The Mathematical Biology of Diatoms

4Ring to the Linear: Valve Ontogeny Indicates Two Potential Evolutionary Pathways of Core Araphid Diatoms

Shigeki Mayama^1,2* and Momoko Kushida^3,4

¹ Advanced Support Center for Science Teachers, Tokyo Gakugei University, Koganei, Tokyo, Japan

² Tokyo Diatomology Lab, 2-3-2 Nukuikitamachi, Koganei, Tokyo, Japan

³ Department of Biology, Tokyo Gakugei University, Koganei, Tokyo, Japan

⁴ Takasago Elementary School, Urawa, Saitama, Japan

Abstract

The morphogenesis of diatom valves proceeds from the center, following one of two specific patterns. In centrics, there is a ring-shaped annulus, and pennates have a linear sternum. Pennate diatoms are evolutionarily derived from centric diatoms; however, the transition in valve morphogenesis pattern type from ring-shaped to linear remains unclear. Among pennates, raphid diatom valve formation has been examined by many researchers. However, investigation of araphid diatoms is limited. Herein, we observed sequential valve development in two araphid diatoms using electron microscopy. Fragilaria mesolepta has a narrow linear sternum in its mature valve. However, a single silicified chain comprising several rings appeared in earlier developmental stages. The rings comprised a series of spherules with an indistinct periphery ~55–75 nm in diameter with a core of ~30–40 nm. This chain was associated with laterally developing short ribs (virgae), which were aligned radially at one pole with bifurcation. The chain was short in the early stage but ...