Hydrolithon sp. 1

Hrabovský, Juraj, 2019, Reproductive phases of Miocene algae from central Paratethys and their bearing on systematics, Acta Palaeontologica Polonica 64 (2), pp. 417-439 : 429-431

publication ID	https://doi.org/ 10.4202/app.00579.2018
persistent identifier	https://treatment.plazi.org/id/03B7C03D-FF87-FFDF-FF57-FC78FEE2FAE0
treatment provided by	Felipe
scientific name	Hydrolithon sp. 1
status

Treatment

Hydrolithon sp. 1

Material.—Bi/tetrasporophyte ( Fig. 5A), NHM B1834/1 (thin section 21510153); gametophytes and carposporangial conceptacle bearing gametophyte ( Fig. 5B, C), NHM B1833/2 and NHM B 1833/3 (thin sections 21510253), all from early Serravallian, Maksymivka, Ukraine (Carpathian Foredeep).

Description.— Hydrolithon sp. 1 grows on algal reefs encrusting other coralline algae, polychaetes, and sessile foraminifers, collectively developing large stout columnar structures at the top of the reef. The surrounding deposits infilling the cavities contain late Serravallian (Sarmatian) fauna. Vegetative anatomy is based on bi/tetrasporic plant. Growth form is encrusting without applanate branches. Surface is undulate with weakly projecting conceptacles. Individual thalli are 168–624 μm thick ( Fig. 5A 1 View Fig ). Thallus is pseudoparenchymatous with dorsiventral internal organisation and dimerous construction ( Fig. 5A 2). Primigenous filaments consist of non-palisade cells, rectangular to flattened cells, or polygonal cells. Cells are 14–25 μm H (mean ± SD: 14 ± 4.4 μm) and 9–23 μm L (mean ± SD: 16 ± 3.9 μm) (n = 19). Cells of postigenous filaments are 7–31 μm L (mean ± SD: 16 ± 6.3 μm) and 6–21 μm D (mean ± SD: 11 ± 3.3 μm) (n = 81). Large polygonal cells are scattered in the tissue, always producing two smaller cells. Horizontal and vertical cells alignment is missing. Cells are laterally joined with fusions ( Fig. 5A 3). Meristematic cells are as long as cells immediately subtending them ( Fig. 5A 4). Epithallial cells are dome shaped, or flattened ( Fig. 5A 4). Cells are 4–6 μm L (mean ± SD: 4 ± 0.8 μm) and 5–16 μm D (mean ± SD: 8 ± 2.3 μm) (n = 12). Trichocytes are solitare and buried in the thallus ( Fig. 5B, SOM: fig. S1).

Spermatangial conceptacle is small and triangular, buried in the thallus ( Fig. 5B). Only one conceptacle was observed. Chamber is 125 μm D and 25 μm H with cone shaped pore canal 54 μm L and 37 μm W at its base.

Carpogonial and carposporangial conceptacles occur on the same thallus. Carposporangial is non-columellated, while carpogonial possess weak columella ( Fig. 5C 1 View Fig ). Carpogonial conceptacles are 109–133 μm D and 76–97 μm H (n = 3). Pore canal is cylindrical 69–96 μm L and 37– 42 μm W ( Fig. 5C 1 View Fig ). Carposporangial conceptacle is 231 μm D and 104 μm H. The roof is 62 μm thick. Roof filaments oriented parallel with the chamber, still remain on some spots ( Fig. 5C 2).

Bi/tetrasporangial conceptacles are developed from cells peripheral to and interspersed among sporangial initials ( Fig. 5A 5). Roof consists of cells smaller than other thallus cells. Pore canals are cylindrical or slightly tapering to its top 64–82 μm L and 41–43 D. Pore canal is lined by 7 celled filaments, perpendicularly oriented to the chamber ( Fig. 5A 5). Chambers could have weak central columella. Chambers are 222–236 μm D (mean ± SD: 229 9.7 μm) and 97–116 μm H (mean ± SD: 107 ± 13.4 μm) (n = 3). External diameter is 239–381 μm and they protrude 50–94 μm above thallus surface.

Remarks.—Species was not reported from the central Paratethys, prior to the present work. Its assessment within the genus Hydrolithon is based on dimerous thallus presence, non-palisade cells in primigenous filaments, lateral fusion of cells, type of the bi/tetrasporic conceptacle development and pore lining cells perpendicularly oriented to the chamber, and presence of trichocytes not arranged in large tightly packed horizontal fields (all corresponding with the diagnosis) ( Kato et al. 2011; Rösler et al. 2016). Basic characteristics documented on selected specimens are listed in Table 6. This species is known only from the early Serravallian of Maksymivka, Ukraine (Carpathian Foredeep).