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clade I araphid pennate diatoms

David G. Mann
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Asterionellopsis valveDimeregramma: dividing frustuleRhaphoneis valve
taxon links [up-->]Rhaphoneidaceae [up-->]Plagiogrammaceae [down<--]Bacillariophyceae Interpreting the tree
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Containing group: Bacillariophyceae

Introduction

These diatoms were never grouped together previously, in classifications based on morphology, but in molecular phylogenies (e.g. Kooistra et al. 2004, 2006, Medlin & Kaczmarska 2004, Sorhannus 2007) they consistently appear as a monophyletic group, although very few species have yet been grown and sequenced. No morphological synapomorphies have been identified for the group and there may be none. However, the cytological characteristics of most members have not been recorded and absolutely nothing is known about the reproductive biology of clade I araphid pennates, which is particularly unfortunate because it is conceivable that they might provide the key to understanding how the oogamy of centric diatoms was replaced by isogamy (rarely anisogamy).

All species known to belong to clade I araphid pennates are marine. The Plagiogrammaceae and Rhaphoneidaceae grow attached to rocks, sand grains and seaweeds (though like other benthic marine species, they are sometimes swept up into coastal plankton), living as solitary cells or forming chains or clusters. The exception is Neodelphineis, which is habitually planktonic and grows in zig-zag colonies (Round et al. 1990). Asterionellopsis and Asteroplanus are are both planktonic, forming helical or stellate colonies.

Clade I is discussed by Kooistra et al. (2004, 2006).

Clade I araphid pennates are apparently the first pennate diatoms to appear in the fossil record although, because the clade is characterized by molecular genetic data, any statements about its fossil record are rather speculative.

Characteristics

Clade I is based solely on molecular evidence (principally from SSU rDNA). No morphological synapomorphies have been identified. None of the features mentioned below is restricted to clade I araphids, and none is possessed by all clade II taxa.

References

Kooistra, W.H.C.F., Forlani, G., Sterrenburg, F.A.S. & De Stefano, M. (2004). Molecular phylogeny and morphology of the marine diatom Talaroneis posidoniae gen. et sp. nov. (Bacillariophyta) advocate the return of the Plagiogrammaceae to the pennate diatoms. Phycologia 43: 58-67.

Kooistra, W.C.H.F., Chepurnov, V., Medlin, L.K., De Stefano, M., Sabbe, K. & Mann, D.G. (2006). Evolution of the diatoms. In: Plant Genome: Biodiversity and Evolution. Vol. 2B: Lower Groups (Ed. by A.K. Sharma & A. Sharma), pp. 117-178. Oxford & IBH Publishing, New Delhi , India and Science Publishers, USA.

Medlin, L.K. & Kaczmarska, I. (2004). Evolution of the diatoms: V. Morphological and cytological support for the major clades and a taxonomic revision. Phycologia 43: 245270.

Round, F.E., Crawford, R.M. & Mann, D.G. (1990). The diatoms. Biology and morphology of the genera. Cambridge University Press, Cambridge. 747 pp.

Sims, P.A., Mann, D.G. & Medlin, L.K. (2006). Evolution of the diatoms: insights from fossil, biological and molecular data. Phycologia 45: 361-402.

Sorhannus, U. (2007). A nuclear-encoded small-subunit ribosomal RNA timescale for diatom evolution. Marine Micropaleontology 65: 1-12.

Title Illustrations
Click on an image to view larger version & data in a new window
Click on an image to view larger version & data in a new window
Asterionellopsis valve
Scientific Name Asterionellopsis glacialis
Comments Transmission electron micrograph of basal section of valve, with pore field
Creator Frank E. Round
Acknowledgements This image is derived from the Professor Frank Round Image Archive at the Royal Botanic Garden Edinburgh
Specimen Condition Dead Specimen
Identified By David Mann
Life Cycle Stage Vegetative phase
Body Part Valve
View Whole mount
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2008 David G. Mann
Dimeregramma: dividing frustule
Scientific Name Dimeregramma
Creator Frank E. Round
Acknowledgements This image is derived from the Professor Frank Round Image Archive at the Royal Botanic Garden Edinburgh
Specimen Condition Dead Specimen
Identified By David Mann
Life Cycle Stage Vegetative phase
Body Part Dividing frustule
View Exterior, SEM
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2008 David G. Mann
Rhaphoneis valve
Scientific Name Rhaphoneis amphiceros
Specimen Condition Dead Specimen
Identified By David Mann
Life Cycle Stage Vegetative phase
Body Part Valve
View Interior, SEM
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2008 David G. Mann
About This Page

This page is being developed as part of the Tree of Life Web Project Protist Diversity Workshop, co-sponsored by the Canadian Institute for Advanced Research (CIFAR) program in Integrated Microbial Biodiversity and the Tula Foundation.

David G. Mann
Royal Botanic Garden Edinburgh, United Kingdom

Correspondence regarding this page should be directed to David G. Mann at

Page: Tree of Life clade I araphid pennate diatoms. Authored by David G. Mann. The TEXT of this page is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

Citing this page:

Mann, David G. 2010. clade I araphid pennate diatoms. Version 07 February 2010 (under construction). http://tolweb.org/clade_I_araphid_pennate_diatoms/125304/2010.02.07 in The Tree of Life Web Project, http://tolweb.org/

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