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Répartition géographique
des Brachiopodes antarctiques

 

| List | Systematics | | BrachNet |       


Brachiopoda in the Antarctic Benthos

by  Christian C. Emig

Directeur de Recherche Honoraire du CNRS

 

This website should be cited as follows:

Emig C. C., 2014. Brachiopoda in the Antarctic benthos. Accessed at http://paleopolis.rediris.es/BrachNet/Antarctic-brachiopoda/index.html on 20xx-xx-xx.


The extant brachiopod taxa are unusual in their relationship to science in that they are studied and described not only by zoologists but also and preponderantly by palaeontologists. Nevertheless most early studies from the Antarctic waters were by zoologists: Friedrich Blochmann (1858-1931), Louis Joubin (1861-1935), Paul Eichler, William Dall (1845-1927), Johann Gerhard Helmcke (1908-), Paul Fischer (1835-1893) who had been sent material garnered during Antarctic cruises. However palaeontologists too: Thomas Davidson (1817-1885), Öhlert (1849-1920), Allan Thomson (1881-1928), Wilfrid Jackson (1880-1978), Merrill Foster (publications in 1974 & 1989) have studied extant Antarctic brachiopods, providing excellent descriptions of the morphology and anatomy of soft body parts.

Palaeontologists who since the 1950’s have described some of the Antarctic brachiopods include only those characteristics found in fossils. Consequently, their accounts are restricted to characters used in describing fossils so the taxonomic characteristics they include are much less complete than the diagnoses prescribed by the International Code of Zoological Nomenclature (ICZN). This failing increased the number of species while omitting well-defined characters proposed previously. New species were established mainly on dimensional and morphological aspects of the shell, so several are invalid taxonomically.

From the 70-75 species described in Antarctic and subAntarctic waters,
there are only 51 valid recognized species, comprising 35 genera [see List]

Genera = 35

Species = 51

Orders = 4

Suborders

Distribution

2

2

Lingulida

 

1

1

Craniida

 

7

8

Rhynchonellida

 

25

40

Terebratulida

of which

g.

sp.

 

9

15

Terebratulidina

16

25

Terebratellidina

The identification of the species living in Antarctica and their geographical distribution, which commonly depasses this polar region, invites comment about the systematics of the brachiopods.


 

A. The successive versions of the ICZN were obviously never applied to brachiopod systematics by palaeontologists. So, as mentioned above, their diagnoses of Antarctic species did not follow the recommendations of the ICZN (2000 http://www.iczn.org/iczn/index.jsp for species, genus or family:

  • Recommendation 13A. Intent to differentiate. When describing a new nominal taxon, an author should make clear his or her purpose to differentiate the taxon by including with it a diagnosis, that is to say, a summary of the characters that differentiate the new nominal taxon from related or similar taxa.

Various examples of diagnoses of Antarctic species considered as valid:

Liothyrella oblonga new species - par Cooper (1973) :
Diagnosis : Elongated Liothyrella with laterally bulging sides, subequal valves, and narrow width, with widest part anterior of the middle.

Aneboconcha new genus - par Cooper (1973, p. 28) :
Diagnosis : Small, smooth, sulcate brachiopods with terebratelliform loop.

et :

Aneboconcha obscura new species - par Cooper (1973, p. 29) :
Diagnosis : Small, oval, sulcate, with terebratelliform loop.

In Brachiopoda systematics these examples are not anecdotal for they are found in recent publications. Such diagnoses do not follow ICZN rules and thus support “splitting”. This practice also occurs at the genus level.

Currently one can read “Diagnosis of genus as for species”. That too is against the rules of the ICZN, because to differentiate genera the generic characteristics must be stated. They cannot be the same as those defining a species.

  • 13.3. Genus-group names. To be available, every new genus-group name published after 1930 (except those proposed for collective groups or ichnotaxa) must, in addition to satisfying the provisions of Article 13.1, be accompanied by the fixation of a type species in the original publication [Art. 68] or be expressly proposed as a new replacement name (nomen novum) [Art. 67.8].

Consequently, a large number of described species, not only those from the Antarctic area, lack phylogenetic authenticity. For example, Liothyrella moseleyi, L. delsolari and L. winteri could be considered synonyms of L. uva, along with Acrobrochus and Liothyrella.


 

B. However, morpho-anatomical characters were brought to prominence by various authors: musculature (Bulmann, 1939; Helmcke, 1939; Foster, 1974; Richardson, 1976), lophophore and disposition of mantle canals (Emig, 1992; Williams et al., 1997), pedicle (Richardson, 1976, 1979), and the taxonomic value of nephridia, gonads and larvae was not yet appreciated. None of these diagnostic characters was used in the revision of systematics in part H (Brachiopoda) of the Treatise of Invertebrate Paleontology (Vol. 2-6), although they are detailed in the Anatomy chapter of Volume 1 (Williams et al., 1997).

Moreover, ignorance regarding ecological data makes it impossible to place a population in its biocenosis. And some of these data may also be considered as having a phylogenetic significance. It is well known that two species of the same genus may not occur in the same biotope. This fact must be taken into account in the Antarctic where specific diversity is low.

Finally, there is a basic need to establish the intra- and inter-population variations for all taxonomic characters, as well as for those that are modified in accordance with the age of the individual. Three or more species of one genus have sometimes been established and described on the basis of differences in a given character, especially those of shell outline and shape. Yet such elements are known to have no taxonomic value.

Consequently there is a pre-eminent need for the establishment of well-defined phylogenetic criteria for each species and genus that will result in a rigorous and reliable systematics, a requirement for any worthwhile analysis of biodiversity and molecular studies. A cladistic approach based on extant brachiopod species cannot be confined solely to the shape and dimensions of the shell.


 

C. The diversity of brachiopods in the Arctic and Antarctic realms is best expressed by their numbers, respectively 10 and 50 species. Obviously the epifauna is more heterogeneous and predominates in the Antarctic communities.

List of brachiopod genera and species in the Arctic (Arndt & Grieg, 1933; Zezina, 1977, 1980, 1997)
and that of the species of the same genera found in the Antarctic:

Genera

Species

Arctic

Antarctic

Pelagodiscus

atlanticus

Discradisca

?

cumingii

Cryptopora

gnomon

Novocrania

anomala

lecointei

Hemithyris

psittacea

 

Terebratulina

retusa

kiiensis

septentrionalis

Liothyrella

delsolari

moseleyi

neozelanica

uva

winteri

Arctosia

arctica

 

Macandrevia

cranium

americana

diamantina

Dallina

septigera

elongata

eltanini

Glaciarcula

spitzbergensis

 

 


 

Already in 1892, Fischer and Öhlert wrote:

« Il sera donc nécessaire désormais de pratiquer une révision nouvelle des Brachiopodes et de supprimer peut-être un certain nombre d’espèces. Il en résulte que plus on étudie ces animaux, plus aussi diminue le chiffre des formes spécifiques légitimes. »

[“At present it will be necessary to do a new revision of the Brachiopods and to perhaps remove a certain number of species. The consequence is that more these animals are studied, more also decreases the number of the valid taxa.”]

 

The correct identification of Brachiopoda is fundamental not only for the assessment of biodiversity, but also in the food and pharmaceutical industries, molecular biology, taphonomy, palaeoecological interpretation, and in the broad field of formal and informal education at all levels.

In the last decades, several important advances have taken place in the way based on new morpho-anatomical taxonomic characters applying also to fossil taxa. Consequently, large revision of the brachiopod genera to ascertain the valid species based on new diagnosis is basically needed, at least in extant taxa.

 

Nota: the citations are available in the page REFERENCES.

Best thanks to my friend Nestor Sander Rotsen for English improvement

Text online since February 19, 2010 - updated on August 18, 2013

 
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