Fossil organisms within the Kingdom Protista represent the earliest life forms known. These organisms are characterized by a single-celled body plan Kingdom Eubacteria (green and blue-green algae) have no nucleus. The protist phyla Foraminifera and Diatoms have mineralized skeletons and an extensive fossil record. Because of their wide-spread distribution and rapid evolutionary rates, many of the protists are excellent index fossils used in biostratigraphic studies.
FORAMINIFERA Foraminifera are the most common and geologically most important of the fossil protozoans. Today, nearly all forams live in marine environments and are either bottom dwellers (benthic) or float in the water column (planktic). Forams are characterized by multi-chambered tests which are built by addition of new chambers during life. Chambers are separated by partitions called septa (singular = septum), whose exterior expressions are termed sutures. Composition of the tests are either calcite (CaCO 3 ) or agglutinated (cemented foreign particles, e.g., sand or silt grains). The classification of Foraminifera is based on –(i) test microstructure, –(ii) test symmetry, and –(iii) aperture type.
Radiolarians and Diatoms Radiolarians are heterotroph protozoans which thrive in the upper layers of the seas. The protoplasm of radiolarians is surrounded by a test commonly composed of an intricate lattice work of opaline silica The tests of radiolarians exhibit great morphologic diversity, but they are typically characterized by radial or spherical symmetry. Diatoms are a kind of microscopic golden-brown algae that secrete siliceous tests (sometimes called frustules) consisting of two overlapping halves or valves that fit together. The walls of the tests are ornamented by pores, grooves, and ridges.
EUBACTERIA Stromatolites are organically produced sedimentary structures and are amongst the oldest fossils known on Earth They are made by cyanobacteria (often erroneously called “blue-green algae”, however, because the cells are prokaryotic, they should not be confused with true algae which are eukaryotes. Stomatolites are without skeletons (they are layers of sediment), and differ from some similar-looking sponges that have a mineralized skelton.
Archeocyathids Archeocyathids have been assigned by paleontologists to many different animal groups, primarily the corals and Pleosponges. Many researchers even referred to them to a distinct, separate Phylum, Archeocyatha. Recent investigations have proved pretty conclusively that archeocyathids were an early experiment in the Phylum Porifera--they are now generally considered an extinct type of calcareous sponge.
Archaeocyathids Archaeocyathids were sessile, marine organisms of shallow, tropical and subtropical waters that lived during the early Cambrian period about 550 million years ago. T hey were widespread in Cambrian seas throughout the world and were the first major reef-builders before the true corals
PHYLUM PORIFERA (sponges) Porifera means "pore-bearing". Exterior covered by tiny pores. Globular, cylindrical, conical or irregular shape. Interior may be hollow or filled with branching canals. Solitary or colonial. Skeletal elements are called spicules, and they may be separate or joined. Composition may be calcareous, siliceous or organic material called spongin. Geologic range: Cambrian to Recent. Mode of life: Attached to the sea floor. Most are marine.
SPONGES Sponges have an asymmetric body with no true tissues, or organs. They have two layers of cells. Flattened cells cover the exterior. Collar cells line the interior chambers. Collar cells move large volumes of water through body pores by their beating flagella. They also trap suspended food particles in their microvilli collars. Between the two layers of cells there is a semifluid matrix with needlelike structures for support. Sponges reproduce sexually and have a free-living larval stage. They also reproduce asexually by fragmentation or gemmules.Sponges
CONULARIDS CONULARIDS- Although there is some controversy in regards to the systematic position of the conularids, most workers today place them with the scyphozoan cnidarians. The exoskeleton of conularids is composed of chitin and in outline is pyramidal with four sides. The exterior surfaces of conularids normally have finely spaced longitudinal ribs. The interior of conularids may have thickenings or septa developed. In life, conularids lived attached apical end down to the substrate.