Synonyms: (basynonim) Melobesia cystoseirae Hauck (1883) p. 266; Lithophyllum cystoseirae Heydrich (1897) p. 60; Dermatolithon papillosum Foslie (1909) p. 58; Dermatolithon cystoseirae (Hauck) H.Huvé (1962) p. 234.

VEGETATIVE FEATURES

Thallus habit: encrusting, without excrescences, rounded to orbicular; thalli often confluent and fused. It may form  calcareous sleeve. Adherent or free,  therefore curled, thin margin; lobed, more or less white edge (A). Size: diameter up to 12-15mm, (0.05) 0.2-0.3 (0.6)mm thick. Colour of living specimen: from violet grey to wine red. Colour of dried specimen: mauve grey (violet grey). 

Basal crust: multistratose thallus. Basal filaments: palisade cells (B), with cell walls more or less sinuate: 5-10µm long x (10) 30-50 (80)µm in diameter. Erect filaments: rectangular cells with thin walls, sometimes arranged in layers of different height, very irregular, 2-4 overlapping layers also: (7) 20-60 (80)µm long x (3) 7-10µm in diameter or 14-125µm long x 14-19µm in diameter. Epithallial cells: quite isodiametric, triangular in longitudinal section, large as lower cells, diameter up to 12µm. Cell connections: secondary pit-connections (numerous and clearly visible). Other features: trichocytes occasionally present.

Gametangial conceptacles: carpogonial, 300-400µm in diameter x 175µm high; spermatangial, 70µm in diameter x 70µm high. Tetrasporangial conceptacles: uniporate, convex, slightly raised (C); elliptical chambers 307-324µm in diameter x 80-124µm high. Bisporangial conceptacles: uniporate, elliptical chambers: 288-475µm diameter x 80-172µm high or ex.: 200-280µm x 200µm. Phenology: ---

Habitat: epiphytic, particularly on different algal speciesand seagrasses: Cystoseira, Gymnogongrus, Gelidium, Valonia, Phyllophora, Codium, Posidonia, Sargassum. Bathymetric distribution: lower littoral, from water surface to 65m deep. Geographic distribution: (Babbini & Bressan 1997):

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

Notes: H.Huvé (1962) has reported that the two species have been confused under the name of Dermatolithon papillosum; these two species at present are known under the names of Goniolithon papillosum (Zanard.) Fosl. and Titanoderma cystoseirae (Hauck) Woelkerling et al.