1
Radiolaria and the Rock Record Radiolarians are important constituents of chert at certain times in geologic history. Their tests accumulate on the seafloor today to form radiolarian ooze, particularly in deep water, where any calcium carbonate shells would be dissolved.
Marine Invertebrates in the Paleozoic Seas The fossils of shell-bearing invertebrates that inhabited shallow seas are common in Paleozoic rocks. Archaeocyathids, sponges, corals, bryozoans, trilobites, molluscs, and echinoderms. Many were benthic (bottom dwellers), but others, such as graptolites, were planktonic. Currents carried them over wide areas. As a result, graptolites are useful index fossils for global stratigraphic correlation.
Phylum Archaeocyatha Name means "ancient cup" Chief characteristics: Conical or vase-shaped skeletons made of calcium carbonate. Double-walled structure with partitions and pores. Geologic range: Cambrian only. Extinct. Mode of life: Attached to the sea floor. Reefbuilders.
Phylum Porifera - The Sponges Name means "pore-bearing" Covered by tiny pores
Corals, sea fans, jellyfish, and sea anemones. Name: Cnidaria are named for stinging cells called cnidoblasts or cnidocytes. Many are soft-bodied but only those which form hard skeletal structures are readily preservable as fossils. Phylum Cnidaria
Phylum Cnidaria Geologic range: Late Precambrian (Proterozoic) to Holocene for the phylum. The first corals were the tabulates. Mode of life: Corals live attached to the sea floor, primarily in warm, shallow marine environments.
Phylum Cnidaria Chief Characteristics 1. Radial symmetry 2. Mouth at the center of a ring of tentacles.
Phylum Cnidaria Chief Characteristics 3. Body form may be polyp (attached to the bottom, with tentacles on top) or medusa (free-swimming, jellyfish).
Most rugose corals are solitary and conical (shaped like ice cream cones). Septae are visible in the circular opening of the cone. Some rugose corals are colonial, having hexagonal corallites with septae (such as Hexagonaria from Devonian of Michigan). Rugose Corals
Rugose Corals Geologic range: Ordovician to Permian - all extinct. Rugose corals were abundant during Devonian and Carboniferous, but became extinct during Late Permian.
Tabulate corals are colonial and resemble honeycombs or wasp nests. They lack septae. They have horizontal plates within the theca called tabulae. Tabulae are one of the main features of the tabulate corals. Tabulate Corals
Geologic range: Ordovician to Permian - all extinct. The principal Silurian reef formers. They declined after Silurian and their reef-building role was assumed by the rugose corals. Tabulate Corals
Modern Corals Modern corals are scleractinian corals. Scleractinian corals have septae are arranged in multiples of six, and are sometimes called hexacorals. Scleractinian corals did not appear until after Paleozoic Geologic range: Triassic to Holocene.
Phylum Bryozoa Name: Name means "moss" (bryo) + "animal" (zoa). Chief characteristics: Colonial (many microscopic individuals living physically united adjacent to one another). The individuals are called zooids, and they are housed in a hard "capsule" called a zooecium. The colony is called a zoarium.
Phylum Bryozoa Individual zooecia (plural of zooecium) are very tiny (about the size of a pin-hole, a millimeter or less in diameter). They are just large enough to be seen with the unaided eye. Bryozoans may be distinguished from corals because of the apertures in the skeleton are much smaller.
Phylum Bryozoa The bryozoan colony may resemble lace or a tiny net, may be delicately branching, finger-like, circular or dome-shaped. There are more than 4000 living species of bryozoans, and nearly 16,000 fossil species.
Phylum Bryozoa Geologic range: Ordovician to Holocene. Mode of life: Widespread in marine environments. A few live in freshwater lakes and streams.
Phylum Bryozoa Archimedes, from Mississippian rocks, has a corkscrew-like central axis with a fragile net-like colony around the outer edge.
Phylum Brachiopoda Name: Name means "arm" (brachio) + "foot" (pod). Chief characteristics: Bivalved (two shells), each with bilateral symmetry. The plane of symmetry passes through the center of each shell or valve. The two valves differ in size and shape in most. Sometimes the larger valve will have an opening near the hinge line through which the pedicle extended in life.
Phylum Brachiopoda Soft parts include a lophophore consisting of coiled tentacles with cilia. The lophophore circulates water between the two valves, distributing oxygen and flushing out carbon dioxide. Water movements caused by the lophophore also transport food particles toward the mouth.
Phylum Brachiopoda Mode of life: Shallow marine environments. Generally attached to the sea floor. Inarticulate brachiopods are known to live in burrows in the sediment. Brachiopods are filter feeders.
Phylum Brachiopoda Geologic range: Early Cambrian to Holocene. Very abundant during Paleozoic. A few species (belonging to only three families) remain today.
Inarticulate Brachiopods Primitive brachiopods with phosphatic or chitinous valves. No hinge. Spoon-shaped valves held together with muscles and soft parts. Lingula is a well known genus Geologic range: Early Cambrian to Holocene
Articulate Brachiopods Calcareous valves attached together with a hinge consisting of teeth and sockets. Geologic range: Early Cambrian to Holocene Spiny brachiopods (called productids) are characteristic of Carboniferous and Permian.
Phylum Mollusca Clams, oysters, snails, slugs, Nautilus, squid, octopus, cuttlefish Name: Mollusca means " soft bodied."
Phylum Mollusca Chief characteristics: Soft body enclosed within a calcium carbonate shell. A few, like slugs and the octopus, have no shell. Muscular part of body of clams and snails and some other groups of molluscs is called the foot.
Phylum Mollusca Geologic range: Cambrian to Holocene Mode of life: Marine, freshwater, or terrestrial. They may: swim, float or drift, burrow into mud or sand, bore into wood or rock, attach themselves to rocks, or crawl.
Types of Molluscs 1. Monoplacophorans (Neopilina) 2. Polyplacophorans or amphineurans (chitons) 3. Bivalves or pelecypods (clams, scallops) 4. Gastropods (snails and slugs) 5. Cephalopods (squid, octopus, Nautilus) 6. Scaphopods (tusk shells)