starfish

English starfish is a compound of star and fish, first attested in the 1530s. The name is descriptively wrong — the animal is not a fish. It has no spine, no gills, no fins. It moves on hundreds of tiny tube feet using a water vascular system unique to echinoderms. But the name made sense to the people who coined it: a star-shaped creature found in the sea. 'Sea-fish' was the category, 'star' was the shape.

The scientific community has increasingly preferred 'sea star' since the 1960s, arguing that calling a non-fish a 'fish' causes taxonomic confusion. The shift has been only partially successful. Marine biologists say 'sea star.' Everyone else says 'starfish.' The popular name has proven resistant to correction, the way it always does.

Sea stars can regenerate lost arms. The common sea star (Asterias rubens) can regrow an arm in about a year. Some species can regenerate an entire body from a single arm, as long as part of the central disc is attached. Oyster farmers in the 19th century tried to kill sea stars by chopping them up and throwing them back. The pieces regenerated. The pest multiplied.

The crown-of-thorns starfish (Acanthaster planci) is one of the largest and most destructive coral predators. Outbreaks on the Great Barrier Reef — triggered by agricultural runoff that feeds the larvae — have destroyed vast sections of reef. The animal named for its beauty is, in ecological terms, a coral-eating machine. The star at the bottom of the ocean is not always benign.