Another fun fact is that we often wrongfully call basically every sea slug a nudibranch. Nudis are from the Order Nudibranchia which doesnt contain sea hares, lettus sea slugs or even the 'blue velvet nudibranch'. The main thing to remember is that all nudibranchs eat sessile animals so you wont find any that eat algae or anything that moves for that matter. The book Marine Invertebrates by Ronald L Shimek PhD has a good section on them.
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