Lorica (single cell)

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A Lorica designated (at unicellular protists : ciliates and flagellates ) a form of extracellular envelope around the cell (or a rare cell colony ) enclosing this. A Lorica has an opening at one end, sometimes at both, it can either be anchored to the substrate with a stalk region or be carried along by the freely swimming organism. Cell envelopes known as Lorica can consist of organic material (as a basic component carbohydrates or proteins ), made up of separated mineral components such as calcium carbonate or silicon dioxide , or mineral components (such as iron oxides, grains of sand, organic detritus or others) can be incorporated into an organic (often mucous ) matrix ) be stored. The various structures designated as Lorica are neither homologous in their formation nor in their shape , the term merely reflects a certain morphological similarity. Cell envelopes known as Lorica are alternatively referred to with numerous other expressions such as housing or sheath. Many researchers combine all forms of extracellular envelopes, including the various forms of a Lorica, to form a "Type III".

Lorica the frilled flagellates

The collar flagellates (Choanomonada or Choanoflagellata) of the order Acanthoecida are characterized by a Lorica, while the second order Craspedida have a differently structured envelope structure called theca . The lorica of the Acanthoecida consists of individual strips, known as costae (ribs), mainly made up of silicon dioxide, which form a basket-like covering around the cell. The costae can protrude more or less. Usually this basket consists of two layers, one layer of costae arranged lengthways and one layer of costae arranged transversely or helically, which connects them. The costae, which are arranged transversely, are usually on the inside, but can also follow the lengthways arranged on the outside in individual taxa. The inner surface of the inner costae, towards the cell, has a thin covering of fibers (microfibils) made from carbohydrates. Each individual costa is composed of rod-shaped fiber elements that are stacked against each other in opposite directions, their number can vary depending on the type from 5 to several hundred per costa. These are produced intracellularly, put together and then deposited on the outside. The Lorica is usually only a few micrometers long, with Bicosta spinifera ( Acanthoecidae , Choanoflagellida ) it reaches 100 micrometers in length. The individual costae are usually structured in the same way, with a few groups two or more different types are morphologically distinguishable. They are either flattened or have a round cross-section. Two different variants are possible for cell division. In a few genera (e.g. Acanthoeca ) one daughter cell inherits the Lorica, the other, non-enveloped (nudiform) swims away and later develops its own Lorica. In other genera, a (tectiform) daughter cell is pushed out of the old Lorica in the opposite direction and already forms a new shell of costae that were prefabricated before cell division.

Lorica of the Ciliates

In the Ciliophora , the structure and shape of the Lorica is more variable. Mostly it is a more or less loose shell that is anchored to the substrate and has an opening at the front (anterior) end. In some groups, the cells with their Loricae form a tree-like cell colony. The Lorica is separated from the organism and reinforced in different groups with foreign material coming from outside. Their matrix can be made up of fibrous proteins; slimy coats made of mucopolysaccharides are more common. They can contain chitin , tectin or pseudochitin. The shell is sometimes calcified, or grains of sand or other foreign materials are embedded. A Lorica occurs in ciliates of the subclass Peritrichia in the families Lagenophryidae and Vaginicolidae or in the Folliculinidae belonging to the Heterotrichida . In the case of the vaginicoid, it can be provided with a lid (operculum).

Ciliates of the suborder Tintinnina of the Tintinniden also have a Lorica, although they are free-swimming organisms of the microzooplankton. Many genera such as Tintinnopsis can be determined based on the shape of the Lorica. This is usually tubular or vase-shaped. The Lorica is a protection against predators in these organisms, it has been shown that individuals with a large Lorica are less likely to be eaten by copepods.

Individual evidence

  1. ^ HR Preisig, OR Anderson, JO Corliss, Ø. Meestrup, MJ Powell, RW Robertson, R. Wetherbee (1994): Terminology and nomenclature of protist cell surface structures. Protoplasm 181: 1-28.
  2. ^ Burkhard Becker: The cell surface of flagellates. In Barry SCLeadbeater & JCGreen (editors): The Flagellates, Unity, diversity and evolution. Taylor & Francis, London and New York 2000. ISBN 0-7484-0914-9 .
  3. ↑ Barry SC Leadbeater: The Choanoflagellates, Evolution, Biology and Ecology. Cambridge University Press, 2015. 350 pages. ISBN 978-0-521-88444-0 .
  4. ^ HR Preisig (1994): Siliceous structures and silicification in flagellated protists. In R. Wetherbee, RA Andersen, JD Pickett-Heaps (edtors): The Protistan Cell Surface. Springer Verlag, Vienna & New York 1994. ISBN 978-3-7091-9380-8 .
  5. ↑ Illustrations of different species with their Lorica z. B. in Helge Abildhauge Thomsen & Jette Buch Østergaard (2017): Acanthoecid choanoflagellates from the Atlantic Arctic Region - a baseline study. Heliyon 3 (7): e00345. doi: 10.1016 / j.heliyon.2017.e00345
  6. ^ John O. Corliss: The ciliated Protozoa. Characterization, Classification and Guide to the Literature. Pergamon Press, Oxford etc., 2nd edition 1979. ISBN 0-08-018752-8
  7. ^ John Dolan (2010): Morphology and Ecology in Tintinnid Ciliates of the Marine Plankton: Correlates of Lorica Dimensions. Acta Protozoologica 49: 235-244.