Architeuthis: How many hectos?

[Steve O'Shea]

I've been away for a few days, sorry.

I'd maintain absolutely no trace of hectocotylisation on any arm (I've not seen anything remotely 'hectocotylised' at any rate - certainly not comparable to that on other taxa for which the hectocotylus is very pronounced).

You'd have to be very careful when referring features found on both ventral arms to hectocotylisation.

 

[monty]

I've been away for a few days, sorry.

I'd maintain absolutely no trace of hectocotylisation on any arm (I've not seen anything remotely 'hectocotylised' at any rate - certainly not comparable to that on other taxa for which the hectocotylus is very pronounced).

You'd have to be very careful when referring features found on both ventral arms to hectocotylisation.

Does the sketch (figs G and G1) on p. 219 of Nesis not match your observations, then, or do you just consider that quirky arm anatomy (presumably sexually dimorphic as described)? It certainly looks, er, "groovy" in a classic hectocotylus style...



I note that the Roper & Sweeeney FAO guide also says "arms IV hectocotylized" but don't have a picture. I can't think of another ceph species that has 2 arms modified as hectocotyli, although there are plenty of non-hectocotylus sexual dimorphisms that show up on symmetric arm pairs, like enlarged suckers on GPOs and mercatoris... further googling suggests that there are a lot of species that match a search for "both arms hectocotylized" so I guess I'm just ignorant. But there seems to be some ambiguity when anatomists use the term whether the terms mean "sexually dimorphic characters of arms" or "arm is actually used to transfer spermatophores."

 

[DWhatley]

Monty,
My mercs have enlarged suckers on all eight arms and Sisturus has double enlargements (side by side) on all arms. Mucktopus' paper and a later Q&A described only 2 or 4 arms with the enlargements as typical on the various dwarf species. She also mentioned that the use is still unconfirmed.

 

[monty]

Monty,
My mercs have enlarged suckers on all eight arms and Sisturus has double enlargements (side by side) on all arms. Mucktopus' paper and a later Q&A described only 2 or 4 arms with the enlargements as typical on the various dwarf species. She also mentioned that the use is still unconfirmed.

Right, I meant that in most species, the sexually differentiated traits appear symmetrically on 2, 4, 6, or 8 arms, in pairs on opposite sides. The hectocotylus is a major exception to this, in that it's usually only a modification of one arm, and the one opposite it in the pair doesn't show the difference.

Do any of your mercs show modified suckers differently on the left and right sides of a single arm pair?

 

[DWhatley]

I guess humans are somewhat deviated this way too

 

[monty]

I guess humans are somewhat deviated this way too

"'Cause that's the hand I use... well, never mind." -- Simon & Garfunkel

 

[DWhatley]

Saw them in concert once

I tried to look at Sisturus' arms as matching or unmatching pairs but I think photos would be the only way to see if there is a pairing commonality as he really doesn't stay very still if I am sitting at the tank and his arms are not stretched out if he is just chilling on the glass. I am going to be devistated when this one goes. He is so much more like a bigger octo than most pygmies. If he dies the way Trapper did, I really won't be able to tell a lot about the suckers then either as her arms shrunk and weakened as she aged. So much so that I initially thought the suckers at the ends of her arms had been scraped or eaten off.

 

[Rick E]

Thank you. That answers my question.

 

[Rick E]

I figured my question would have a simple, black-and-white kind of answer; I didn't anticipate so many shades of grey.

 

[Steve O'Shea]

Does the sketch (figs G and G1) on p. 219 of Nesis not match your observations, then, or do you just consider that quirky arm anatomy (presumably sexually dimorphic as described)? It certainly looks, er, "groovy" in a classic hectocotylus style...

Thanks Adam. I've seen a few things like the illustrations in Nesis, but it's really hard to know whether these arms are damaged or not, as so often in trawl-caught specimens (the ones we deal with most often) the arm tips are incomplete.

I have had quite a number of mature males with one or two ventral arm tips complete, and have seen this condition in one or two specimens only (not in the majority), and never on both arms; I have also seen this condition on some other arms (not the ventral pair). I assumed it to be regeneration rather than hectocotylisation. I do not believe that absence of this 'condition' in some individuals (mature) means that there is more than one species (I believe there is one species only).

As Kat said earlier, those species that lack hectocotylisation 'as a rule' implant spermatophores in/on the female using their large 'terminal organ' (being a 'family show'), and given the 'enormous' size/length of this organ in Architeuthis I would be rather surprised to see any trace of modification of the ventral arms to assist in spermatophore transfer. The arms may be modified, but not necessarily for reproductive purposes, so we cannot assume any such modification represents hectocotylisation.

In response to some other query (sorry, I forgot who mentioned it), hectocotylisation of both ventral arms is very pronounced in some ommastrephids also (such as Nototodarus).