Mesophyllum engelharti (Foslie) W.H. Adey, 1970: 23

Tâmega, Frederico T. S., Spotorno-Oliveira, Paula, Coutinho, Ricardo & Bassi, Davide, 2016, Taxonomic assessment of fossil Holocene coralline red algae (Rhodophyta, Corallinales, Hapalidiales) from southwestern Atlantic, Phytotaxa 245 (4), pp. 237-250 : 243-244

Mesophyllum engelharti (Foslie) W.H. Adey, 1970: 23 (Figs. 14–17)

Basionym: — Lithothamnion engelharti Foslie, 1900: 18 .

Holotype: — TRH. Dr August Engelhart, Cape Jaffa , South Australia

Type locality: —Cape Jaffa, South Australia, Australia, 1900 ( Woelkerling et al. 2005: 349).

Synonyms: —Complete reference in Chamberlain & Keats (1995).

Age: —Prainhas do Pontal —3,370 –3,185 Cal yrs B. P. (2σ), 1,880 –1,695 Cal yrs B. P. (2σ).

Material examined: — BRAZIL. Rio de Janeiro State, Arraial do Cabo, Prainhas do Pontal (22°59’18.8” S, 42°00’47.1” W, 2.14– 1.97 m above sea level, 14 August 2014, F. T. de S. Tâmega & P. S-Oliveira, IEAPM 00334, IEAPM 00336).

Description: —Thalli non-geniculate, encrusting; internal construction monomerous and dorsiventral with a coaxial medulla composed of concentric arching tiers of rectangular cells (Fig. 14), 8–12 μm in length and 3–6 μm in diameter; peripheral region with filaments composed of rectangular cells, 3–5 μm in length and 3–4 μm in diameter. Cells of adjacent filaments joined by cell fusions; secondary pit connections not observed. Sub-epithallial initials longer than cells immediately subtending them (Fig. 15).

Mature empty sporangial multiporate conceptacles and flush with, to raised above the surrounding thallus surface; conceptacle chambers 262–299 μm in diameter and 122–164 μm in height (Fig. 16). Mature empty male uniporate conceptacles and flush with, to raised above the surrounding thallus surface; conceptacle chambers 127–210 μm in diameter and 92–175 μm in height (Fig. 17).

Remarks: —The presence of cell fusions and multiporate conceptacles in the studied specimens allow them to be placed in the Hapalidiaceae , subfamily Melobesioideae . These features combined with the coaxial growth of the core filaments and with sub-epithallial initials as long or longer than cells immediately subtending them result in placement in Mesophyllum as traditionally circumscribed in fossil material (e.g., Iryu et al. 2009, 2012, Aguirre et al. 2011, 2012, Braga et al. 2015, Hrabovský et al. 2015).

Specimens ascribed to M. engelharti in this study show similarities in their conceptacle characteristics with those previously reported for the species from Australia ( Woelkerling & Harvey 1993), South Africa ( Chamberlain & Keats 1995) and Brazil ( Amado-Filho et al. 2010, Figueiredo et al. 2012, Bahia 2014), with only minor differences in the conceptacle roof height and diameter ( Table 5).

Geographical distribution: —See Guiry & Guiry (2015) for a detailed distribution list.

12) Longitudinal sections of uniporate conceptacles showing the pore canal (pc, arrow); scale bar = 200 μm.

13) Longitudinal sections of uniporate conceptacles showing the pore canal lined by cells protruding laterally into the canal and oriented parallel to the roof surface (arrows point to the direction of the cell filaments); scale bar = 50 μm.

FIGURE 14–17. Mesophyllum engelharti , sample IEAPM 00336, Arraial do Cabo.

14) Longitudinal section of encrusting thallus showing internal construction monomerous and dorsiventral (d—dorsal filaments, v— ventral filaments) with a coaxial medulla and concentric arching tiers; scale bar = 200 μm.

15) Superimposed encrusting thalli of L. pustulatum (Lp) and M. engelharti (Me) illustrating the epithallial cells (e, arrow heads) and subepithallial initials (se, arrow) that are longer than the cells subtending them; scale bar = 50 μm.

16) Longitudinal section of a mature empty tetrasporangial multiporate conceptacles with pore canals (pc, arrows); scale bar = 200 μm. 17) Longitudinal section of a mature male uniporate conceptacle with pore canal (pc, arrow); scale bar = 50 μm.