April 2013 – A nudibranch eating nudibranch – this one gives me the heebie jeebies. I know many divers who go crazy over nudibranchs the way we go crazy for blennies. Nudibranchs belong to the phylum Mollusca and share a subclass, Opisthobranchia, commonly called sea slugs. Many are beautifully colored and some are very cryptic, mimicking the things they feed upon, like coral or sponges. Brightly colored nudibranchs really stand out to us in the muck or rubble bottoms that we like to explore but a nudibranch with a tiny pigmented eyespot and unrefined optic nerve can’t see in the sense that we do – it is believed that they rely on their sense of smell through their rhinophores, the organs on top of their heads.
During a dive on a particularly silty mud bottom in Batanta, Indonesia, I was concentrating on a colorful Gymnodoris nudibranch, a fairly large species known to be a predator of other nudibranchs. I didn’t notice the smaller Hypselodoris approaching until I heard our guide calling through his regulator. About the time that I realized it was there, the Gymnodoris sensed the smaller nudibranch and grabbed it. The Hypselodoris escaped. That prey and predator could not see each other was apparent during the next ten minutes as the Hypselodoris was pursued and finally consumed. I’ve edited the video down to around three minutes; watch it below or visit our BlennyWatcher YouTube channel: