Aspect: Thin white-tufted parallel branches alternately growing in a single plane on either side of a small brown stem. The white tufts actually are polyps that also extend alternately upwards and downwards from each branch. Taller specimens (about 15cm max), may carry secondary branches. ATTENTION: formerly Sertutella speciosa, now Serturella diaphana Population: Common, especially on current-swept natural bases or man-made structures, like mooring jetties and shipwrecks which they can generously invade, and particularly around wreck window and doorframes that offer a good flow of plankton-rich currents, but also permanent mooring lines. Notable feature: The tiny white horn-shaped polyps are home to about 28 hair-thin tentacles in charge of catching plankton. Environment: See "population" above. Behaviour: Stings badly, not to be touched.