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 : 6-17

Lyreneis undulata sp. nov. ( Figs 3–31 )

Holotype (designated herein): The individual illustrated in Fig. 7 , on slide TNS AL-66008 s in TNS ( Department of Botany , National

Museum of Nature and Science , Tokyo). Isotype (raw material; designated herein): TNS AL- 66008m ( Fig. 11 ) Type locality: Imazu tidal flat, Fukuoka, Japan. 130°15′4.13″E, 33°35′48.39″N ( Fig. 2 and Table 1). Collected from the surface of the mud flat ( Fig. 2 ) by Muto and T. Chiba, February 18, 2023 .

Etymology: From the Latin undulata, “wavy,” after its undulating frustule.

Habitat: Epipsammic on sand in brackish or marine mud (epipelic) flats.

Description: —Valves rhombic to elliptical rhombic in shape. Length 88–155 μm and width 38–46 μm. Axial area narrow, central area rounded. Axial part of the valve surface elevated towards both ends of the valve. Valve surface striate, 10–11 in 10 μm, and striate punctae, 8–11 in 10 μm, radial in the middle as well as at the apices. Girdle consists of a few open bands. Perforations composed of relatively robust areolae, in single row. Concave area along the raphe present. The bottom of the mantle at the terminal ends extends in a slightly rostrate manner toward the deeper mantle direction (pervalvar axis).

Under LM, L. undulata exhibits two H-shaped pale yellow-brown chloroplasts, each touching the inside of the frustules ( Figs 3, 4 ). The nucleus is located in the centre so that it touches the frustules ( Figs 3, 4 ). These features are characteristics of both Lyrella and Petroneis ( Round et al. 1990; Mann & Stickle 1993; Jones et al. 2005, Table 2). Valves appear as a rhombus to elliptical rhombus in outline, with the terminal end bulging upwards ( Figs 6–13 ); however, no clear lateral areas are observed. The central area is large rounded or slightly rhombic. The central nodule is very clearly recognized, and the central fissure is also clearly recognized ( Figs 6–13 ). Because the axial part between the apical ends appears concave along the raphe, it is not possible to focus on the entire valve face under LM; however, punctae are observed to be arranged relatively regularly radially. A characteristic of the decrease in the frustule size resulting from cell division is that the variation in the width is small relative to the length ( Figs 6–13 ). Specimens of L. undulata are often tilted to the left or right of their apical axis ( Fig. 9 ). This tilt is caused by the protruding structure at the bottom of the mantle, recognized by SEM observation.

Under SEM, the most notable feature of L. undulata is the presence of raised and slightly depressed areas along the raphe ( Figs 14–17 , Table 2). The slightly depressed area along the raphe is recognized at a position corresponding to the lateral area of Lyrella such as in Lyrella lyra (Ehrenberg) Karajeva ( Karajeva 1978: 1595) ( Jones et al. 2005) ( Figs 32–36 ). Their structure causes the valve to undulate, forming a concave cylindrical shape in external view ( Fig. 15 ). The height of valve face, except for the apical axis ridge along the raphe, gradually decreases to deep mantle direction towards the terminal end. The punctae become less dense nearer to the raphe as seen, for example, in Petroneis granulata D.G.Mann ( Round et al. 1990: 675) ( Jones et al. 2005). The external central fissure is Tshaped ( Figs 18–20 ), and the internal central fissure is hook-shaped ( Figs 21–23 ). The central nodule is very clearly recognized, and the central fissure is also obvious ( Figs 21–23 ). In external view, punctae density is high near the edges and sparser near the raphe through the concave part of the valve. Between the edges and the raphe, punctae are placed at relatively equal intervals ( Figs 14, 15 , 24–26 ). In internal view, flaps of silica (volate occlusions) are recognized as in Petroneis marina (Ralfs) D.G.Mann ( Round et al. 1990: 675) ( Jones et al. 2005) ( Figs 37–41 ). Therefore, under LM the pattern of punctae appears larger and clearer than it actually is. The bottom of the valve (mantle) at the terminal ends extends in a slightly rostrate manner toward the mantle direction (pervalvar axis) ( Figs 17 , 24, 25, 27 ). This valve edge structure is easily damaged and is often lost. No complete bands were found, but the pores appear to be arranged in a single row in each open band. In Lyrella , each band bears one transverse row of pores; in Petroneis there is one or two rows per band ( Round et al. 1990).

Comparison of L. undulata with Lyrella lyra and Petroneis marina obtained from Imazu tidal flat revealed distinctive features of each species. Furthermore, morphological comparisons were performed with 21 species of the genera Lyrella , Petroneis Moreneis , and Petroplacus for which internal views could be confirmed by SEM images. Lyreneis undulata is distinct from these existing species ( Table 2). The species considered were Lyrella abruptapontica Nevrova, Witkowski, Kulikovskiy & Lange-Bert. in Nevrova et al. (2013: 3), Lyrella aestimata (Hustedt) Nevrova, Witkowski, Kulikovskiy & Lange-Bert. in Nevrova et al. (2013: 24), Lyrella atlantica (A. Schmidt) D.G.Mann in Round et al. (1990: 671), Lyrella barbara (Heiden in Heiden & Kolbe) D.G. Mann in Round et al. (1990: 671), Lyrella cassiteridum D.G. Mann (1998: 507) , Lyrella dilatata (A. Schmidt) Nevrova, Witkowski, Kulikovskiy & Lange-Bert. in Nevrova et al. (2013: 23), Lyrella hennedyi (W.Smith) Stickle & D.G.Mann in Round et al. (1990: 672) ( Mann 1993), Lyrella karayevae Nevrova, Witkowski, Kulikovskiy & Lange-Bertalot in Nevrova et al. (2013: 11), Lyrella majuscula (Hustedt) Witkowski in Moser et al. (1998: 353), Lyrella ruppelii Nevrova, Witkowski, Kulikovskiy & Lange-Bertalot in Nevrova et al. (2013: 8), Petroneis granulata (Appendices 1, 2), Petroneis humerosa (Brébisson ex W.Smith) Stickle & D.G.Mann in Round et al. (1990: 674), Petroneis latissima (W.Gregory) Stickle & D.G.Mann in Round et al. (1990: 674), Petroneis plagiostoma (Grunow) D.G.Mann in Round et al. (1990: 674), Petroneis sp. (Appendices 3–5), Moreneis angulata J.Park, Koh & Witkowski in Park et al. (2012: 191), Moreneis coreana J.Park, Koh & Witkowski in Park et al. (2012: 190), Moreneis granulata J.Park, Koh & Witkowski in Park et al. (2012: 192), Moreneis sp. (Appendices 6, 7), Petroplacus lizae Pomazkina, Rodionova, Sherbakova & D.M.Williams in Pomazkina et al. (2016: 269), and Petroplacus tectum Pomazkina, Rodionova, Sherbakova & D.M.Williams in Pomazkina et al. (2016: 270).

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Comparison with Navicula brasiliensis Grunow ( Schmidt 1874: Tafel 6) (in Stidolph et al. 2012) and Navicula carinifera Grunow (in Stidolph et al. 2012; Al-Handal et al. 2018) revealed that L. undulata is morphologically distinct from these existing species ( Table 3).

The L. undulata specimens isolated from Imazu tidal flat in the present study fell within a sister taxon of the group Lyrella including Lyrella hennedyi , Lyrella sp. , and Lyrella atlantica (A.W.F.Schmidt) D.G.Mann in Round et al. (1990: 671).

(2012), Navicula carinifera in Al-Handal et al. (2018) and Cleve (1894), and Navicula scandinavica in Cleve (1894).

Figures

FIGURES 3–5. Living cells of Lyreneis undulata. (3) Valve view. ch in arrows showing chloroplasts, nu in arrows showing nucleus and py in arrows showing pyrenoid. (4) Girdle view. ch in arrows chloroplasts and nu in arrows showing nucleus. Scale bar = 10 μm. (5) Valve view. Living cell attached to a sand grain. Scale bar = 10 μm.

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).

FIGURES 1–2. Study area using Google Earth images. (1) Location of Imazu tidal flat in Japan. (2) Locations of sampling sites (s1– s16).

FIGURES 32–36. LM and SEM images of Lyrella lyra obtained from Imazu tidal flat. (32) LM image. (33, 35, 36) SEM image of the external view. (34) SEM image of the internal view. Scale bar = 10 μm in (32, 33) and 5μm in (34–36).

FIGURES 37–41. LM and SEM images of Petroneis marina obtained from Imazu tidal flat. Scale bar = 10 μm in (37–39) and 5 μm in (40, 41). (37) LM image. (38, 40, 41) SEM image of the external view. (39) SEM image of the internal view.