Chapter 35:  Protistan Diversity and Taxonomy

 

I.  Introduction to the Protistans

A.     acritarchs:  putative eukayotic fossils about 2.1 byo

 

II.  Evolution of the Eukaryotic Cell

A.  Endosymbiotic theory

B.     Autogenous (endomembrane) theory

 

III.  Overview of Diversity and Features of the Protists

A.  Diversity of protists

1.   virtually all single cell eukaryotes belong in this group. There are single-cell, colonial, and multicellular types of protists.

2.   at least 5 monophyletic kingdoms can be described from this once single polyphyletic kingdom.

3.      binary fission or mitosis occur in many protists

4.      most live in aquatic (-like) environments

5.      many live in symbioses with other organisms

6.      many are planktonic

7.      most have undulipodia at some life stage

8.      all photosynthesizers have chloroplasts

 

IV.  Systematics and Phylogeny:

 

A.  Archaeprotista (amitochondrates)

1.      lack mitochondria; most have hydrogenosomes.

2.      Some major taxa are the diplomonads (Giardia lamblia), parabasalians (Trichomonas vaginalis), pelobiontids, amoeboflagellates, and microsporidians.

3.      Most are parasites, but some are free-living; microsporans are obligate intracellular parasites.

4.      most divide by binary fission.

B.   K. Euglenozoa:

1.      Includes the euglena and its ancestor the kinetoplastids).

2.      Euglenoids:  autotrophic, heterotrophic and mixotrophic.  Characteristics: anterior chamber from which two flagella emerge, a protein pellicle, and a carbohydrate storage molecule, paramylon.  Reproduction is asexual only.

3.      Kinetoplastids:  single, large mitochondrion called the kinetoplast and associated flagella.  Trypanosoma sp. causes African sleeping sickness

C.     K. Alveolata

1.   All have alveoli, and common ribosomal RNA sequences.  Alveoli function unknown although they may contribute to osmoregulation and/or bouyancy.

Some major taxa include:

2.   P. Dinomastigota:  Dinoflagellates among the most abundant marine plankton; can be photosynthetic or heterotrophic;  Some cause red tides;  Reproduction is a unique hybrid of mitosis and binary fission.

3.      P. Apicomplexa:  Apicomplexans, also known as sporozoans, are named for their apical complex of organelles arranged at one end of the cell;  all animal parasites including Plasmodium sp., cause of malaria.  This group is noted for its sexual life cycles which often require multiple hosts.

4.      P. Ciliophora (ciliates): Ciliates are mainly single-celled, bacteria eating, aquatic organisms; have macro and micronuclei types; practice sexual conjugation and divide by binary fission;  Paramecium sp.

5.      Foraminifera: Forams are exclusively marine; can be planktonic, attached or in sediments; feature pseudopodia; calcium carbonate or sand grain shells with many pores. White walls of Dover are sediments of mostly dead forams

D.  K. Chromista (or Stramenopila: flagellum hair)

1.  range from uni to multicellular; many have multiple flagella of unequal length; photosynthetic members of this group have chloroplasts derived from Rhodophytes. Characterized by their unusual hairy flagella.

2.      Diatoms (P. Bacillariophyta):  probably the most abundant eukaryote; usually the dominant group of phytoplankton in both freshwater and marine ecosystems; shells (or tests) of silica.

3.      Golden algae (P. Chrysophyta):  Carotene and xanthophyll photosynthetic accessory pigments give them their golden color; most are unicellular and biflagellated;  characterized by pectin/silicate cell walls.  Many are freshwater plankton, but some are marine.

4.      Brown algae (P. Phaeophyta): mostly marine, multicellular seaweeds; some are very large (kelp); cellulose cell walls; alternating (heteromorphic) generations; chlorophylls a and c are main photsynthetic pigments; a source of many commercial vitamins and minerals.

5.      Water molds (P. Oomycota):  unicellular or coenocytic (mycelia) chemoheterotrophs; zoospores (larva) are biflagellated (one is hairy); cellulose cell walls; Some are decomposers and many are plant parasites. Caused the potato blight in Ireland, and white fuzz on fish.

D.     K. Rhodophyta:  (Red algae or seaweeds)

1.   Most are multicellular and can be large; primarily marine; some are exclusively freshwater inhabitants.  Major photosynthetic pigments, stored in characteristic rhodoplasts, are chlorophyll a and accessory phycobilins; chloroplasts resemble, cyanobacteria.  They lack flagellated sperm; some can photosynthesize at great depths;  Important commercially for sushi, agar, ice cream, toothpaste and cosmetics.

E.      K. Chlorophyta:  Green Algae.  plant kingdom? or the kingdom Viridiplantae. We will include the chlorophyte with the k. Plantae in a later chapter.

1.   range from single cell to multicellular photoautotrphs;  very diverse group;  all have biflagellated stage (usually the gametes); plant–like pigments including chlorophyll a and b;  some have alternating generations; charophytes thought to be the ancestors of green plants

F.      Some additional notable Taxa of protists

1.   P. Actinopoda:  Actinopods are characterized by axopodia or ray feet; planktonic or deep dwelling chemoheterotrophs; Include radiolarians (marine) and heliozoans (freshwater); many have silicate exoskeleton.  This group is probably polyphyletic.

2.   Choanoflagellates:  Single-celled  filtered feeders in aquatic environments.  They are thought to be directly ancestral to sponge choanocytes.

3.      Slime molds:  P. Myxomycota:  Plasmodial slime molds are multinucleate, coenocytic, orange or yellow, ameba-like organisms; Live in moist terrestrial environments and feed primarily on bacteria.  P. Acrasiomycota:  cellular slime molds live as single-celled ameba-like organisms or cellular aggregates.  Feed primarily on bacteria.

4.      Rhizopods:  amoeba-like single-cell organisms with mitochondria.