[Fishbowl, 50 fsw., Photo © 1995, A. Kimo Morris.]

Nudibranchs (also called sea slugs) are always fun to find. Many nudis are "cryptobiotic" (camouflaged to resemble the background) in order to hide from predators. Other nudis utylize a different strategy for avoiding being eaten. For example, the nudibranch on the left (Pteraeolidia ianthina ) is highly conspicuous. This nudi feed on certain stinging hydroids and is able to pass the stinging cells (nematocysts) through its gut and encorporate them in its tissues where they provide protection from potential predators. They can even induce a mild reaction in humans. From its food source, this nudi also accumulate zooxanthellae, a unicellular algae that is capable of photosynthesis. Thus, the algae can provide some nutrients to their nudibranch host, clearly a mutualistic relationship.