Synonyms: Melobesia farinosa f. borealis Foslie (1905) p. 96; Melobesia farinosa f. callithamnioides Foslie (1905) p. 96; Fosliella farinosa sensu Chamberlain (1983) p. 343 pro parte; Fosliella farinosa f. callithamnioides sensu Chamberlain (1983) (non Hapalidium callithamnioides P. & H. Crouan (1859) nec Melobesia callithamniodes (P. & H. Crouan) Solms-Laubach (1881); Hydrolithon farinosum var. farinosum f. callithamnioides (Foslie) Serio (1994) p. 969.

VEGETATIVE FEATURES

Thallus habit: encrusting or partly non-adherent, flat, more or less orbicular or lobed (A). Entire (B), thin margin often with annular stripes. Size: diameter up to 5mm, up to 0.02mm thick. Colour of living specimen: mauve-pink. Colour of dried specimen: white ivory.

Bistratose thallus. Basal filaments: unilayered, cells: 20µm long x 5-17µm in diameter. Epithallial cells: rounded. Cell connections: cell fusions. Other features: spore germination disc with 4 central cells, 4 lateral cells and often 4 atrophic lateral cells. Terminal, single trichocytes (A-B) present.

Gametangial conceptacles: spermatangial 33-9µm in diameter x 26-44µm high; pronounced “spout”; carpogonial hemispherical, 62-110µm in diameter x 52-83µm high. Tetra/bisporangial conceptacles: uniporate, hemispherical 65-94µm in diameter x 52-78µm high. Phenology: ---

Habitat: species epiphytic on different algal specimens, common also on stones, rocks and shells. Bathymetric distribution: sublittoral. Geographic distribution (Babbini & Bressan 1997):

Western Mediterranean Sea (African shores) (B): Tunisia; Middle Western Mediterranean Sea (C): Spain, France, Italy; North Western Mediterranean Sea (D): Spain; Middle Adriatic Sea (F): Italy; South Adriatic Sea (G): Italy, Croatia; South Eastern Mediterranean Sea (H): Italy; North Eastern Mediterranean Sea (M): Greece.