Sponges, Cnidarians, and Ctenophores

Abstract

Sponges and coralomorphs were sessile epibenthic suspension feeders living in normal marine environments. Sponges with calcified skeletons, induding 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 coralomorph types indicates that during the Cambrian these groups, like other metazoans, evolved a variety of architectural fonns not observed in subsequent periods.