From a morphological perspective, these sea slugs might seem quite similar to the sea cucumber. However, they couldn’t be more different. These are actually molluscs that have shed or are in the process of losing their shell. Additionally, their food source is quite different from the sea cucumbers, or any of the marine inhabitants for that matter. Nudibranchs, mainly the Aeolidiidae, feed on the phyllum cnidaria (Farley 2017), which entails animals such as sea anemones and jellyfish, known for their defensive strategy using nematocysts. Nudibranchs have this amazing adaptation that allows them to ingest and digest cnidarians without getting hurt from the released nomatocysts. Even more impressively, they can single out these nomatocysts in the digestive process and bring them into their own tissue to use as their defensive strategy (Schlesinger et al 2009).
Figure 1: Illustration of Nudibranch anatomy highlighting the organs devoted to kleptonidae adaptation (Illustration credit: Sara Mynott)
This kleptomaniac adaptation is brilliant, it means that what energy and time was spent on evolving these specific adaptations could be spent on a generalist approach to steal other species specialization. By generalist approach I mean that not only can Nudibranchs steal nomatocysts, they can also cross over trophic levels by stealing chloroplasts, thereby turning into primary producers (McFarland & Muller-Parker 1993). Consider how incredible that could be for you if you had that adaptation, you had only to eat some plant tissue and then you would be able to produce your own energy with the power of sunshine. So the question is, can we evolve this kleptonidae adapation? Also, can I please have it. To start answering that question we have to understand where this adaptation came from.
The first thing that comes to mind is the similarity with the endosymbiotic theory that explained the evolution of eukaryotic cells from prokaryotic organisms. However, this theory postulates that two prokaryotic cells combined where the smaller evolved into complex organelles such as the mitochondria and chloroplasts (The editors of the American heritage dictionaries 2015). Whereas kleptonidea revolves around the one absorbing the other, intentionally. Additionally, that these are multicellular organisms, in contrast to the procaryotic organims, which severly complicates things.
In all, what scientific literature I have found on the Nudibrnachs and kleptonidea has not given any further insight into the evolutionary pathway of the adaptation. Nor did I find any research into the selective digestion or the adaptation of utilizing something digested for protection or divesting from predation. However, I did find that certain flatworms have a similar adaptation of kleptonidae towards nematocysts (Greenwood 2009). And as these species are within a seperate phyllum, this means that this adaptation has evolved twice. Which is quite rare in itself, but with the added rareness of the adaptation in question, it makes the whole thing so extremely rare. I am both surprised and frustrated that this has yet to be researched further and promptly urge all biologists to get on with it.
To calm your nerves, if you got frustrated by the bottomless pit of no answer like me, have a look at this incredible assortment of Nudibranchs to a calming melody.
Next week I will talk about a surprising adaptation found in Parrot fish.