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Alegret, Ortiz & Kaminski (eds.), 2012. Ninth International Workshop on Agglutinated Foraminifera, Abstract Volume
Foraminiferal design: Morphogenesis of agglutinated chambers
Jarosław TYSZKA
Institute of Geological Sciences, Polish Academy of Sciences, Kraków Research Centre, BioGeoLab,
Senacka 1, 31-002 Kraków, Poland.
e-mail: ndtyszka@cyf-kr.edu.pl
Charles Darwin wrote to William Benjamin Carpenter in 1872 “The case of the three species
of protozoan (I forget the names) which apparently select differently sized grains of sand, etc.,
is almost the most wonderful fact I ever heard of. One cannot believe that they have mental
power enough to do so, and how any structure or kind of viscidity can lead to this result
passes all understanding.” We are still amazed like Darwin was how foraminifera selct grains
and construct their shells. What do we know about it in 2012? Do we understand more?
We do know that agglutinated foraminifera as “unicellular organisms are superb
builders of their houses, possessing the know-how to build using naturally occurring ‘bricks’
and ‘cements’ with enviable skill” (Ehrlich, 2010). Foraminifera are excellent architects
implementing their shell designs by iterative growth of chambers with skills inherited from
generation to generation. The problem is that it is still not clear how they do it.
A considerable progress in phylogenetic studies may direct us toward better
understanding of evolutionary and morphogenetic relationships in Foraminifera. Recent
molecular phylogenetic studies have shown that agglutinated foraminifera should not be
treated as a monophyletic group any more (e.g., Pawlowski et al., 2003). It further means that
the higher rank classification, presented by Loeblich and Tappan (1987, 1992), separating the
foraminiferal orders based upon their shell composition, mineralogy and structure cannot be
applied. Gross test morphology is a better approach for higher groups of foraminifera (e.g.
Mikhalevich, 1998, 2000; Mikhalevich & Debenay, 2001).
It simply means that a test or shell design is more important than a fabric of its wall.
Actually, in polythalamous foraminifera, the most characteristic feature is an overall chamber
shape, which includes either tubular or globular forms. The same pattern of chamber shapes is
observed both in agglutinated and calcareous foraminifera that implicates their similar
evolutionary and morphogenetic origin. This conclusion comes from molecular phylogenetics
(e.g., Pawlowski et al., 2003; Groussin et al., 2011) and from theoretical morphogenetic
studies (Tyszka and Topa, 2005, 2007; Tyszka, 2006). If the same patterns of chamber
morphologies are shared in agglutinated and calcareous foraminifera and both groups are
phylogenetically relatively closely related, it might be assumed that both of them use similar
morphogenetic structures and chamber formation strategies to achieve similar constructional
results.
Most similar are bilocular or multilocular tubular foraminifera, including such groups
like porcelanous miliolids, agglutinated rzehakinids and ammodiscids. All of them agglutinate
their tubular chambers, but porcelanous foraminifera agglutinate their wall from internally
secreted grains formed in vesicles as high Mg-calcite microneedles. In contrast, true
agglutinated foraminifera construct their walls from foreign, external grains collected nearby.
An overall shape of chambers is probably designed by dense anastomosing networks of
microtubules covering organic templates with permanently open apertures during the chamber
formation. Globular chambers are distinctly different because they are formed on a closed
balloon-like, elastic structure, which is a template for a final chamber. Apertures in such
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