Photo via jon hanson @ flickr
Slugs as we know them aren't the most colorful land-based creatures, but the shell-less mollusk known as nudibranchs (meaning "naked gills"), or sea slugs, are the complete opposite: The more than 3,000 different members of this species are each entirely different. In most cases, their brilliant colors come from the food they eat--and do double duty as a protective feature: Some slugs are poisonous, and some aren't, but what kind of predator would want to take the chance? The neon colors are a clear warning. Click through to see some of the most intensely-hued slugs the water has to offer.
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