PROTISTA, EUBACTERIA, & PORIFERA

From Stanley (1993)


Kingdoms EUBACTERIA and PROTISTA

Fossil organisms within the Kingdom Protista represent the earliest life forms known. These organisms are characterized by a single-celled body plan and are contrasted to members of the Kingdom Eubacteria (green and blue-green algae) by having a nucleus. This lab concentrates on the protist phyla Foraminifera and Diatoms because many of their constituents 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. During this lab you will become familiar with the morphologic features and be able to identify each of the groups listed below, in addition to knowing their geologic ages.

The recepatulitids are included here because they are now believed to belong to the Chlorophyta or green algae within the simply organized Kingdom Eubacteria even though they were once thought to be related to sponges.


CLASSIFICATION & GEOLOGIC RANGES

Kingdom Eubacteria (Precambrian - Recent)

group "stromatolites" (Archaen - Recent)

Kingdom Protista (Precambrian - Recent)

group "receptaculitids" (Ordovician - Devonian)

  Phylum Granuloreticulosa

Class Foraminifera (Cambrian - Recent)
      group "fusulinids"(Late Paleozoic)

group "nummulitids"(Early Cenozoic)

      "planktonic forams" ( Cretaceous-Rec.)

Phylum Acrtinopoda

Class Radiolaria (Cambrian - Recent)

Phylum Chrysophyta

"diatoms" (Cretaceous - Recent)

 


Kingdom Eubacteria

"Stromatolites"

Stromatolites are organically produced sedimentary structures and are amongst the oldest fossils known on Earth (they occur in Archean rocks 3.5 b.y. old!). 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.


Kingdom Protista

"Receptaculitids"

Receptaculitids are a type of Dasycladacean green algae (Phylum Chlorophyta). They are characterized by thick calcareous sheets, plates, or sometimes as balls or discs that are perforated by numerous holes arranged in an orderly (usually spiral) fashion. The holes are in fact external molds of the plant's soft stems and not body fossils at all.


Class FORAMINIFERA

Foraminifera are the most common and geologically most important of the fossil protozoans. The name translates to pore-bearing and refers to the numerous perforations (foramina) in the skeleton walls. It is through the foramina that the organism extends its pseudopod or protoplasm.

Today, nearly all forams live in marine environments and are either bottom dwellers (benthonic) 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 (CaCO3) 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.


Test Composition and Microstructure

Agglutinated (sometimes called arenaceous). These tests are composed of grains or fragments of foreign material cemented by the organism and commonly have a sugary appearance. Occasionally grains of quartz and/or shell fragments can be seen.

Calcareous tests can either be hyaline which can be distinguished by their glassy appearance or porcelainous which are usually white or opaque in color and resembles china or porcelain.


Test symmetry

1. Uniserial. Chambers are added in a straight or curvilinear series. (see Figure 1 below)

2. Biserial. Chambers are added in an alternating fashion.

3. Triserial. Chambers are added every 120o in a spiral fashion.

4. Planispiral. Chambers are added around the periphery and are coiled in a single plane. Planispiral tests are evolute when all previous chambers are visible, and are involute when only the last spiral or whorl is visible.

5. Trochospiral. Chambers are added around the periphery, but each new chamber is slightly offset so that a very low spire or cone results. The central part of the disc on the side of the aperture is called the umbilicus.


Figure 1 - Foraminifera Test Morphology

From Boardman et al (1987)


Ecology

During life, forams are either benthonic of planktic, relying on their pseudopodia for both locomotion and creating water currents for food gathering.

Benthic forms inhabiting shallow to deep water environments can be recognized by their larger size, thick heavily ornamented walls, and less "globular" shape.

Planktic forams are recognized by their thin, and often perforated, tests and globular inflated chambers. You should be able to recognize the difference between the two types of forams.


Larger Foraminifera

Several times during the history of Foraminifera, tests many times larger than you have been seen until now have evolved. Although large tests are known from several foraminiferal families, only two, the fusulinids (Family Fusulinidae) and nummulitids (Family Nummulitidae) are considered below.

The nummulitids existed during the Early Cenozoic and are famous for their abundance in limestones from which the Great Pyramids of Egypt built. Their tests are planispiral and involute, and unlike the fusulinids, are coiled around the short axis. Examine this specimen from Egypt.

The fusulinids were important benthic constituents of Late Paleozoic shallow seas. The tests of fusulinids are involute and planispirally coiled about the long axis. The test walls of fusulinids are multi-layered in contrast to the microgranular tests of other forams. An individual fusulinid can be seen in this image. A good example of a fusulinid limestone can be seen in this image.


RADIOLARIA

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 (there are minor groups which construct their tests of strontium sulfate a silica enriched with organic material). Like the foraminifera, radiolarians have pseudopodia which protrude through the porous tests to aid in locomotion and food gathering. The tests of radiolarians exhibit great morphologic diversity, but they are typically characterized by radial or spherical symmetry. Examine this microscope image.


Phylum CHRYSOPHYTA

"Diatoms"

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.

Diatoms occur in two basic forms: (i) the centric type in which the test has radial symmetry, and (ii) the pennate type in which the test is elongate and has bilateral symmetry. An example of both types can be seen in this microscope image.

The centric type are planktic and predominantly marine, whereas the pennate type are mostly benthic and occur in fresh, brackish, and shallow marine environments. Sometimes diatoms form a rock called diatomite, which is composed entirely of diatoms. Diatomite often forms by a diatom "bloom" in nutrient-rich fresh-water lakes.



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Phyla PORIFERA & ARCHAEOCYATHA


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