Sabella spallanzanii is a species of marine polychaete worms in the family Sabellidae. Common names include the Mediterranean fanworm. It is native to shallow waters in the northeastern Atlantic Ocean and the Mediterranean Sea. It has spread to various other parts of the world and is included on the Global Invasive Species Database. The species’ name commemorates the 18th-century biologist Lazzaro Spallanzani. European fan worms grow to a total length of 9 to 40 cm and are usually larger in deep water. They have stiff, sandy tubes formed from hardened mucus secreted by the worm which protrude from the sand, and a two-layered crown of feeding tentacles which can be retracted into the tube. One of the layers forms a distinct spiral. The colour of the tentacles is variable but they are usually banded in orange, purple and white or they may be a uniform pale grey. Various epiphytic organisms settle and grow on the tubes which may be rather wrinkled near their bases. It is found at depths down to 30 m (98 ft) and is found in nutrient-rich waters in sheltered locations where there are no strong currents and little wave action. It grows on soft sediments or anchors itself to rocks, mollusc shells, jetties, pontoons or other solid surfaces. It may grow on the hulls of moored boats but does not usually foul vessels that are in frequent use.