Nudibranch Evolution

[Theophrastus]

For various reasons, (whether for medical research, or their elusiveness) nudibranchs, have quite recently become the subject of much attention. Now I know that nudibranchs are of course related to gastropods, but have evolved in various ways, and after millions of years, they differ drastically from their gastropod relatives. One fundamental difference is the lack of a shell. Nudibranchs, instead protect themselves from predators by means of toxic secretions. What interests me is that these toxins are not produced within the body, but rather, extracted from their prey.

All of these things tie into my area of question. Does anyone know at about what time evolution resulted in the rejection of the shell, and accordingly, for what reasons could this have occured, despite the shell's obvious beneficial, defensive function?

Secondly, I'ld also like to know any additional information on how nudibranchs converted their digestive systems, in order to be capable of extracting key chemical toxins, from other aquatic flora and fauna, and then proceeded to store them.

Any helpful responses, would be appreciated.

Edited July 6, 2009 by Theophrastus
addition of content.

[Mokele]

For various reasons, (whether for medical research, or their elusiveness) nudibranchs, have quite recently become the subject of much attention.

 

It's mostly Aplysia, the 'sea hare', because of its simple nervous system and the fact that its ink reflex involves electrical synapses (rather than chemical ones).

 

Now I know that nudibranchs are of course related to gastropods

 

Technically, they're a type of gastropod.

 

What interests me is that these toxins are not produced within the body, but rather, extracted from their prey.

 

This is actually quite common. For instance, the famous poison dart frogs of South America (and their convergent cousins, the Madagascan mantellas) acquire their toxins from the ants and beetles they eat. Monarch butterflies are toxic due to the plants they eat as caterpillars.

 

All of these things tie into my area of question. Does anyone know at about what time evolution resulted in the rejection of the shell, and accordingly, for what reasons could this have occured, despite the shell's obvious beneficial, defensive function?

 

I can't find anything about the age of the particular group, but there is actually a general trend towards shell reduction within the Opisthobranchia. Speculating, I'd say that some species have lost it in order to fit into tight crevices, while others have lost it in order to increase mobility (many nudibranchs are active swimmers, something impossible with the massive shell of most snails).

 

Secondly, I'ld also like to know any additional information on how nudibranchs converted their digestive systems, in order to be capable of extracting key chemical toxins, from other aquatic flora and fauna, and then proceeded to store them.

 

Not a clue, sorry. Even weirder is that they can ingest and process nematocysts without triggering them.

 

Mokele

[Theophrastus]

Thanks for all the awesome input mokele! In particular, in regards to the evolutionary tendency within Opisthobranchia, of shell reduction; that is something I shall gladly add to my notes. It's also odd, because I always considered nudibranchs to have their own suborder, but it seems, from some of the research I've done following your notice, that the fact has long been reprimmanded. I suppose it serves me right for using an outdated text.

 

As for the "sea hare," I'ld actually heard not too long ago, that one compound it produces was actually thought to be capable of treating cancer. It made it all the way to clinical tests, however, it sadly failed.

 

I also looked further after you mentioned the nematocysts (a name that I have never heard of before), and my obvious question is- has there been any conclusive research into how nudibranchs can digest and process them, without any harm, or if that leads to nothing, what chemicals result in nematocysts' destructive capabilities. (As this by nature could hint towards a possible inhibitor, within the nudibranch)

 

In regards to the relative time of this change, this I would still like to know as it can give further insight into why the change occured (however I certainly agree that the desire for increased mobility and versatility is a part of it). For example, mammalian evolution, really picked up the pace, following the extinction of the dinosaurs (If I remember correctly). In a similar fashion, the circumstances of the time, could dictate the relevant necessities of the animal. Thanks again for the insight, any further help in general from the rest of the community, would be most appreciated!

 

"Sunshine, lollipops and rainbows!" (I'm not quite good with endings)

 

Theo

Edited July 7, 2009 by Theophrastus
grammatical mishaps