Sinonimi: (basionimo) Millepora calcarea Pallas (1766) p. 265; Millepora polymorpha Linnaeus (1767) p. 1285 (nom. superfl.); Melobesia calcarea (Pallas) Harvey (1849a) p. 110; Lithothamnion calcareum (Pallas) Areschoug (1852) p. 523; Lithothamnion polymorphum (Linnaeus) Areschoug (1852) p. 524 (nom. superfl.); Lithothamnion corallioides f. subsimplex Batters (1892) p. 23; Phymatolithon polymorphum (Linnaeus) Foslie (1898a) p. 4; Lithothamnion calcareum (Batters) Foslie (1905a) p. 68.

VEGETATIVE FEATURES

Thallus habit: encrusting to more or less irregularly branched, not attached, sometimes overlaying the substratum (shells or biogenic remains). Arborescent, free-living adult thalli. Striped margin, sculptured surface; lobed, adherent edge. Size: total diameter up to 6cm (branches diameter up to 6mm). Colour of living specimen: from grey-pink to violet. Colour of dried specimen: from white to mauve grey (dark grey on dead thalli).

Basal crust: multistratose. Medulla: dense tissue formed by 5-6 layers of cells (30-40µm thick), rectangular cells: 10-15µm long x 5-10µm in diameter. Cortex: loosely aggregated filaments (A), multilayered; ovoid cells: 5-10µm x 3-5µm. Subepithallial initial cells are densely pigmented. Epithallial cells: domed, in 2-3 layers, sometimes absent. Cell connections: cell fusions (numerous, only in the cortex) (B).

Gametangial conceptacles: spermatangial not prominent arranged in layers in the outer area of cortex, urn-shaped; 100-140µm in diameter x 60-120µm high. Carpogonial not prominent, ovoid, flattened; 120-150µm in diameter x 60-110µm high. Tetra/bisporangial conceptacles: multiporate (30-60 pores), immersed or slightly raised (C), with orbital ring, ovoid shaped; outer diameter 200-500µm, 120-150µm diameter x 50-60µm high. Phenology: sexual reproduction during September  October, asexual reproduction in different months (September-December).

Habitat: on mobile substrata with currents often in association with Spongites fruticulosa; rarely also among Zostera rhizomes. Bathymetric distribution: littoral to lower sublittoral. Recorded up to 15-20m deep. Geographic distribution (Babbini & Bressan 1997):

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