Marine necklace‐chain Fragilariaceae (Bacillariophyceae) from Guam, including descriptions of Koernerella and Perideraion, genera nova

Abstract

Light microscopy (LM) and scanning electron microscopy (SEM) studies of necklace-chain forming colonial diatoms from benthic habitats in Guam revealed five species. Bleakeleya notata (Grunow in Van Heurck) Round is widespread and well-known. Asterionella notata var. recticostata Körner has been reported only twice before; we describe the plastids for the first time. On phylogenetic grounds we assign A. notata var. recticostata to a new genus, Koernerella, and emend the description of Bleakeleya. Three new species belonging in a new genus, Perideraion, are described as P. montgomeryi, P. decipiens and P. elongatum. Cultures from single-cell isolates yielded four gene sequences for three of these taxa. The genera are easy to identify in the LM and SEM. Perideraion differs from Bleakeleya and Koernerella in having two large H-shaped plastids, as reported for Asterionellopsis and Asteroplanus, and is further distinguished from all these genera by the following character set: a distinct rim around the basal field of circular pores, an apical rimoportula laterally on the valve mantle, pores in the valves that are unlike those in the basal pore field, and absence of apical slits. Although the basal pole attachment and colony morphology seem synapomorphic, molecular evidence suggests that the Bleakeleya-Koernerella-Perideraion clade is separate from the Asterionellopsis-Asteroplanus clade and these five genera do not form one monophyletic group. It remains to be seen whether they are part of a somewhat larger group at the base of the araphid grade or if the genera we studied are truly separate.

Revisiting Ross and Sims (1971): toward a molecular phylogeny of the Biddulphiaceae and Eupodiscaceae (Bacillariophyceae)

“…The term “ocellus” has been used to describe several different structures, such as the apical pore field in the araphid pennate diatom Bleakeleya Round and is discussed in Lobban et al. ().…”

Hanicella moenia, gen. et sp. nov., a ribbon‐forming diatom (Bacillariophyta) with complex girdle bands, compared to Microtabella interrupta and Rhabdonema cf. adriaticum: implications for Striatellales, Rhabdonematales, and Grammatophoraceae, fam. nov.

“…Observations of fresh and acid cleaned materials were carried out at U. Guam and U. Texas, Austin, as in previous work (Lobban et al. , , Ashworth et al. ).…”

“…) and description of several new species has led to improved understanding of some little‐known genera (Lobban et al. , , Ashworth et al. , Lobban ) and contributed to phylogenetic studies (Theriot et al.…”

Centric and Araphid Diatoms

“…There may be at least five species in the Laurentian Great Lakes. A later study that included additional more closely related groups, showed that the two subgenera, although distinct, were not necessarily one another's sister group, with Odontidium instead most closely related to Tabellaria and Tetracyclus (Williams, 1989;Lobban et al, 2011). Frustules are rectangular in girdle view.…”

“…All of these genera are, according to recent molecular data, most closely related among themselves and a few other marine "araphid" groups (Lobban et al, 2011). The freshwater species of Asterionella, according to both morphological data and molecular data (Williams, 1989;Lobban et al, 2011), are most closely related to other freshwater genera, such as Diatoma, Odontidium, and Tabellaria.…”