Navithidium gen. nov., a new monoraphid diatom (Bacillariophyceae) genus based on Achnanthes delicatissima Simonsen

Abstract

We investigated the ultrastructure of Achnanthes delicatissima Simonsen in materials collected from the Swedish Baltic coast. Valve structure differs markedly from that of Achnanthes sensu lato, particularly in the absence of cribrate areolae which separates Achnanthes from all other members of the family Achnanthaceae. Comparing this species with those recently described achnanthoid genera, such as Scalariella Riaux-Gobin & Witkowski and Madinithidium Witkowski, Desrosiers & Riaux-Gobin revealed morphological differences that warrant the erection of a new genus, Navithidium. Owing to the small size of the frustules, it is difficult to identify Navithidium delicatissima in light microscopy due to similarities with some closely related taxa like Achnanthidium pseudochamaepinnularia (which is here transferred to Navithidium). A comparison with related genera is provided and discussed.

Two New Species of Achnanthidium Kützing (Achnanthidiaceae) from the Quaternary Sediments of the Colônia Basin, Southeast Brazil

“…Currently, Achnanthidium covers monoraphid species having the following features: linear to lanceolate-elliptic valve outlines, uniseriate striae that are spaced wider in the center and denser toward the valve apices, a straight central raphe hardly expanded at the center and straight or turned to one side at the apex and a row of elongate areolae on the mantle (Round & Bukhtiyarova 1996). Nevertheless, several of these features cannot be easily observed under light microscopy (LM), often hampering identification and preventing the valve ultrastructure from being clearly examined (Al-Handal et al . 2021).…”