Organisms

Organisms

Diatoms

Diatoms are small eukaryotic plants with over 10,000 known species, constituting one of the major components of the phytoplankton in freshwater and marine environments. Traditionally, they have been regarded as beneficial to the growth and survival of marine organisms, and to the transfer of organic material through the marine food chain to top consumers and important fisheries. From 1993 onwards, however, evidence has accumulated that has progressively challenged the classic view that diatoms are good and harmless food items for copepods, the dominant constituent of the zooplankton, which sustain the production and growth of larval fish. Laboratory results in recent years have shown that some diatoms potentially reduce copepod egg viability up to 100%; at times, egg production rates are adversely affected as well. [1]

Green Algae

Chlorophytes are characterized by green photosynthetic pigments, including chlorophyll a and b, and also some ß-carotene and various xanthophylls. They usually store food as starches, which are also the building units for the cellulose that many use to construct their cell walls. Although there are a number of classes of chlorophytes, only three are important to paleontology. Members of the Class Chlorophyceae are more diverse in morphology and include unicellular to multicellular forms. They include groups that appear to be immediately ancestral to green vascular-plants; scholars believe that this group gave rise to higher plants. One group that usually is placed among the simplest green algae, the “calcispheres,” also is claimed by the foraminiferan taxonomists as simple calcareous foraminifers. These fossils first appeared in abundance during the Devonian (408 to 360 million years ago), were common through the Carboniferous, and became rare in the Permian. They typically have a calcareous granular outer wall and a radial calcitic inner wall. Other calcispheres, “radiosphaerids,” have a dark organic inner wall surrounded by a granular wall that passes outward into a rugose (wrinkled) outer layer of irregular, crystalline calcite blades. Several simple unicellular algal groups form “algal mats,” which are recorded from strata as old as Ordovician (500 to 438 million years ago). These include the freshwater desmids.[2]

Protozoans

Informal term for the unicellular heterotrophs of the kingdom Protista. Protozoans comprise a large, diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies and that show no differentiation into tissues. Formerly classified in the animal kingdom, they are now generally divided into five protist phyla: Mastigophora (the flagellates), Sarcodina (the amebas), ...