I have a question, sorry if it sound dumb, but all the research I've done on the subject keeps on leading me in two seperate directions, my question is: On the top of Spirula's mantle, is there a suction cup, or a light organ?

The fruits of my labor trying to find an answer turned up contradicting results, please help me out here.

:squid: I'm going to put this little guy here because he looks a little like a Spirula to me.

I've only ever read about a light organ being there.

What an interesting little animal, this Spirula.

There is a light-emitting organ at the and of its mantle but no suction cup. I wonder these little things and their shells were actually found...

Here's a Spirula shell from my collection of bits and pieces.

http://www.tonmo.com/phpBB/files/Spirula.JPG

The light organ is only visible from above as the animal swims vertically with the head hanging downwards. Most animals living in deep water do the opposite using lights aimed downwards to block out their silhouette to predators below. I wonder what the advantage of this arrangement is?

Wow, thanks guys, this is really helping out!

Strange having the light organ on top, below makes more sense as it would make the animal blend in with the ambient light from above.... I wonder if it helps break up the silouette???

J

Strange having the light organ on top, below makes more sense as it would make the animal blend in with the ambient light from above.... I wonder if it helps break up the silouette???

Really good point Jean. I'd been meaning to post on this thread for quite a while.

All the imagery I have seen of this animal is with the 'photophore' up, the head and arms vertical, oriented down. We actually kept Spirula live in the tanks for ~ 7 days, and this seemed to be its natural swimming orientation.

I've many individuals in the office and will take a few pics of the photophore very soon and post online. I've not seen it glow myself, and like everyone else had read and assumed it to be true that it was indeed a photophore. I'm in no position (at present) to comment otherwise.
Me

The light organ is most peculiar as it surely cannot act as a lure or camouflage. It has been reported that Spirula can glow for hours, so therefore its purpose seems quite bizarre and would possibly attract predators.
I'm aware that Spirula can control the intensity of the luminescence, but unsure whether it can totally extinguish it rapidly. I'm thinking it may be used for social communication purposes

Not sure if it would be relevant but what colour is the glow? Or can it be different colours? What depth do these normally live at?

"On several occasions we were able to perceive that the small bead-like organ at the posterior end is a light organ. It emits a pale, yellowish-greeen light, which from the normal position of the animal in water, is directed upwards... We have seen the light showing uninterruptedly for hours altogether" Schimdt (1922)

At least off the Canary Islands, they're generally found 500-800m+ during the day and they migrate to not much less than 150m during darkness.

Some kind of counter-shading? One could also conceive of it as a warning device (instead of the "fires" being lit to tell of approaching danger, they would be put out)? Dubious guesses at best though. :cyclops:

It's pointed in the wrong direction for countershading. Maybe it's to attract mates?