“Air Fern” (Serularia argentea)
…although it may look like a plant S. argentea is a species of hydrozoan that occurs throughout the North Sea. Like other hydrozoans S. argentea is a colonial animal consisting of multiple animals known as zooids. Like other cnidarians S. argentea likely feeds on small microorganisms which are dispatched via stinging nematocysts.
S. argentea is often sold commercially as a ‘decorative plant’ or as an aquarium item. Despite its resemblance to a plant as mentioned before air ferns are animals and are sold as calcium carbonate 'skeletons’.