Roseolithon sabulosum, Kato & Adachi & Iryu & Baba, 2024

Kato, Aki, Adachi, Kenta, Iryu, Yasufumi & Baba, Masasuke, 2024, Coralline red algal species diversity at a shallow rhodolith bed in warm-temperate Japan, including two new species of Roseolithon (Hapalidiales, Corallinophycidae), Phycologia 63 (6), pp. 520-533 : 526-528

Roseolithon sabulosum Min-Khant-Kyaw, A.Kato & M.Baba sp. nov.

Figures 13–30

DESCRIPTION: Thalli were non-geniculate, warty to fruticose and forming entirely free-living rhodoliths with spheroidal to sub-spheroidal shapes, c. 2 cm wide. In fruticose specimens, branches (protuberances) were up to 7 mm long, apically enlarged (1.5–7.8 mm wide), and dichotomously branched or anastomosing. Colours of living thalli were purplish red to rose pink ( Fig. 13 ). Thallus construction was monomerous with a multistratose non-coaxial (plumose) hypothallus composed of filaments running parallel to the substratum ( Fig. 14 ). Cells of perithallial filaments arose from hypothallial filaments and were composed of square to mostly elongate cells ( Fig. 14 ). Cells of contiguous hypothallial and perithallial filaments were frequently joined by cell fusions ( Fig. 15 ); secondary pit connections were not observed. Subepithallial initials (intercalary meristematic cells) were composed of square to elongate cells, shorter than, approximately equal to or longer than their immediate inward derivatives. A single layer of epithallial cells was flattened with flared outer cell walls (trapezoidal; Fig. 15 ). Trichocytes were not observed. Tetra/bisporangial conceptacles were multiporate, raised above the thallus surface without differentiation into a peripheral rim and pore plate ( Figs 16–18 ). Tetra/bisporangial conceptacles at early developmental stages were flush with or raised above the surrounding thallus surface ( Fig. 18 ) and became overgrown by marginal growth of surrounding vegetative cells when older ( Figs 19–22 ). Each pore opening was surrounded by 4–7 rosette cells in depressions giving a pitted appearance in surface view ( Figs 17, 23 ). Conceptacle roofs were composed of 3–6 cell layers including epithallial cells. Pore canals were blocked by apical plugs before releasing spores and lined by 2–4 celled filaments ( Fig. 24 ). Pore canal filaments include rosette cells with disintegrated roofs and the underlying elongate and/or wedge-shaped cells. Pore canal cells were generally longer than other roof cells ( Fig. 24 ). Tetrasporangia were zonately divided and developed across the entire chamber floor ( Fig. 25 ). Conceptacles appeared to be buried with infilled vegetative cells ( Figs 26, 27 ), but also appeared to be shed. Carpogonial (female) conceptacles were uniporate ( Fig. 28 ) with elliptical chambers ( Fig. 29 ). Carpogonial branches developed across the entire chamber floor of mature conceptacles and were composed of a single supporting cell, a hypogynous cell, and a carpogonium and elongated trichogyne ( Fig. 30 ). Spermatangial (male) and carposporangial thalli were not observed. Data on vegetative and reproductive features are summarized in Table 1 .

HOLOTYPE: SAP 115691 (tetrasporophyte), collected on 21 April 2023 by Min-Khant-Kyaw & A. Kato, deposited in the Herbarium of the Graduate School of Science ( SAP), Hokkaido University, Sapporo, Japan ( Fig. 13 ).

HOLOTYPE GENBANK ACCESSION NUMBERS: psb A, LC822418 ; rbc L-3P, LC822439 ; COI-5P, LC822449 .

TYPE LOCALITY: 32°37.46'N, 130°15.06'E; intertidal; Shirasu , Minami-Arima , Minami-Shimabara City, Nagasaki Prefecture, Japan.

ETYMOLOGY: ‘ sabulosum ’ in reference to the sandy habitat of the type locality.

ADDITIONAL SPECIMEN EXAMINED: In addition to the holotype sequences, nine psb A sequences, five rbc L-3P sequences and three COI- 5P sequences were generated from Japanese specimens ( Table S1 ).

DISTRIBUTION: Based on DNA sequences, R. sabulosum is currently known only from the type locality (Shirasu) and Shikine Island in Japan.

HABITAT: Occurring as free-living rhodoliths in the intertidal zone.

Figures

Figs. 13–15. Habit and vegetative characters of Roseolithon sabulosum sp. nov. Fig. 13. Warty to fruticose holotype specimen (SAP 115691, tetrasporophyte). Scale bar = 1 cm. Fig. 14. Vertical section through the inner thallus showing the monomerous construction, with multistratose non-coaxial hypothallial filaments (h) giving rise to perithallial filaments (p) (SAP 115694). Scale bar = 50 μm. Fig. 15. Vertical fracture through the outer thallus showing a single-layered epithallus (arrows), subepithallial initials (i) and cell fusions (f) between adjacent perithallial filaments (SAP 115697). Scale bar = 10 μm. Inset: Detail of epithallus showing flattened epithallial cells with flared outer walls (trapezoidal) (arrowheads) (SAP 115699). Scale bar = 10 μm.

Figs. 16–27. Tetra/bisporangial conceptacle characters of Roseolithon sabulosum sp. nov. Fig. 16. Surface view showing raised multiporate tetra/bisporangial conceptacles (arrows) (SAP 115691). Scale bar = 500 μm. Fig. 17. Surface view of a raised multiporate tetra/bisporangial conceptacle without differentiation into a peripheral rim and pore plate with depressed rosette cells giving the conceptacle pore plate a pitted appearance (arrows) (SAP 115698). Scale bar = 200 μm. Fig. 18. Vertical fracture through a protuberance showing multiporate tetra/bisporangial conceptacles more or less flush with (arrow) or raised above (double arrowhead) the surrounding thallus surface (SAP 115697). Scale bar = 100 μm. Fig. 19. Surface view showing multiporate tetra/bisporangial conceptacles surrounded by raised vegetative rims (arrows) (SAP 115693). Scale bar = 500 μm. Fig. 20. Surface view of multiporate tetra/bisporangial conceptacles undergoing an enveloping process by the overgrowth of peripheral vegetative rims (arrows) giving conceptacles a volcano-like appearance (SAP 115693). Scale bar = 100 μm. Fig. 21. Vertical fracture through an old multiporate tetra/bisporangial conceptacle about to be fully enveloped due to continuous overgrowth by peripheral vegetative filaments (arrows) (SAP 115698). Scale bar = 100 μm. Fig. 22. Vertical fracture through a recently buried tetra/bisporangial conceptacle as a result of the complete overgrowth by peripheral vegetative filaments (arrow) (SAP 115700). Scale bar = 100 μm. Fig. 23. Surface view of a tetrasporangial conceptacle pore plate with rosette cells in depressions (arrowheads) giving the conceptacle pore plate a pitted appearance (SAP 115698). Scale bar = 50 μm. Inset: Detail of a pore opening (asterisk) bordered by seven rosette cells (1–7) (SAP 115694). Scale bar = 10 μm. Fig. 24. Vertical section through a multiporate tetra/bisporangial conceptacle roof with apical plugs (asterisks) occluding the pore canals, lined by disintegrated rosette cells (arrows) and underlying wedge-shaped pore canal cells (w) (SAP 115691). Scale bar = 50 μm. Fig. 25. Vertical fracture through a mature multiporate tetrasporangial conceptacle bearing a zonately divided tetrasporangium (t) (SAP 115697). Scale bar = 50 μm. Fig. 26. Vertical fracture through a protuberance showing buried conceptacles (arrowheads) (SAP 115696). Scale bar = 500 μm. Fig. 27. Vertical section through the thallus showing a buried tetrasporangial conceptacle with tetrasporangia (t) and infilled vegetative cells (arrows) (SAP 115693). Scale bar = 100 μm.

Figs. 28–30. Carpogonial conceptacle characters of Roseolithon sabulosum sp. nov. Fig. 28. Surface view showing mounded uniporate carpogonial conceptacles (arrows) (SAP 115699). Scale bar = 1 mm. Fig. 29. Vertical section through a young carpogonial conceptacle showing an elliptical chamber (SAP 115699). Scale bar = 100 μm. Fig. 30. Magnified view of the floor of a young carpogonial conceptacle showing carpogonial branches composed of a supporting cell (su), a hypogynous cell (hy) and a carpogonium (ca) extended into an elongated trichogyne (tr) (SAP 115699). Scale bar = 50 μm.