Synonyms: Sporolithon mediterraneum Heydrich (1899b) p. 227; Archaeolithothamnium mediterraneum (Heydrich) Foslie (1901) p.8.

VEGETATIVE FEATURES

Thallus habit : encrusting, flattened or with numerous protuberances; recorded free-living as a rhodolith. Size: diameter up to 20cm, up to 5mm thick. Colour of living specimen: red-pink to brownish. Colour of dried specimen: from red-pink to brownish or grey mauve. 

Medulla: 3-4 filaments of cells, thickness rarely more than 200µm; rectangular cells: 12-47µm long x 4-8µm in diameter. Cortex: squarish to rectangular cells: 5-13µm long x 4-8µm in diameter. Epithallial cells: single, more or less elliptical, with flared cell walls (A): 2-5µm long x 6-11µm in diameter. Cell connections: both cell fusions and secondary pit-connections present (B) (secondary pit-connections are less numerous in the cortex than cell fusions).

Gametangial conceptacles: unknown. Tetrasporangial sori: grouped. Each uniporate tetrasporangial chamber (C) is lemon-shaped (D): outer diameter 86-100µm x 39-51µm high. Paraphyses between adjacent sporangi are 4-6 cells long. Pore diameter 12µm, rosette of 8-11 cells (26µm diameter), pore canal length 10-12µm. Other features: presence of a layer of long cells under tetrasporangial chambers (C) [18-23 (25)µm x (5) 6-9 (10)µm]. Old and empty tetrasporangial conceptacles become buried in distinct layers of thallus.

Habitat: on rocky bottoms with presence of currents, recorded also in littoral pools. Bathymetric distribution: littoral and sublittoral. Geographic distribution (Babbini & Bressan 1997).

Middle Western Mediterranean Sea (C): Spain, Italy; North Western Mediterranean Sea (D): France; North Adriatic Sea (E): Italy; Middle Adriatic Sea (F): Italy; Middle Eastern Mediterranean Sea (H): Malta.