I discovered today that sea urchins (echinoidea) are known as zee-egels (sea hedgehogs) in Dutch, and that they used to be known as sea hedgehogs in English as well. They have similar names in other languages, for example, in German they are Seeigel (sea hedgehogs), in French they are oursins or hérissons de mer (sea hedgehogs) and in Spanish they are erizos de mar (sea hedgehogs).

The word urchin comes from the Middle English word yrichon (hedgehog), from the Old North French word *irechon, from the Old French herichun (hedgehog) – in Modern French hedgehog is hérisson – from the Vulgar Latin *hericionem, from the Latin ericius (hedgehog), from the Proto-Indo-European root *ghers- (to stiffen, bristle, stand out). From the same root we also get such English words as gorse, hirsute, horror and ordure.

The word urchin is apparently still used for hedgehog in some English dialects such as Cumbria, Yorkshire and Shropshire. It came to refer to people who looked or acted like hedgehogs from the early 16th century, and to poor, ragged youths from the mid 16th century, though this usage didn’t really take off until the late 18th century. Sea urchin was first used in the late 16th century.

Sources: Online Etymology Dictionary and Indo-European Lexicon