Superfamilies: Orbitodacea, Spirillinacea, Duostominacea and Robertinacea

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Superfamilies Orbitodacea, Spirillinacea,
Duostominacea and Robertinacea
Lecture 10
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Superfamily Orbitodacea

• The orbitoids are a Late Cretaceous to Miocene
  group of "larger foraminifera" which originated
  in tropical Americas.
• Their tests are radial hyaline and perforate,
  with a discoidal mode of growth, the chambers
  being arranged in annular cycles rather than
  plane spirals.
• A median (equatorial) layer of chambers is
  differentiated from the lateral chambers, seen
  most clearly in axial thin sections
  (Discocyclina).

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Superfamily Spirillinacea

• The wall consists of a single crystal of calcite.
  They are small benthic forms often found adhering
  to algae and other hard substrates.
• Spirillina has a long, planispiral second
  chamber and terminal aperture.
• Patellina has a trochospiral to biserial test in
  which the chambers are subdivided by a
  scroll-like median septum and numerous transverse
  septulae.

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Superfamily Duostominacea

• The Duostominacea are an extinct group that may
  be intermediate in development between certain
  Endothracea and most Rotaliina.
• This is suggested by the wall structure which
  consists of both optically radial and
  microgranular calcite.
• In Duostomina (M. Triassic) the low trochospiral
  test has a basal aperture divided into two by a
  flap.

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Superfamily Robertinacea

• The Robertinacea have optically radial bilamellar
  walls composed of aragonite instead of calcite,
  although this may revert to the latter mineral
  with time in the fossil state.
• The aperture is typically a basal slit extending
  up the face of the last chamber.
• In Robertina the test is high trochospiral, each
  elongate chamber subdivided by transverse
  partitions.
• Ceratobulimina (Upper Cretaceous) has a
  moderately low trochospiral test whilst that of
  Hoeglundina (M. Jurassic-Recent) is provided with
  a keel and peripheral slits marking the primary
  and relict (supplementary) apertures.

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