Many nassellarian radiolarians house dinoflagellate symbionts within their tests. He also made contributions in his morphological and systematic studies of radiolarians and tintinnids. "Phaeocystis" species are endosymbionts to acantharian radiolarians. Many Protozoa are zooplankton, including dinoflagellates, zooflagellates, foraminiferans, and radiolarians. The former presence of the sea is revealed by fossils of radiolarians and ammonites. Known life of Devonian Texas includes brachiopods, bryozoans, conodonts, corals, gastropods, radiolarians and trilobites. Major speciation events of radiolarians occurred during the Mesozoic. These may include fish, chaetognaths, krill, copepods, radiolarians, phytoplankton, nematocysts, ostracods and detritus. The microquartz is derived from the sclerae of sponges and the tests of radiolarians. These include sponges, ammonites, radiolarians, brachiopods, and the belemnite "Aulacoceras". Besides radiolarians sponge spicules are very prominent in these sediments. They commonly form from silica-secreting organisms such as radiolarians, diatoms, or some types of sponges. Finally, cercozoans include the Phaeodarea, marine protozoa that were previously considered radiolarians. Unlike true radiolarians, there are no cross-bridges between them. The remains of radiolarians are preserved in chert; a byproduct of siliceous ooze transformation.