Botanical affinities of Leiospheres

24 July, 2009

 

Leiospheres have generally been considered as resting cysts and their aperture (pylome) has been interpreted as an excystment opening. However, they may also represent vegetative stages of the algal life cycle, as in modern acid resistant microalgae apertures similar to pylomes may develop also in vegetative stages, e.g. as flagellar pores.

There may be no possibility of discriminating between vegetative and resting stages (cysts) in fossil material. The acid resistance and the possibility to be fossilized are widespread in the algae and occur variably in all their life stages, in vegetative cells and also in resting cysts.

 

Apertures

Apertures have a restricted taxonomic significance and they are not useful for the determination of life stages. Vegetative stages of algae and also encysted resting stages are likely to be preserved as fossils. Apertures on vegetative cells, however, cannot always be definitely discriminated from excystment openings. The pylome may be a flagellar pore similar to that of certain modern algae (e.g. Trachelomonas, see below).

If the fossils are of flagellate affinity, every one should have an aperture in its vegetative stage. Forms without apertures may be cysts of the same or different species, but also vegetative stages of unflagelled taxa. When the aperture is an excystment feature, it is present only during one life stage. Cells without apertures then may be closed cysts, but also vegetative stages of other than flagellate affinity. Cells with apertures may be mature cysts, but also vegetative stages of flagellate affinity.

In the original diagnosis of Leiosphaeridia (Eisenack 1958) pylome (aperture) is said to be present. In the following original description is remarked that pylomes are common in some species but rare or absent in others. This variation is proposed to be depending either on specific characters or on the stage of the life cycle of the organisms at the time when they were buried. Microfossils with pylomes were interpreted as obviously abandoned cells in their final life stage, and the function of the opening, was without doubts considered to be making it possible for the protoplast to extrude. Consequently pylomes are not necessarily present on every fossil specimen of a taxon, and their occurrence has no taxonomic value. Only their structure may be a feature important for the classification, possibly limited to the rank of species.

In some taxa a pylome is always present, in others pylomes are never or only occasionally observed with certainty. In “thousands of specimens” of the original material of Leiosphaeridia plicata and L. ralla there was no pylome (Felix 1965), and in 3324 specimens of L. wenlockia there were “one or two” with pylome (Downie 1959).

Generally, leiospheres have been considered as cysts having pylomes and ruptures as excystment features. However, since excystment is a genetically controlled characteristic process that is constant within a taxon, pylomes and ruptures cannot exist both as excystment features in the same species.

 

Environmental modifications

In the fossil record most often it is impossible to elucidate if variability is due to environmentally controlled factors or to different stages of the algal life cycle. Thus, different fossil genera from distant deposits may be only modifications of the same natural species.

Cells that do not differentiate hard parts do not always obtain identical morphological features when they are developed separately in different environments. Except this environmentally controlled morphogenesis the different life stages of the algal cell may generate morphologic variability. Further, in restricted environments disastrous events may occur which may often generate radical changes in the metabolism and morphological appearance of the cells.

A satisfactory classification of modern algae must pay sufficient attention to the morphological variability and life history of each taxon. Many species first described on the basis of specimens representing only one stage of their life cycles were later defined as life stages of other species.

 

Coenobia

I have identified fossil algal coenobia in a sample from the Upper Riphean Mirojedikha Beds in the Turukhansk region, eastern Siberia. The fossils I investigated derive from the Mirojedikha River and were extracted from a sample from the Upper Riphean Mirojedikha Beds.

The Mirojedikha Beds are about 200 m thick shallow water sediments consisting of dolostones, limestones, and shales. The present sample was collected in l967 by my friend, the Late Professor Boris V. Timofeev at the type locality at the Mirojedikha River, four kilometers from its confluence with the Yenisey River, 30 kilometers north of the town of Turukhansk. The sample is a dark-grey, clayey shale which derives from the lower part of the Mirojedikha Beds.

Vesicles of coenobia and solitary leiospheres do not display morphologic differences. The dimensions of vesicles of coenobia correspond to those of larger specimens in the bimodal size distribution of solitary leiospheres from the same sample.

Algal coenobia are sparsely reported as fossil findings. From the Cretaceous-Tertiary they are described as the genus Palambages. The first findings of coenobia in the Palaeozoic were reported from the Silurian of Libya in 1962. There were not any records from the Precambrian until my findings in 1982.

Faulty or rough processing may be the reason for the scantiness of reports of fossil colonies. Maybe most samples yield colonies rather than single specimens if they are treated with gentle care. Clusters, flakes, and different kinds of agglomerations of uniform fossil microalgae have been reported as colonies though they do not strictly represent colonies.

A coenobium is a definitely integrated colony composed of a certain number of cells which are determined during its early development; after the embryonic phase cell-division does not occur until the following reproductive phase. In coenobia the joints and sheaths are usually resistant and likely to be preserved as fossils. However, unicell production and colony formation are influenced by environmentaly controlled factors.

In the algae there is a parallel development from simple to more elaborate forms so that practically all types of cellular and colonial organizations have their counterparts in different classes. The characters necessary for discrimination between classes are not preserved as fossils. Consequently, relating fossil coenobia to modern algal taxa is impossible.

I referred both coenobial and solitary forms to a species with the new combination name Leiosphaeridia asperata (Naumova) Lindgren. Kildinella hyperboreica is not the correct name of this taxon. Protoleiosphaeridium, Kildinella, and Polyedrosphaeridium are congeneric with Leiosphaeridia, as well as the not validly published genera Leiopsophosphaera, Macroptycha, and Scaphita.

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Morphology and taxonomy
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Diagnostic features in modern algae
Morphometry of modern and fossil algae
Genus Leiosphaeridia
Distribution of Leiosphaeridia

References

Downie, C., 1959.
Hystrichospheresfrom the Silurian Wenlock Shale of England. Paleontology, 2: 26—71. London.
Eisenack, A., 1958.
Tasmanites Newton 1875 und Leiosphaeridia n.g. als Gattungen der Hystrichosphaeridea. Palaeontographica Abt.A, 110: 1—19. Stuttgart.
Felix, C.J., 1965.
Neogene Tasmanites and leiosphere from southern Louisiana, U.S.A Palaeontology, 8: 16—26. London.
Lindgren, S., 1981.
Remarks on the taxonomy, botanical affinities, and distribution of leiospheres. (Summary in Russian) Stockholm Contrib. Geol., 38(1): 1—20. Stockholm. ISBN 91-22-00500-5. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
Taxonomic review of Leiosphaeridia from the Mesozoic and Tertiary. Stockholm Contrib. Geol., 38 (2): 21—33. Stockholm. ISBN 91-22-00502-1. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
Algal coenobia and leiospheres from the Upper Riphean of the Turukhansk region, eastern Siberia. Stockholm Contrib. Geol., 38 (3): 35—45. Stockholm. ISBN 91-22-00504-8. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 37 (11): 139—143. Stockholm. ISBN 91-22-00487-4. ISSN 0585-3532.
Lindgren, S., 1984.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 39 (5): 139—144. Stockholm. ISBN 91-22-00517-x. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.


Genus Leiosphaeridia

24 July, 2009

 

The taxonomic classification of spherical microalgae is very complex, since:

  • it is impossible to refer these forms to modern algal taxa because of the lack of relevant characters for classification
  • vegetative cells and resting stages (cysts) cannot be discriminated with respect to only fossilized parts;
  • cell shape and ornamentation may vary between different stages of the algal life cycle and can be modificatively affected by environmental factors, such as nutrition and temperature
  • excystment features (pylomes, ruptures) are not constant in the algal life cycle, and excystment apertures (pylomes) cannot be discriminated always with certainty from apertures in vegetative stages, e.g. flagellar pores.

Leiosphaeridia (Eisenack 1958) comprises acid resistant, spherical to ovoidal microfossils without processes, without divisions into fields, and without traverse and longitudinal furrows or girdles. The cell wall is thin and without tubes, the surface is smooth or with slight ornamentation. An aperture (pylome) may be present, and has been considered as an excystment mechanism. Other methods of dehiscence are also recorded, e.g. by a split.

The original diagnosis by Eisenack in 1958 was slightly emended by Downie and Sarjeant in 1963 to include slight ornamentation and to exclude reference to colour. However, the view on color was taken earlier, and published by Eisenack in 1962.

Leiosphaeridia was established to accommodate leiospheres not attributable to Tasmanites (Newton 1875) because the nomenclatural type of Leiosphaera—a genus introduced by Eisenack in 1938—proved to be conspecific with a species of Tasmanites.

 

Synonymy

  • Kildinella, Lophosphaeridium, and Protoleiosphaeridium do not display any differences from the diagnosis of Leiosphaeridia. Also Leiopsophosphaera and Uniporata seem to be congeneric with Leiosphaeridia.
  • Leiosphaeridium is an illegitimate name. Macroptycha and Scaphita are not validly published.
  • Campenia and Lancettopsis may be congeneric with Leiosphaeridia, but are not examined.

Kildinella (Shepeleva & Timofeev ex Timofeev) comprises according to the protologue smooth or shagreen spherical microfossils, ranging from 15 to 70 µm in diameter, with clearly delimited folds. They differed from Leiosphaeridia specimens only in being smaller and having denser membranes.

The folds evidently were generated by compression and the restricted size range is of no taxonomic value. When I examined the original material of Kildinella, I could not find any distinct features different from the diagnosis of Leiosphaeridia.

Kildinella was established by Shepeleva & Timofeev in 1963, but no species was described and no nomenclatural type was indicated. Thus the name was not validly published until Timofeev in 1966 described Kildinella hyperboreica and designated it as the type species.

Only a few species of Kildinella have been described. My friend, the Late Professor Boris V. Timofeev showed to me in Leningrad 1979 that they are essential parts of biostratigraphically useful microalgal assemblages identified in the pre-Cambrian of the Soviet Union.

Lophosphaeridium (Timofeev ex Downie) differs from Leiosphaeridia only in having a tuberculose ornamental sculpture. The difference is diffuse and a more or less developed ornamentation is the only feature for the generic classification. When I examined the original material of Lophosphaeridium, I could not find any distinct features different from the diagnosis of Leiosphaeridia. However, I regarded more extensive analyses required for establishing the taxonomic relations.

Lophosphaeridium was introduced by Timofeev in 1959 but as no type species was selected it was not valid until Downie designated the nomenclatural type in 1963.

Protoleiosphaeridium comprises small leiospheres (less than 50 µm in diameter) with smooth or shagreen surface, and ranges completely within the diagnosis of Leiosphaeridia. This genus was established by Timofeev in 1959, and became valid by designation of a lectotype in 1960. The circumscription of the genus was slightly expanded by Staplin in 1961 as to include all types of minor overall ornamentation. Leiosphaeridia and Protoleiosphaeridium were treated as congeneric by Downie & Sarjeant in 1963.

Leiopsophosphaera (Naumova) comprises large cells with smooth or shagreen, pitted surface. Dr Pykhova told me in 1978 that Leiopsophosphaera differs from Leiosphaeridia and Uniporata only in the sculptural ornamentation. This Proterozoic and Palaeozoic genus seems to range within the diagnosis of Leiosphaeridia.

A more detailed investigation of the taxonomy should indude a close examination of the original material if it is preserved. Studying that material was not possible for me, nor was I able to find Naumova’s paper from 1960 with the original diagnosis. Leiopsophosphaera and Leiosphaeridia were treated as congeneric by Yin & Li in 1978.

Uniporata (Naumova in Pykhova) comprises cells with ornamented surface and a large pylome. Dr Pykhova told me in 1978 that Uniporata differs from Leiosphaeridia only in having a large pylome. The type species indicated in the protologue of Uniporata is a nomen nudum and thus the name is not validly published.

The Proterozoic and Palaeozoic genus Uniporata was established by Naumova in Pykhova 1969. It seems to range within the diagnosis of Leiosphaeridia. A more detailed investigation of the taxonomy should indude a close examination of the original material if it is preserved. Studying that material was not possible for me.

Leiosphaeridium was proposed by Timofeev in 1959 as an amendment of Eisenack’s Leiosphaera. The original spelling of a name is to be retained and Leiosphaeridium is not to be considered an orthographic variant of Leiosphaera. As the name is nomenclaturally superfluous, it is illegitimate.

Staplin emended Timofeev’s diagnosis of Leiosphaeridium and regarded the name “as a new generic taxon” with L. eisenackii (Timofeev) as a new type species. Based on a different type the name is a later homonym and thus illegitimate.

The transference to Leiosphaeridia of Leiosphaeridium eisenackii made by Downie & Sarjeant in 1963 is not valid since it is done without clear references to the basionym.

Macroptycha and Scaphita are names used by Timofeev in 1973 for boat-shaped forms with large longitudinal folds or without folds, respectively. However, both names were not validly published. The folds were interpreted as prolonged chambers, but evidently represent compressional features. Before 1973 forms identical with Macroptycha and Scaphita were referred to Leiosphaeridia by Timofeev and others.

Campenia, described by Mädler in 1963, differs from Leiosphaeridia in possessing an elliptical slit that is supposed to be homologous with the pylome. The diagnosis of Leiosphaeridia, however, does not exclude opening by a slit. Lancettopsis—also described by Mädler in 1963—comprises folded and rolled up vesicles similar to Scaphita. Analyses of the original material is required for establishing the taxonomic relations.

 

Complex classification

To illustrate the complex leiosphere classification two species may be mentioned.

Protoleiosphaeridium papillatum was described by Staplin in 1961. Two years later—in 1963—it was transferred (but not validly) to Leiosphaeridia by Downie & Sarjeant, and further five years later—in 1968—to Lophosphaeridium by Martin.

Protoleiosphaeridium granulosum was also introduced by Staplin in 1961. It was in 1963 transferred by Downie & Sarjeant to Leiosphaeridia, and in the same year by the same Downie (without Sarjeant as coauthor) to Lophosphaeridium. Both these transferences are, however, contrary to the nomenclatural rules, and the valid publication of the name Leiosphaeridia granulosa was made by Pocock in 1972—but for a different taxon!

 

New species

I have described two new species of acid resistant spherical microalgae, referable to genus Leiosphaeridia, from the Upper Cretaceous of the province Scania (Skåne), southern Sweden.

Leiosphaeridia nelliae Lindgren 1982c is described from a Cenomanian clay deposit penetrated by a boring at Åhus in the Kristianstad area. This species is diagnosed by its small size and the lack of apertures or any obvious dehiscence mechanism. It resembles some Palaeozoic species, but all Mesozoic species with similar appearance are much larger.

Leiosphaeridia scanica Lindgren 1984 is described from the Campanian and Maastrichtian penetrated by a boring at Trelleborg. This species differs from other species of Leiosphaeridia in having a smooth vesicle and a constantly present pylome.

Leiosphaeridia asperata (Naumova) Lindgren is a new combination I established in my 1982b paper with Trachytriletus asperatus Naumova as basionym.

BACK TO


Morphology and taxonomy
Botanical affinities
Diagnostic features in modern algae
Morphometry of modern and fossil algae
  FORWARD TO


Distribution of Leiosphaeridia

References

Eisenack, A., 1958.
Tasmanites Newton 1875 und Leiosphaeridia n.g. als Gattungen der Hystrichosphaeridea. Palaeontographica Abt. A, 110: 1—19. Stuttgart.
Eisenack, A., 1962.
Einigen Bemerkungen zu neueren Arbeiten uber Hystrichosphären. Neues Jb. Geol. Paläont. Mh., 102: 92—101. Stuttgart.
Downie,C. & Sarjeant, W.A.S., 1963.
On the interpretatio and status of some hystrichospher genera. Palaeontology, 6: 83—96. London.
Lindgren, S., 1981.
Remarks on the taxonomy, botanical affinities, and distribution of leiospheres. (Summary in Russian) Stockholm Contrib. Geol., 38(1): 1—20. Stockholm. ISBN 91-22-00500-5. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982a.
Taxonomic review of Leiosphaeridia from the Mesozoic and Tertiary. Stockholm Contrib. Geol., 38 (2): 21—33. Stockholm. ISBN 91-22-00502-1. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982b.
Algal coenobia and leiospheres from the Upper Riphean of the Turukhansk region, eastern Siberia. Stockholm Contrib. Geol., 38 (3): 35—45. Stockholm. ISBN 91-22-00504-8. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982c.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 37 (11): 139—143. Stockholm. ISBN 91-22-00487-4. ISSN 0585-3532.
Lindgren, S., 1984.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 39 (5): 139—144. Stockholm. ISBN 91-22-00517-x. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.