Simonsenia aveniformis sp. nov. (Bacillariophyceae), molecular phylogeny and systematics of the genus, and a new type of canal raphe system.

Andrzej Witkowski,Przemysław Dąbek,Michael Harrison,Tomasz Boski,Chunlian Li,Izabela Zgłobicka,Rosa Trobajo,Ana Gomes,Frederik Barka,David G Mann,Justyna Grzonka,Evgeniy Gusev,Krzysztof J Kurzydłowski

doi:10.1038/srep17115

Abstract

The genus Simonsenia is reviewed and S. aveniformis described as new for science by light and electron microscopy. The new species originated from estuarine environments in southern Iberia (Atlantic coast) and was isolated into culture. In LM, Simonsenia resembles Nitzschia, with bridges (fibulae) beneath the raphe, which is marginal. It is only electron microscope (EM) examination that reveals the true structure of the raphe system, which consists of a raphe canal raised on a keel (wing), supported by rib like braces (fenestral bars) and tube-like portulae; between the portulae the keel is perforated by open windows (fenestrae). Based on the presence of portulae and a fenestrated keel, Simonsenia has been proposed to be intermediate between Bacillariaceae and Surirellaceae. However, an rbcL phylogeny revealed that Simonsenia belongs firmly in the Bacillariaceae, with which it shares a similar chloroplast arrangement, rather than in the Surirellaceae. Lack of homology between the surirelloid and simonsenioid keels is reflected in subtle differences in the morphology and ontogeny of the portulae and fenestrae. The diversity of Simonsenia has probably been underestimated, particularly in the marine environment.

Highlights

The genus Simonsenia is reviewed and S. aveniformis described as new for science by light and electron microscopy
Simonsenia Lange-Bertalot is a genus of motile, raphe-bearing diatoms in which the raphe system opens into a longitudinal canal on a marginal keel[16]
It was only when electron microscopy was used to study S. delognei that it became evident that the structure of the raphe system differs from that of Nitzschia and that, in some respects, it more closely resembles some Surirellaceae

Summary

Introduction

The genus Simonsenia is reviewed and S. aveniformis described as new for science by light and electron microscopy. The monoraphid diatoms, represented by the Achnanthaceae on the one hand, and the Cocconeidaceae and Achnanthidiaceae on the other, have turned out to be distantly positioned, each being related to a different biraphid family[11,12] (Ashworth et al 201312: Fig. S1); recently a third group of monoraphid diatoms has been identified and these cluster together with the Stauroneidaceae[13] It is clear, that the loss of the raphe from one valve of each cell in monoraphid diatoms, and from both valves in some other diatoms, e.g. Diadesmis and Diprora[11,14,15], has occurred repeatedly. Ruck and Kociolek[22] included S. delognei as one of the terminal species in a formal cladistic analysis of diatoms possessing a canal-raphe Their analysis, which was based on morphological characters, supported one of Lange-Bertalot’s conclusions – that Simonsenia should be placed in the Bacillariaceae (a conclusion followed by23–27) – but did not support the idea of a relationship to the Surirellaceae. This conclusion has not been tested using molecular phylogenetic approaches

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