Acetabularia:

Genus composed of a slender, usually calcified stipe that terminates in a concave or flattened disc.

Acetabularia crenulata:

Morphology: thin stalk arising from a lobed rhizoidal base, with parasol shaped cap composed of a whorl of finger-like branchlets. Species up to 8 cm tall with discs 5-8 mm in diameter, single or layered one upon the other composed of a whirl of radiating segments or filaments originating from the stipe, sometimes with an additional whirl of smaller radiating segments above and below the main disc;partly or completely calcified, may appear white.

Frequently overlooked but nonetheless widely distributed, this species is most commonly found in shallow quiet waters attached to stones, rocks, shells and other submerged objects. Found year round.