I wonder if it’s the same chemical reaction as the bacteria use. Maybe they once had a symitoic relationship with the bacteria but just stole their reaction and eliminated the bugs. Or else just another of many instances of the same evolutionary feature pooping up more than once, i suppose.
Beautiful squid anyways.

There are several different biochemical pathways to bioluminescence. The marine phyla that exploit their own bioluminescence use a different pathway to bacteria. It appears that bioluminescence has evolved independently many times.

Interestingly, I think it unlikely that cephalopods “stole” the biochemistry from symbiotic bacteria. What tends to happen in evolution, as I understand it, is that when a symbiotic relationship sets up, both the host and the symbiont tend to lose those functions that the other does more efficiently. Eventually, in extreme cases such as eukaryotes (and that includes us), the host and the symbiont are so dependent on each other that they effectively become a single organism.

A good example to help explain this is that humans (and indeed all primates) have lost the ability to synthesise vitamin C. Most animals do it effortlessly. And in fact, primates still have the entire synthetic pathway encoded in our genes, but due to a mutation in one of the genes (which codes for an enzyme called L-gulano-gamma-lactone oxidase), the pathway doesn’t work. The obvious reason is that at some time in primate evolutionary history, the primate diet was so high in vitamin C that there was no need to synthesise it, and so when the pathway was damaged by mutation, there was very little selection pressure to weed out the mutation and it managed to work its way into the entire primate lineage. In this case, primates have effectively become long-distance symbionts of vitamin-C producing plants, and as a result our natural synthetic abilities have become vestigial. Likewise, if a squid adopts a bacterium that helps emit light, evolution would tend to push the squid (and the luminescent bacteria) into greater co-dependence.

As far as I know, swallowing code from symbionts and then dissolving the relationship is more commonly found in Microsoft than in nature.

Ha! Good one. I didn’t know that about vitamin C. I guess I was thinking of mitochondria, but that would be more like what you mention where two organisms effectively become one.