Lyreneis undulata, Muto & Chiba & Tuji & Horie & Fujibayashi, 2025

Muto, Mizuka, Chiba, Takashi, Tuji, Akihiro, Horie, Yoshifumi & Fujibayashi, Megumu, 2025, A new littoral diatom genus, Lyreneis gen. nov. (Bacillariophyceae, Lyrellales, Lyrellaceae), from southwestern Japan, Phytotaxa 711 (1), pp. 1-27 : 22

Phylogeny of Lyreneis undulata

A phylogenetic tree of L. undulata and related taxa based on rbc L is shown in Fig. 51 . Lyreneis undulata is a sister taxon of the monophyletic group consisting of Lyrella atlantica (Schmidt) D.G.Mann , Lyrella hennedyi (W.Smith) Stickle & D.G.Mann (AY571755.1 Lyrella hennedyi voucher E3462), and Lyrella sp. ; this group of four taxa is a sister taxon to a group consisting of Petroneis humerosa (Brébisson ex W.Smith) Stickle & D.G.Mann and Lyrella hennedyi (MH064099.1 Lyrella hennedyi strain KS A2015-5 Lyr-L53). Under the microscope, L. undulata appears to be morphologically independent from both Lyrella and Petroneis or appears to be close to both genera because it shares some morphological characteristics of both, such as characteristics of the apical axis symmetry and cribra ( Figs 6–31 and Table 2).

Several of our results are at odds with the currently accepted phylogeny of Lyrella and Petroneis . The two strains of Lyrella hennedyi (AY571755.1 Lyrella hennedyi voucher E 3462 in Jones et al. 2005 and MH064099.1 Lyrella hennedyi strain KS A2015-5 Lyr-L 53 in Ashworth et al. 2022) occupy different positions in the molecular phylogenetic tree, and morphological examination of each strain revealed that they are different species. The two species differ greatly in frustule appearance, areola density, and stria density (Appendices 9–12). Moreover, in our results, Lyrella hennedyi (MH064099.1 Lyrella hennedyi strain KS A2015-5 Lyr-L53) belongs to the same clade as Petroneis humerosa ( Fig. 51 ). A species found in coral reefs off the Basra coast in Southern Iraq and classified as Petroneis sp. (Appendix 13) by Al-Handal et al. (2018) is also very important in considering the classification of Lyrella and Petroneis . This species belongs to the genus Petroneis but has a distinct lateral-area-like non-stria area. This species also makes us question the meaning of the morphological differences between Lyrella and Petroneis . Our results suggest that the morphological differences that have been identified, at least in Lyrella and Petroneis are inconsistent with the results of genetic analyses.

Figures

FIGURE 51. The phylogenetic tree of Lyreneis undulata and related strains determined using the Maximum Likelihood (ML) method with rbcL (GTR+G+I) gene. Accession numbers, taxonomic names and strain names follow localities for Japanese strains, and ML, NJ and BI bootstrap support values are indicated on branches (only values above 70 are shown).

FIGURES 6–13. LM images of Lyreneis undulata. Valve views. Scale bar = 10 μm.

FIGURES 14–17. SEM images of Lyreneis undulata. valve views. Lateral areas (lyre-shape structures) are not visible in either external or internal valve view. (13), (14) External valve views. Scale bar = 10 μm. (15), (16) Internal valve views. White arrows showing the concave area. Scale bar = 10 μm.

FIGURES 18–23. SEM images of the central area of Lyreneis undulata. Scale bar = 1 μm. (18–20) External central fissure, showing Tshaped central raphe endings and the central area. (21–23) Internal central fissure and central nodule.The internal views of the central area show hooked raphe endings. The deposition of silica is incomplete and cribra have not yet developed. The central endings of the interior raphe opening are straight, unlike the hooked structure present in fully silicified valves.

FIGURES 24–31. SEM images of Lyreneis undulata. (24–26) External valve views. (27) and (28) Terminal fissure and puncta. The terminal fissure does not reach the tip of the terminal area in the external view. (26) Depression corresponding to the lateral area, puncta and raphe. (30) and (31) Internal valve and girdle views. (27) Terminal fissure and volate occlusions, showing the internal structure of the pole, where the raphe terminates in a helictoglossa. (28) Terminal fissure and helictoglossa. (29) Volate occlusions. (30) and (31) Band (internal views). Scale bar = 1 μm in (24–30) and 10 μm in (31).