Synonyms: Lithothamnium decussatum Solms-Laubach (1881) p. 14; Mesophyllum philippii (Foslie) Adey (1970) p. 25.

VEGETATIVE FEATURES

Thallus habit: encrusting hard rocks, rarely free-living. Sometimes formed by adventitious lamellae and sparsely mamillate (arising from basal crust whichis fixed with its whole lower layer). Often free margin, rarely revolute; edge paler than thallus and slightly thickened. Size: very variable diameter, 0.3-8mm thick. Colour of living specimen: pink pale violet. Colour of dried specimen: white yellowish.

Basal crust: multistratose. Medulla: multilayered with ovoid cells, filaments loosely aggregated (A), straight; presence of densely pigmented zones; cells 15 (20)µm long x (6) 9µm in diameter. Cortex: multilayered with rectangular to ovoid cells in more or less interweaved, very developed (A); cells 15-24 (32)µm long x 8-12µm in diameter. Epithallial cells: with flattened and flared walls 6-8µm in diameter (B). Cell connections: cell fusions.

Conceptacles: prominent, wart like (C), sometimes very densely grouped and therefore deformed; 0.8-1mm diameter. Gametangial conceptacles: carpogonial smaller than the others, bearing a thorn; spermatangial: --- Tetra/bisporangial conceptacles: multiporate (about 70 pores), in v.s. circular to elliptical (D), with apical plugs; 800-1000µm outer diameter, 400-420µm in diameter x 150-200µm high. Phenology: ---

Habitat: species characteristic of deep environments, recorded in shady sites where together with Spongites fruticulosa and Lithophyllum stictaeforme contributes to calcareous organogenous build-ups, often reported on Laminariales rhizoids. Bathymetric distribution: from sublittoral to 25-80m deep. Geographic distribution (Babbini & Bressan 1997):

Alboran Sea (A): Morocco; Western Mediterranean Sea (African shores) (B): Algeria; Middle Western Mediterranean Sea (C): Spain, France, Italy; North Western Mediterranean Sea (D): Spain, France, Italy; North Adriatic Sea (E): Italy, Croatia; Middle Adriatic Sea (F): Italy, Croatia; South Adriatic Sea (G): Italy; South Eastern Mediterranean Sea (H): Italy, Libya; Middle Eastern Mediterranean Sea (L): Italy.