Generic limits within the Eupodiscaceae: I. Observations on three unusual species of Cerataulus, with reference to the type species, C. turgidus

Abstract

Scanning electron and light microscope observations are presented of Biddulphia brittoniana Kain & Schultze, B. heteroceros Grunow and B. multicornis Grunow. All these species possess unusual modes of chain formation, including entangling spines and clasping of the external tubes of the rimoportulae. The three species are transferred to Cerataulus Ehrenberg based on their loculate valve structure, rows of areolae with internal foramina and external groups of fine pores interrupted by spinules and locular walls, the presence of ocelli pointing away from the apical axis, and of a sipho marginalis. Observations on C. turgidus (Ehrenberg) Ehrenberg, the type species of this genus, are also provided, and the generic description is emended. Morphological features that separate Cerataulus from Pleurosira (Meneghini) Trevisan, Odontella C. Agardh and Zygoceros Ehrenberg are discussed. The overall good preservation of the materials examined here also provides new insights into the structure of the sipho marginalis.

Keywords:

• fossil and recent diatoms
• morphology
• Cerataulus
• Biddulphia sensu lato
• taxonomy
• sipho marginalis

Acknowledgements

We wish to thank Klaus Kemp for providing cleaned and mounted materials from Poole Harbour and Tampa, and R.W. Holmes for providing the cleaned material from the A.L. Brigger collection. Andrzej Witkowski, Laia Rovira and Rosa Trobajo i Pujadas kindly provided some of the SEM micrographs presented here. Alex Ball is thanked for help during the SEM sessions. Jelena Godrijan, Suncica Bosak and Tsuyoshi Watanabe are thanked for providing literature. Anton Igersheim provided information about the contents of the Grunow Collection, housed at Naturhistorisches Museum, Vienna. Comments and suggestions from Michel Poulin and two anonymous reviewers helped to improve this paper. In particular, we thank one of the reviewers for providing valuable advice and references on the stratigraphy of the Maido Formation, Aomori Prefecture, Japan.