A small, thin, flattened oyster that grows clamped along the branch of a gorgonian or a sea whip rather than on rock, with the lower valve molded into a groove around the stem it settled on. The species name folium means leaf, for the flattened leaf-like shell. Margins are scalloped into small regular folds, and color ranges from reddish and purple to dull brown, frequently matching the host branch closely enough to be missed at a glance. Length reaches about 7 cm (2.8 in).
Sitting up in the water column on a host branch puts the animal directly in the current, which suits a filter feeder: it strains plankton and suspended organic matter from water that is already moving past. Several individuals commonly line up along a single gorgonian, spaced out along the branch. It occurs on reef slopes and drop-offs where sea fans are abundant, from about 1 m down to 30 m (100 ft), and is among the easiest small oysters to find in the 🌊 Red Sea simply because its hosts are conspicuous. Empty valves stay locked onto dead gorgonian skeletons long after the animal has gone.
- clamped along a gorgonian branch, molded around it
- margin scalloped into small regular folds
- shell thin, flattened, often reddish or purple
