<P> The microscopic shells of radiolarians are found in cherts of this age in the Culm of Devon and Cornwall, and in Russia, Germany and elsewhere . Sponges are known from spicules and anchor ropes, and include various forms such as the Calcispongea Cotyliscus and Girtycoelia, the demosponge Chaetetes, and the genus of unusual colonial glass sponges Titusvillia . </P> <P> Both reef - building and solitary corals diversify and flourish; these include both rugose (for example, Caninia, Corwenia, Neozaphrentis), heterocorals, and tabulate (for example, Chladochonus, Michelinia) forms . Conularids were well represented by Conularia </P> <P> Bryozoa are abundant in some regions; the fenestellids including Fenestella, Polypora, and Archimedes, so named because it is in the shape of an Archimedean screw . Brachiopods are also abundant; they include productids, some of which (for example, Gigantoproductus) reached very large (for brachiopods) size and had very thick shells, while others like Chonetes were more conservative in form . Athyridids, spiriferids, rhynchonellids, and terebratulids are also very common . Inarticulate forms include Discina and Crania . Some species and genera had a very wide distribution with only minor variations . </P> <P> Annelids such as Serpulites are common fossils in some horizons . Among the mollusca, the bivalves continue to increase in numbers and importance . Typical genera include Aviculopecten, Posidonomya, Nucula, Carbonicola, Edmondia, and Modiola Gastropods are also numerous, including the genera Murchisonia, Euomphalus, Naticopsis . Nautiloid cephalopods are represented by tightly coiled nautilids, with straight - shelled and curved - shelled forms becoming increasingly rare . Goniatite ammonoids are common . </P>

What was the environment like in the carboniferous period