Dictyochaceae
| Dictyochaceae | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name of the order | ||||||||||||
| Dictyochales | ||||||||||||
| Haeckel , 1894 | ||||||||||||
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| Dictyochaceae | ||||||||||||
| Lemmermann , 1901 |
The Dictyochaceae are a family of unicellular, marine algae of the phytoplankton , they are the only family in an order Dictyochales. They are remarkable for their skeleton made of silicon dioxide (as an amorphous opal ), which occurs at least in one stage of life . These skeletons are preserved as fossils in rocks, especially the Neogene , as rock-forming . The group is mostly referred to as Silicoflagellaten , especially by the paleontologists (formerly also formally referred to as the order Silicoflagellata or Silicoflagellida). The group isRecently species-poor, many more species have been described fossil, based on the skeletons. Dictyochaceae are distributed worldwide, they can sometimes reach high densities in seas, especially in the northern latitudes, and cause algal blooms.
description
As far as the life cycle is known, Dictyochaceae occur in three stages: planktonic single cells with a skeleton, naked single cells without a skeleton, and amoeboid, often multinucleated, naked cells that can follow one another within the framework of their life cycle . As far as is known, all stages reproduce asexually; sexual reproduction has not yet been proven.
The cells reach a diameter of about 15 to 20 micrometers. They are mobile by a single flagellum (a drag flagellum ) pointing forward in the swimming direction , which is widened like a wing on one side. The flagellum is covered with tripartite cilia ( Mastigonema ). A second, extremely short flagellum is only visible in the electron microscope, which only occurs on bare cells; only their basal body is present on skeletal cells . In the center of the cell sits the individual nucleus with the neighboring Golgi apparatus . The cell carries relatively small, oval chloroplasts with a pyrenoid (about 30 to 50 per cell in Octasis speculum ) of yellow-green color. In addition to chlorophyll a and chlorophyll c, the carotenoids (from the group of xanthophylls ) fucoxanthin and diadinoxanthin and a few others were observed in low concentrations as pigments . As is typical for the Ochrophyta, every chloroplast is surrounded by four membranes.
The cells are round, but of variable, changeable shape, often with long protruding processes, called tentacles.
The skeleton sits outside the cell and is not covered by the cell membrane; it can be shed from the cell. It consists of a system of interconnected, hollow tubes made of amorphous silicon dioxide. In the basic form, these form two four-, six- or seven-sided rings of different sizes, which are connected by cross struts. Spikes of different sizes protrude outwards from each ring. The result is a flattened, basket-like shape that is star-shaped in plan view. The living cell fills the basket-like structure of the rings more or less completely. The skeleton is doubled, presumably in preparation for cell division.
Fossil forms
Fossil Dictyochaceae are only passed down in the form of their skeletons. The oldest known forms assigned to the group come from the Lower Albium ( Cretaceous Period ). They were found from drill cores from deep-sea sediments in both the Arctic and Antarctic oceans. They were initially rare, but became abruptly more common in arctic latitudes after the santonium . Eight genera have been described from the Cretaceous, of which only one ( Corbisema ) survived the mass extinction on the Cretaceous-Paleogene border . In the Paleogene and early Neogene, Dictyochaceae were quite species-rich and of comparable abundance of forms as the diatoms. Since the early Miocene , their abundance of species has decreased enormously, while the diatoms, which also carry silicate skeletons, have increased significantly. About 250 fossil species have been described.
For pragmatic reasons, the skeletons of Dictyochaceae (usually referred to as silicoflagellates) are usually treated together with the likewise silicate sclerites of Ebriacea and the pentasters, also called sclerites of dinoflagellates , for example of the genus Actiniscus ( Actiniscus pentasterias was originally from Ehrenberg in the genus Dictyocha described).
Biology and way of life
All species are single-celled and part of the marine phytoplankton. They are distributed worldwide, but are more often given from northern latitudes. Algal blooms of the species Octacis speculum (formerly Dictyocha speculum ) from the Baltic Sea have been reported for some years ; these are attributed to increased nutrient levels. On the German coasts, the algal bloom usually consists of bare cells. Although the cells develop pseudopodia- like processes, a purely phototrophic diet is assumed; mixotrophy is unlikely.
Research history
Like many unicellular organisms, it was also unclear for a long time with the Dictyochaceae whether they should be placed in the animal or the plant kingdom (according to the conception at the time). Most of the earlier taxonomists considered the group to be protozoa and accordingly formed the scientific name according to the rules of the zoological code ICZN . Today there is unanimity that they should be treated according to the Botanical Code ( ICN ). As a result, there are several names for many taxa in the older literature. The older name "Silicoflagellaten" is, in the manner of a common name, still in use today and continues to be used, especially in paleontological literature.
Since the group includes small, marine phytoplankton of no economic importance, only a few researchers have dealt with it for a long time. The exception here were the paleontologists, who had found the characteristically shaped skeletons, sometimes en masse, in sedimentary rocks as microfossils. The skeleton was accordingly the structure according to which species ( morpho species ) and genera were described ; most recent forms were also first described after fossil skeletons. This is problematic because the skeletal morphology of the living species has proven to be unexpectedly variable and all species, as far as known, also include forms and stages without a skeleton, some of which can be reproduced in this form in culture over a very long period of time. The status of a number of nominal genera and species is therefore unclear. The variability and abundance of forms is far greater than that of recent forms and encompasses them completely.
The first researcher to describe silicoflagellates was the biologist and geologist Christian Gottfried Ehrenberg in 1837, who noticed fossil forms in a silica slate from Oman, and soon afterwards also in Nordic chalk . Ehrenberg was also the first (in 1840) to find and describe living cells in the Baltic Sea. The scientific name is now attributed to Ernst Haeckel , although he completely misunderstood the shapes and added them to the radiolarians , thus classifying them as "animals". This results from the fact that Eherenberg's name was formed incorrectly under the rules of the ICN.
After the group was widely regarded as " flagellates " (Mastigophora) until the early 1970s , later researchers recognized them as photoautotrophic algae, mostly in an unclear position in the area of the golden brown algae (Chrysophyceae). Molecular methods, especially phylogenomics, made further progress . Then they form together with the Pedinellales (single cells with bare or scaly surface and inner skeleton ( Lorica ), with or without chloroplasts) and the genus Rhizochromulina (amoeboid, naked cells with chloroplasts and flagellated zoospore ) the class of Dictyochophyceae within the Ochrophyta . Although the golden brown algae are quite close relatives of this group, the closest related and sister group were the diatoms or diatoms in the broader sense. The common group is sometimes referred to as the Taxon Diatomista.
Taxonomy and systematics
The taxonomy of the Dictyochaceae is somewhat confused, as numerous species have recently been placed in new genera or traditionally used generic names have been replaced. Apparently there are a number of previously undescribed species. Other species are only known from environmental DNA sequence samples, but the associated organism has not yet been discovered. Only a few species in three genera are known recently.
- Family Dictyochaceae
- Genus Dictyocha Ehrenberg
- Dictyocha fibula Ehrenberg
- Genus Octacis Schiller
- Octacis octonaria Hovasse
- Octacis speculum (Ehrenberg) FH Chang, JM Grieve & JE Sutherland ( synonym Dictyocha speculum , Distephanus speculum )
- Genus Viciticus FHChang
- Vicicitus globosus (Y.Hara & Chihara) FHChang
- Genus Dictyocha Ehrenberg
Literature and Sources
- Robert Edward Lee: Phycology. Cambridge University Press, 2008. ISBN 978-0-521-86408-4 , pp. 360-364.
- Øjvind Moestrup, Helge A, Thomsen: Dictyocha speculum (Silicoflagellata, Dictyochophyceae), studies on armored and unarmored stages. Biologiske Skrifter 37, Copenhagen 1990. ISBN 87-7304-207-2 . 57 pages.
- Kevin McCartney, Jakub Witkowski, David M. Harwood (2014): New Insights into Skeletal Morphology of the Oldest Known Silicoflagellates: Variramus, Cornua and Gleserocha gen. Nov. ANDRILL Research and Publications 60. download
- Zoe V. Finkel (2016): Silicification in the Microalgae. In MA Borowitzka et al. (editors): The Physiology of Microalgae, Developments in Applied Phycology 6: 289-300. doi: 10.1007 / 978-3-319-24945-2 13 .
- Phil Parkinson (2002): Ontogeny v. Phylogeny: The Strange Case of the Silicoflagellates. Constancea 83 (Festschrift Jepsen), article 83.13. download
- Order Dictyochales , in Guiry, MD & Guiry, GM 2019. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. (www.algaebase.org), accessed May 12, 2019.
- Sina M. Adl, Alastair GB Simpson, Christopher E. Lane, Julius Lukeš, David Bass, Samuel S. Bowser, Matthew W. Brown, Fabien Burki, Micah Dunthorn, Vladimir Hampl, Aaron Heiss, Mona Hoppenrath, Enrique Lara, Line le Gall, Denis H. Lynn, Hilary McManus, Edward AD Mitchell, Sharon E. Mozley-Stanridge, Laura W. Parfrey, Jan Pawlowski, Sonja Rueckert, Laura Shadwick, Conrad L. Schoch, Alexey Smirnov, Frederick W. Spiegel: The Revised Classification of Eukaryotes . Journal of Eukaryotic Microbiology 59 (5): 4-119. doi: 10.1111 / j.1550-7408.2012.00644.x (open access)
- Jørgen Kristiansen, Robert A. Andersen: Chrysophytes: Aspects and Problems. Cambridge University Press, 1986. ISBN 978-0-521-32090-0 , Dictyochophyceae, p. 26.
- Noritoshi Suzuki, Masahiro Oba: Oldest Fossil Record of Marine Protists and the Geologic History Towards the Establishment of the Modern-Type Marine Protist World. In: Susumu Ohtsuka, Toshinobu Suzaki, Takeo Horiguchi, Noritoshi Suzuki, Fabrice Not (editors): Marine Protists: Diversity and Dynamics. Springer Verlag, Tokyo etc. 2015, ISBN 978-4-431-55129-4 . Pp. 377-378.
- Helena M. van Tol, Andrew J. Irwin, Zoe V. Finkel (2012): Macroevolutionary trends in silicoflagellate skeletal morphology: the costs and benefits of silicification. Paleobiology, 38 (3): 391-402. doi: 10.1666 / 11022.1 .
- Fook Hoe Chang, Judy Sutherland, Janet Bradford ‐ Grieve (2017): Taxonomic revision of Dictyochales (Dictyochophyceae) based on morphological, ultrastructural, biochemical and molecular data. Phycological Reseaerch 65 (3): 235-247. doi: 10.1111 / pre.12181 .
- N. Daugbjerg, P. Henriksen (2001): Pigment Composition and rbcL Sequence Data from the Silicoflagellate Dictyocha speculum: a Heterokont Alga with Pigments Similar to some Haptophytes. Journal of Phycology 37: 1110-1120. doi: 10.1046 / j.1529-8817.2001.01061.x .