Pseudostriatella (Bacillariophyta): a description of a new araphid diatom genus based on observations of frustule and auxospore structure and 18S rDNA phylogeny

Abstract

S. Sato, D.G. Mann, S. Matsumoto and L.K. Medlin. 2008. Pseudostriatella (Bacillariophyta): a description of a new araphid diatom genus based on observations of frustule and auxospore structure and 18S rDNA phylogeny. Phycologia 47: 371–391. DOI: 10.2216/08-02.1

Pseudostriatella oceanica gen et. sp. nov. is a marine benthic diatom that resembles Striatella unipunctata in gross morphology, attachment to the substratum by a mucilaginous stalk and possession of septate girdle bands. In light microscopy, P. oceanica can be distinguished from S. unipunctata by plastid shape, absence of truncation of the corners of the frustule, indiscernible striation and absence of polar rimoportulae. With scanning electron microscopy, P. oceanica can be distinguished by a prominent but unthickened longitudinal hyaline area, pegged areolae, multiple marginal rimoportulae and perforated septum. The hyaline area differs from the sterna of most pennate diatoms in being porous toward its expanded ends; in this respect, it resembles the elongate annuli of some centric diatoms, such as Attheya and Odontella. 18S rDNA phylogeny places P. oceanica among the pennate diatoms and supports a close relationship between P. oceanica and S. unipunctata, but the genetic distance between them, coupled with the morphological differences, justifies separation at genus level. However, the affinity of the P. oceanica – S. unipunctata clade remains unresolved both in molecular and in morphological study. Both genera are only distantly related to Hyalosira and Grammatophora, despite similarities in frustule structure and growth habit, arguing against their inclusion in the same family. The auxospore is covered with series of transverse and longitudinal bands, but the structure and arrangement of these bands appear to be more similar to the properizonia of some centric diatoms than to the classic type of perizonium seen in other pennate diatoms; a few scales are also present. The differences between properizonia and perizonia are discussed.

Key Words::

• 18S rDNA
• Araphid diatom
• Auxospore
• Evolution
• Fine structure
• Morphology
• Perizonium
• Phylogeny
• Pseudostriatella oceanica
• Striatella
• Taxonomy

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ACKNOWLEDGMENTS

The authors are grateful to Beth K. Petkus for collection of living specimen and brought us it from the United States to Germany with her, Richard M. Crawford for correction of the manuscript and discussion, Stephan Frickenhaus for establishing parallel processing for Bayesian analyses, Paul A. Fryxell for helping to translate the Latin diagnosis, Friedel Hinz for technical help for LM and SEM, and Masahiko Idei for allowing us to access his poster for the 17th International Diatom Symposium. We also thank two anonymous reviewers for their valuable comments and suggestions. This study was supported by DAAD for doctoral research fellowship to Shinya Sato.