- These taxa consist of a broad array of organisms, including foraminifers, corals, bryozoans, mollusks, echinoderms, and fish.
- Basically what is available in the fossil record are only hard parts-bones and teeth for vertebrates, and shells for mollusks, arthropods and echinoderms.
- Some DNA-based studies of evolution suggest that hemichordates are actually closer to echinoderms than to true chordates.
- Included in this clade are three very different-looking phyla - the echinoderms, hemichordates and chordates.
- The fossil content consists of ammonites, belemnites, brachiopods, echinoderms, bivalves, crinoids, gastropods, ostracodes and benthic foraminifers.