1. Introduction
    1. Also called the Prymnesiophyceae, or coccolithophorads
      1. Coccolithophorad refers to their calcareous scales, called coccoliths, which are important stratigraphic markers
    2. Marine unicellular flagellates
      1. Zoids (flagellate cells) with wo naked flagella and a haptonema
    3. Pigmentation is similar to that seen in some heterokont groups, but plastids seem to have been acquired independently
    4. Major players in global phytoplankton, particularly in the open ocean
    5. Can be bloom formers
  2. Structure & metabolism
    1. Typically flagellates
      1. Two naked flagella, which may be equal or unequal in length
        1. One order, the Pavlovales has delicate hairs (not mastigonemes) on the flagella
        2. Unlike heterokonts, do not have swelling at flagellar base
      2. Haptonema is present in most
        1. A long, thin structure reminiscent of a flagellum, but with a different ultrastructure
        2. 6-7 microtubules in a ring or crescent, with a fold of endoplasmic reticulum extending out within the flagellum
        3. In cross section a small number of individual microtubules and three membrane layers are seen
        4. Contrast this with the typical eukaryotic 9+2 flagellum, where each of the 9 flagellar rods is composed of three fused microtubules
    2. Sometimes with amoeboid, coccoid, palmelloid, or filamentous stages
    3. Cell surface is typically covered with external scales, often of more than one type
      1. Tiny cellulosic scales
      2. Calcified scales -- Coccoliths
        1. These can be large, and may be visible with the light microscope
        2. Coccoliths fossilize well, and are important stratigraphic markers.
        3. The chalk deposits from the Cretaceous are composed largely of coccoliths
        4. Coccoliths were known from the fossil record before the living organsims that produce them were identified.
      3. Scales are synthesized in the ER, then transported to the surface of the cell
      4. A few species lack scales
    4. Mitosis - distinctive
      1. Open
      2. Chromatin plate with channels for pole-to-pole microtubules
    5. Chloroplast is secondary, with a CER, but no nucleomorph
      1. Thylakoids are stacked in threes
      2. There are no girdle lamellae
      3. There may be an eyespot in the chloroplast, but there is no associated flagellar swelling
    6. Mitochondrial genetic code uses UGA for tryptophan
  3. Reproduction
    1. Some have a heteromorphic alternation of generations
    2. Diploid flagellate alternates with haploid filament
    3. Life cycle of others is unclear
  4. Classification
    1. About 75 genera & 500 species
    2. Once classified with the heterokonts on the basis of pigmentation, haptophytes are now thought to have acquired their secondary plastid independent of heterokonts.
      1. Haptophytes and heterokonts together all called chromophytes (a reference to their golden pigmentation)
      2. Text p. 223 has a good summary of the characters separating haptophytes from heterokonts:
        1. Lack of pleuronematic flagella with mastigonemes
        2. Presence of haptonema
        3. Lack of chloroplast girdle lamellae
        4. Distinct structure of golgi apparatus
        5. Absence of flagellar swelling
        6. Presence of peripheral ER cisternae beneath plasmalemma
        7. Arrangement of chloroplast DNA
        8. Distinctive pattern of mitosis
    3. Pavlovales are probably the outgroup to the rest of the Haptophyta
      1. Pavlova gyrans
        1. Strongly metabolic, with the cell shape highly variable, it is named for a Russian ballerina Anna Pavlova
    4. Prymnesiales
      1. Chrysochromulina
    5. Isochrysidales
      1. Isochrisis
    6. Coccolithophorales
      1. Emiliana huxleyi - global distribution, bloom former, major player in marine phytoplankton
      2. Thought to be largest global producer of calcium carbonate, hence major sink for CO2.
  5. Ecology
    1. Mostly marine, a few are freshwater
    2. From tropics to polar waters. Greatest diversity is in the tropics
    3. Major contributors to primary productivity in open ocean
    4. May form massive blooms
      1. Because the coccoliths reflect light, these are called "whitewater blooms"
      2. Most haptophytes are nontoxic, and are considered to have a high food value (for zooplankton) and to be major contributors to marine food web
      3. However, a major bloom of Chrysochromulina polylepis near Sweden and Norway was toxic, and had a substantial environmental and economic impact.
  6. Economic Importance
    1. Form the basis for key marine food webs
    2. Ultimately responsible for some major oil deposits
    3. Key role in global CO2 balance
    4. Formed cretaceous chalk beds
    5. Blooms may be toxic

Required Reading: VdH Chapter 14

Supplementary Reading:

Daugbjerg, N., and R.A. Andersen. 1997. Phylogenetic analysis of the rbcL sequences from haptophytes and heterokont algae suggest their chloroplasts are unrelated. Mol. Biol. Evol. 14:1242-1251.