I find animals (and heterotrophic organisms in general) to be distinctly upsetting. This sometimes confuses or disturbs people, but don’t get me wrong, I think animals have a right to exist and all that. I just don’t love the whole “eating other sentient creatures” bit.

Sometimes I find an animal interesting despite my reservations. This is usually because of a bacterial symbiosis of particular interest.

The Hawaiian Bobtail Squid is one such animal. They are very small (roughly 30 mm in length, weighing less than 3g.) and eat animals even smaller than them. Mostly krill and various tiny crustaceans.

This, however, poses a problem for the humble squid. They are so very small and edible without much means for defense.

To manage this problem, the squid lives nocturnally and employs the camouflage strategy of counter-illumination. Essentially, under ideal conditions, the light blends in with the light of the background. They hide beneath veils of false moonlight.

The interesting part to my bacterially addled mind is the light organ. If raised in sterile lab conditions however, the squid never develop this organ beyond a basal, inactive state. They need to be exposed to the Aliivibrio fischeri (prev. known as vibrio fischeri) ubiquitous in their marine habitat.

The squid secrete a special biochemical mucus when exposed to peptidoglycan, a component of cell walls. Bacteria inundate it, and for reasons yet unclear A. fischeri outcompetes the others. It has very strong flagella, so it can swim through the thick mucus and enter the nascent light organ (which appears at that point as an undeveloped eye). As they continue they go through a sort of biochemical-mechanical series of trials selecting for A. fischeri much like the Nerevarine in the Ashlands.

In particular the squid make a peroxidase which, in tandem with peroxide, shreds most microbes by utilizing the fell power of oxygen. A. fischeri, however, produce a catalase in the periplasm. It yoinks the peroxide before the squid can, disarming the swimming pool of live grenades they find themselves navigating.

The bacteria finally make it to the antechamber of the organ and colonize its six (immaculately named) crypts. At this point, mere hours after the squid hatch, the organ is active.

The bacteria make the light via a typical luciferin-luciferase system, and in turn the squid feeds them sugar and amino acids. At dawn, the squid jettisons like 95% of them while it rests in the sand and does it all over again next night.

In short: The bacteria are the source of the light (and the squid is just what we see) and the peroxidase is a gatekeeping blaze that lies quiet in offering to Alii-v.