Fine structure of Delphineis minutissima and D. surirella (Rhaphoneidaceae)

Abstract

Delphineis Andrews is a marine araphid pennate diatom genus belonging to the family Rhaphoneidaceae Forti, which has three distinct subgeneric groups around D. lineata Andrews, D. ovata Andrews and D. surirella (Ehrenberg) Andrews, respectively. Living cells and frustules of three taxa in the D. surirella group were studied using light and scanning electron microscopy. Delphineis minutissima (Hustedt) Simonsen is characterized by small, circular to elliptical valves in which the sternum is as narrow as the virgae. The valve outline of D. surirella is broadly elliptical to lanceolate and the straight sternum is laterally expanded at the apices. Delphineis australis comb. nov. has broadly elliptical valves and a sternum that is slightly narrower at the middle of the valve. Delphineis minutissima and D. surirella share the following fine structure features; no granules, plated rota with two spokes, two rimoportulae per valve and two small pores at each apex. The epicingulum of D. minutissima and D. surirella is composed of several open bands; the first and second bands open at opposite ends, the more distal bands are short.

Keywords:

• Delphineis
• Delphineis australis
• epicingulum
• morphology
• Rhaphoneidaceae
• taxonomy

Acknowledgements

We would like to thank Fusako Mitsuhashi and Takanori Matsuoka for help using the SEM, and Masahiko Idei for help using the epifluorescence microscopy.