Hydrolithon sp.

Villas-Bôas, Alexandre B., Riosmena-Rodriguez, Rafael, Tâmega, Frederico T. S., Amado-Filho, Gilberto M., Maneveldt, Gavin W. & Figueiredo, Marcia A. O., 2015, Rhodolith-forming species of the subfamilies Neogoniolithoideae and Hydrolithoideae (Rhodophyta, Corallinales) from Espírito Santo State, Brazil, Phytotaxa 222 (3), pp. 169-184 : 175-177

Hydrolithon sp.

Plants non-geniculate, pink to dark purple, encrusting to lumpy ( Fig. 14). The internal thallus construction is pseudoparenchymatous and monomerous ( Fig. 16 ). The core region is non-coaxial (plumose) and comprises square to elongate cells that measure 9–20 μm long by 3–5 μm in diameter. Peripheral filaments are comprised of more or less square to rectangular cells that measure 5–6 μm long by 3–5 μm in diameter. Peripheral filaments are terminated by a single layer of rounded epithelial cells that are about 3 μm long by 3 μm in diameter. Sub-epithelial initials are rectangular and measure 8–11 μm long by 3–6 μm in diameter. Cells of adjacent filaments are joined by cell fusion ( Fig. 15 ), secondary pit connections and trichocytes have not been observed. Gametangial plants have not been observed. Mature tetra/bisporangial conceptacles are uniporate and have flush to raised roofs. Conceptacle roofs are 8–9 (including epithelial) cells thick and are formed from filaments surrounding and interspersed among the sporangial initials. The bases of the pore channels are lined by enlarged cells that measure 23–30 μm long by 11–15 in diameter ( Fig. 18 ), these cells do not protrude into the pore canal, but are orientated vertically. Conceptacle chambers are elliptical and measure 127–142 μm in diameter by 140–153 μm in height ( Fig. 17 ). The conceptacle chamber floor is situated 17–18 cell layers below the surrounding thallus surface. Sterile paraphyses (columellae) were observed to persist at the center of the conceptacle chambers ( Fig. 17 ). Mature tetrasporangia measure 47–49 μm long by 27–28 μm in diameter and contain tetraspores at the periphery of the conceptacle chambers ( Fig. 17 ).

Ecological observations:—Plants forming multispecific rhodoliths, 3–30 cm in diameter. At 17–30 m depth, Hydrolithon sp. is one of the most abundant rhodolith-forming non-geniculate coralline algal species.

Geographical distribution:— Espírito Santo State, Brazil.

Distribution in the study sites:— Hydrolithon sp. was found at three sites.

Examined material:— BRAZIL. Espírito Santo State (20° 50’ 00” S, 40° 27’ 00” W, 18 January 2006, F. T. de S. Tâmega, RB 472398 ); (20° 51’ 00” S, 40° 28’ 00” W, 18 January 2006, F. T. de S. Tâmega, RB 480486 ) ; 20° 53’ 00” S, 40° 30’ 00” W, 18 January 2006, F. T. de S. Tâmega, RB 480487 ).

Diagnostic features:— Hydrolithon sp. differs from other Hydrolithon species in having the following combination of features: 1) mature tetrasporangial conceptacles measure 140–153 μm in height, and 2) mature tetrasporangial conceptacles bearing a central columella, possessing roofs usually 8–9 cells thick and the conceptacle chamber floor is situated 17–18 cell layers below the thallus surface.

Key to the rhodolith-forming species of Hydrolithoideae and Neogoniolithoideae from Espírito Santo State, Brazil

1. Internal thallus construction monomerous with a core region comprised of coaxial filaments .......................................................... ..................................................................................................................................................... Neogoniolithon cf. brassica-florida

- Internal thallus construction monomerous with a core region comprised of plumose (non-coaxial) filaments...............................2

3. Mature tetrasporangial conceptacle chambers lacking a central columella; tetrasporangia arranged across the floor of the conceptacle chamber .............................................................................................................................................................. Hydrolithon rupestre

- Mature tetrasporangial conceptacle chambers bearing a central columella; tetrasporangia arranged along the periphery of the conceptacle chamber ................................................................................................................................................... Hydrolithon sp.

Figures

FIGURES 15–18. Hydrolithon sp. 15. Longitudinal sections showing cell fusions (black arrow) and rounded epithelial cells (grey arrow). Scale = 9 μm. 16. Monomerous thallus. Scale = 20 μm. 17. A tetrasporangial conceptacle with a tetrasporangial pore canal showing great thickness in tetrasporangial roof, with 8–9 cell layers. Scale = 30 μm. 18. Detail of a tetrasporangial conceptacle pore canal. Enlarged cell vertically orientated along the pore canal. Scale = 13 μm.