Fig. 1.  Nudibranch Peltodoris nobilis within the tentacles of an anemone Anthopleura artemisia.  Apologies for the blurry photo:  this tiny screen-grab was the best that could be done owing to the online inaccessibility of the journal and the authors themselves, who were asked for the original image but did not respond

Courtesy The Southwestern Naturalist

Fig. 2.  Nudibranch Peltodoris nobilis being nibbled by a garibaldi Hypsypops rubicundus.  This damselfish species is reporrted to prey on nudibranchs, but note the lack of savagery in the "attack"

Courtesy Kevin Lee, Fullerton, California

As can be seen from the above list, the defensive repertoire of nudibranchs and their relatives (Opisthobranchia) is extremely strong, and is unmatched in scope by any other marine invertebrate taxon.  In face of such defenses, it is not surprising that predators are scarce or absent.  Examples of supposed predation are described below.

Two researchers  from Pacific Union College, California witnessed a nudibranch Peltodoris nobilis apparently being consumed by an anemone Anthopleura artemisia (Fig. 1).  The authors did not see the outcome, but the interaction is interesting nonetheless.  A second example of "predation" on Peltodoris nobilis, in this case by a garibaldi fish Hypsypops rubicundus. is shown in Fig. 2.  Predation on nudibranchs is so unusual as to be essentially non-existent, likely owing to their impressive defenses.  So, it is quite likely that what we see here are simply happenstance and not examples of an evolved predator-prey relationship.