Late Cambrian record Webby 1984 . The present contribution deals with the ecologic radiation of sponges and cni-darians. SPONGES Earliest Metazoans Sponges are a monophyletic metazoan group characterized by choanoflagellate cells choanocytes . Based on studies made by Mehl and Reiswig 1991 Reitner 1992
