Colossal Squid Necropsy

[Steve O'Shea]

Re: Mesonychoteuthis anatomy

From Kat Bolstad's article on "Deep Sea Cephalopods" on this site, I learn that the gut of Architeuthis dux has a maximum relaxed diameter of only 10mm. Is the implication here that Architeuthis can only eat relatively small prey?

What is known about the gut of Mesonychoteuthis? Is it much wider in diameter than that of Architeuthis?

Is there any real evidence as to the lifespan of these large squids? I read somewhere that cephalopods as a whole seem to have short lifespans, and that a very rapid growth rate is thereby implied for Architeuthis. What about Mesonychoteuthis?

There is a general rule that prey species are shorter-lived, and much more fecund, than their predators. It has been reported that the Patagonian Toothfish, which seems to be a very long-lived species, is a major part of the diet of Mesonychoteuthis. This might indicate that Meso. has a considerably longer basic life span than is typical for cephalopods.

Hi Frank. That's a rather interesting post. The oesophagus of Architeuthis and Mesonychoteuthis is of comparable diameter, in that it is narrow in both (10-15mm). Both squid eat prey larger than this greatest dimension, but the prey is chopped up into quite small pieces by the beaks and (theoretically) further masticated by the radula (although the radula doesn't really seem to play a major role in chopping the prey up, in that squid flesh in the gut of Architeuthis isn't scoured by the radular teeth).

Sitting atop the computer right now is one of the two statoliths from the Mesonychoteuthis squid. It is tiny (~ 2mm greatest dimension); Mesonychoteuthis would appear to be a pelagic squid (benthopelagic and benthic forms, as a rule, have larger (relatively speaking) statoliths). By sectioning this tiny statolith (something we'll leave to George Jackson, Hobart) we'll be able to count tiny rings (much like those seen in section of a tree trunk). It is assumed that these rings are deposited on a daily basis, but this has not been validated for cold-water deep-sea species of squid. We're attempting validation now (it has been validated for shallow-water tropical species). So, at this point, we'd be uncomfortable estimating age.

Your third point, the relative life spans of predator and prey, is most interesting. The smaller Mesonychoteuthis are eaten by larger Patagonian Toothfish, so it could become a circular argument. But this is definitely worthy of further consideration; consider it filed in the back of the head - we'll look into this.
Kindest
Steve

 

[frank h.]

Re: Mesonychoteuthis anatomy

Steve, many thanks for your informative reply to my queries. Like so many others, I look forward with interest to more reports from yourself and Kat, as you further study these fascinating creatures.

I gather that you are tending to believe that Architeuthis is a largely "passive" predator - and therefore of little "danger" - whereas Mesonychoteuthis is powerful, aggressive, and formidable.

Some shark analogies come to mind. Architeuthis is perhaps a sort of squid equivalent of the Megamouth, Basking, and Whale sharks, even more so of the mysterious Goblin Shark (Mitsukurina) which is also benthopelagic or benthic. On the other hand, Mesonychoteuthis is a Great White or a Tiger!

I must admit to a tinge of sadness that Architeuthis has lost its status as the scariest cephalopod. This reminds me of the recent discoveries of meat-eating dinosaurs larger and more formidable than Tyrannosaurus. Actually the scientific name 'Architeuthis dux' is entirely comparable to 'Tyrannosaurus rex'. Was one named in analogy to the other?

The smaller Mesonychoteuthis are eaten by larger Patagonian Toothfish, so it could become a circular argument.

The Patagonian Toothfish itself seems to be quite an imposing creature, for a bony fish.

Among other things, I look forward to further report on the eyes of Mesonychoteuthis. Cephalopod eyes are especially interesting of course, partly because of their remarkable similarity to vertebrate eyes - indeed in one respect, the arrangement of the retinal cells, they are, at least theoretically, slightly more efficient than vert. eyes. And because of their similarity to our own, ceph. eyes have an "emotional" impact on us, which the very different eyes of insects can never have - note how cartoon films such as "Antz" give the insects vert./ceph. type eyes.

Regards and best wishes

Frank

 

[frank h.]

Re: Mesonychoteuthis anatomy

Thanks, WhiteKiboko, for your reply.

I too am very far from being an expert!

[I'd love to visit NC sometime and attend a college football or basketball game involving UNC, Duke, or NCState ]

Regards

Frank

 

[tonmo]

The analogy, "Architeuthis is to a basking shark as Mesonychoteuthis is to a great white" is an interesting one.

Of course, great whites have been largely defined for the general population by the movie Jaws, for better or for worse... Well, ok, probably for worse. Also, the summer of 2001 saw a number of sensational shark attacks that received tons of press here in the US, and probably elsewhere.

Luckily, it would seem a Mesonychoteuthis attack on a beach-goer in 3 feet of water is about as likely as a gorilla attacking a spectator at a hockey game. Hey, how's that for an analogy?

Anyway, back to YOUR far better analogy... you were of course comparing their generally aggressive natures, not necessarily their propensity to attack humans. The thought of Architeuthis as a relatively mellow creature is fascinating.

I tried to search through some of Steve and Kat's earlier posts on Architeuthis aggressiveness, but didn't find anything that went into further depth (although I may have not been using the right search terms). Would be interested in any thoughts or speculation in this area?

 

[Fujisawas Sake]

Steve and Kat,

Congratulations, and I hope to read more about your discoveries... Your description of the anatomy was... odd... I'll admit, you have my attention.

Sorry that I've been away, but needed to take a self-imposed exile to Texas... Will have to return soon.

Sushi and Sake,

John

 

[Steve O'Shea]

This should have aired on Discovery Channel News (Canada) a week-or-so ago; we've yet to receive copies so don't know what the final product looked like.

Cheers
Us

 

[Bald Evil]

Steve talks like Phantom...Ghost Who Walks...the Marine Biologist Who Cannot Die...

So much for your secret identity!

 

[Steve O'Shea]

I am but a figment of your imagination. My real name is Paul.

 

[myopsida]

will paul come back as superman?

 

[tonmo]

Has anyone seen this documentary, perchance?

 

[myopsida]

No, but I saw Steve the other day - almost as good as the real thing!

 

[Steve O'Shea]

Paul will be in Wellington again in a couple of weeks to check out the flounder collections; will make it for a Friday bev. ; I'll be the one in the red lycra suit. Gotta check out those cranchiid collections to see whether there's any juvenile Mesonychoteuthis from NZ/proxim waters, and octopoteuthid collections to finish off two more MS's. Both are proving to be real cans of worms.

 

[Steve O'Shea]

Can either Steve or Kat tell me? Is the inner mantle really black?? Or was it ink? or an artifact of filming? J

A frightening thing just occurred to me (have just woken up, so must have been thinking about this). The standard theory is that the inner wall of the mantle is dark, in the case of Mesonychoteuthis, black, to shield light from bioluminescent prey in the squid's stomach/stomach caecum from shining through the mantle, identifying the squid to potential predators.

Other than the sperm whale (I'm not sure whether the whale uses eyesight or sonar to locate prey), what possible predator could there be down there that would take on a full-grown colossal squid?

There must be another reason for the dark-pigmented inner-mantle wall of the colossal squid (it is this or there is something even more formidable down there ..... shudder!). Prey (as in Patagonian Toothfish), don't bioluminesce (as far as I know), so the dark inner-mantle wall probably doesn't serve to conceal the squid from potential prey .....

Something weird is going on. Anyone with any suggestions?

 

[Steve O'Shea]

Having given this 2 coffee's worth of consideration I have come up with 2 suggestions:

1) Cranchiid squid like Teuthowenia can pull their head entirely within their mantle, inking within the mantle and appearing like grapes (this is actually what I thought we had in one sample several years ago - deep-sea 'grapes'). As the eyes of Mesonychoteuthis have photophores, perhaps this animal can also withdraw the head (and arms) within the mantle ... ouch ... and the black lining of the mantle wall conceals any bioluminescence from the eyes. You still have to have a large-enough predator to warrant this behaviour, however. Perhaps the smaller animals need to be able to do so, and the character state is just carried forth through to the adult (where it isn't really required, but is a non-lethal behavioural attribute ... as in it doesn't harm the animal to be able to do so, rather than it being advantageous to be able to do so).

2) The ink is bioluminescent .... and for the same reasons as above, this character state is retained by the adult, and is a non-lethal condition.

Any further suggestions?

 

[Clem]

Steve,

Don't know how effective head retraction would be in eliminating the light signature from the photophores, but I don't know what Mesonychoteuthis' orientation in the water column might be (I'm waiting on "the theory"). Unless the seal between head and mantle was very tight, you'd still see a cylindrical shaft of light emanating from around the retracted head. If Mesonycho held its head down, that leakage would probably not draw diving predators, but...I'd also worry about damage to the eyes incurred during a fast, emergency retraction. Ouch is right.

I'd think that cupping the eye with a looped tentacle would be about as effective at masking the ocular light organs. Can Mesonycho stretch its arms and inter-arm web up high enough to hide the eyes, ala Vampyro?

If the "stealth lining" theory is correct, perhaps it was most useful back when there were 12-meter, apex-predator sharks to worry about.



Clem