genus with single or multiple fan-shaped blades, splitting
when larger or older; margin generally involute or rolled in; blades 2
to several cells thick; zoned with moderate to heavy rows of microscopic
hairs; calcium carbonate commonly over one or both surfaces of blade.
Species producing clusters of fan-shaped blades that are entire, split or segmented; calcification on upper surface, light to none below; blades 2 to 8 cell layers thick.
Common on rocks below the low tide zone; often partially
or totally covered with fine sediment; year round; abundant during warmer