Acetabularia dentata

Thallus small, to 2 cm high, rarely solitary, mostly gregarious, umbrella-like shaped, green to light bluish-green, heavily calcified. Disc solitary, flat, shallow-dish shaped, (capshaped in young plants), (1)-2-5 mm diam., of 18-30(-38) clavate rays. Outer margin of ray rounded or truncate with central tooth. Corona superior consisting of irregularly rectangular coronal segments at base of each ray on the upper surface of the disc, 100-110(-120) mm long, 40-55 mm wide, with 2-3(-4) hair scars in uniseriate rows. Corona inferior with coronal segments, 62-70 mm long, 48-55 mm wide with outer deeply emarginated or bilobed margins (rarely trilobed). Gametangia are mature rays; cysts spherical 75-85(-100) mm diam. Stipe 280-400 mm diam., 0.4-1.2 cm high, heavily calcified. Attachment by small, inconspicuous holdfast. Growing on hard substrates, often on dead coral fragments at shallow calm sites.

In subtropics and tropics of Pacific Ocean.