The Living Foraminifera

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Lecture 3
The Living Foraminifera
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The Living Foraminifera

• The micropaleontology is concerned with the dead
  shells of foraminifera and classification of
  fossil species proceeds upon the morphology of
  the hard parts or test.

• Foraminifera are single-celled animals (phylum
  Protozoa) and belong to the same class Rhizopoda
  distinguished by temporary extrusions of the
  protoplasm or pseudopodia.
• Foraminifera differ from Amoeba in that the
  pseudopods are fine and hair-like together to
  form a spreading, reticulate network, as well as
  in agglutinated or calcareous test.

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Orbulina universa, a sand sized single
chambered test surrounded by delicate spines
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• The most primitive order, the Allogromida, the
  test is an organic, gelatinous sac-like
  structure, 1-10 µm thick, composed of
  glycoprotein and referred to as tectin.
• It is an internal structure surrounded by
  ectoplasm immediately external to the primary
  cell membrane which contains the dense so-like
  endoplasm.
• In advanced foraminifera such as the
  globigerinids, the organic layer becomes an inner
  lining to the calcareous test.
• Most structures occur in the endoplasm.
• The overall organization of the cell is
  controlled by the nucleus.

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NUTRITION

• The food of foraminifera includes
• unicellular algae, especially diatoms,
• other protozoans and
• small metazoans including crustaceans such as
  copepods.
• Solid food may be carried through the aperture
  and digested with the help of enzymes secreted by
  the lysosomes or partly digested in place.

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REPRODUCTION

• A life cycle is termed heterophasic when it
  characteristically contains two different phases,
  or types of reproduction and maturation.
• Among some foraminifera there is this same
  alternation of an asexual followed by a sexual
  generation.
• The benthic genus Rosalina, reproduce only
  asexual in culture.
• The young gamonts with the larger proloculus are
  termed the megalospheric generation, while the
  individuals with smaller proloculi are called the
  microspheric generation.
• Thus the two morphologically distinct tests are
  termed dimorphism.

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• Dimorphic pairs are found among smaller and
  larger benthic foraminifera, but have not been
  recognized in planktonic genera.
• The microspheric generation with the smaller
  proloculus is termed B form, whereas the
  megalospheric phase (with larger proloculus) is
  called the A form.
• There are genera (Cibicides, Triloculina and
  Elphidium) in which a third generation commonly
  occurs, which is called A1, the second
  megalospheric generation.

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• The protoplasm of a foraminiferid comprises a
  single cell differentiated into an outer layer of
  clear ectoplasm and an inner layer of darker,
  coloured endoplasm.
• The ectoplasm surrounds the test and gives rise
  to numerous thread-like (filose) or branching
  (reticulose) pseudopodia along which the food
  material is drawn and the debris expelled.

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• The complete cycle for Elphidium crispum takes
  two years in the shallower parts of the English
  Channel, although it may be delayed at deeper
  stations.
• Asexual reproduction reaches a peak in April.
• All the protoplasm leaves the test and chambers
  are added at the rate of about two per day.
• Sexual reproduction begins early in the second
  spring as temperatures begin to rise.
• The gametes conjugate outside in open sea to
  produce zygotes and the B form then develops and
  matures during the second summer.

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Life cycle of Elphidium crispum (duration 2 years)
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