Not sure if this is the right spot to put this thread but is this what I think it is?
http://cgi.ebay.com/SEA-SHELLS-AND-SEA-LIFE-OCTOPUS-SPAWN_W0QQitemZ350044871075QQihZ022QQcat egoryZ71129QQssPageNameZWDVWQQrdZ1QQcmdZ ViewItem

That is intriguing.

If I had to guess, I'd say "sheep bladder." But what do I know? Any frequent-dissectors of octopuses recognize it?

I can't find the Steve Martin/ Bill Murray clip of "what the Hell is that thing" or I'd post it.

Copepod

Jellyfish?

They also have this for sale...

It's the ovary sac and oviducts of an octopus (of some description), but not from (above) Tremoctopus (the distal oviduct of this genus is exceedingly long and thin, and the eggs are minute - unlike the large eggs in the sac of the ovary for sale).

Why would anyone place the ovary & oviducts of an octopus on ebay? Rare? My word! What nonsense!

Wow. What a weird vendor. Seems they're shipping from Montevideo, Uruguay.

Also, what on earth is this thing? If they showed me the other side I might be able to guess, but...?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=350044867861&ssPageName=MERC_VI_RCRX_Pr4_PcY_BID_Stor es_IT&refitem=350044871075&itemcount=4&refwidgetloc=active_view_item&usedrule1=CrossSell_LogicX&refwidgettype=cross_promot_widget&_trksid=p284.m184&_trkparms=algo%3DCRX%26its%3DS%252BI%252 BSS%26itu%3DISS%252BUCI%252BSI%26otn%3D4

That's an isopod; looks liike a stomach content specimen though. Rare? Not! It's the kind of thing anyone from a museum would throw in the bin as it is completely worthless.

I want to call it Seriolis.... my memory is failing me; perhaps Acutiseriolis .... but can't find anything; go to the bottom of this link (http://pcwww.liv.ac.uk/earth/crozet/141205.htm) you'll see the live thing.

There's just nothing (almost) online about this beast, which makes me think I've got the name wrong (they are so common at ~ 1000m around New Zealand). I know there was a lass in Australia working on the group, and that she was changing all of the names around.

I think they still had giant isopods at the Long Beach aquarium when I went with marinebio_guy last fall...

http://biology.fullerton.edu/biol317/im/s03/ft2/ft14-24.html

Not sure what the exact species was, though, but large enough to give me "that looks like it should be in an Attack of the Giant Isopod" movie...

That's a living trilobite I tell you.

Well OK, maybe not. But I'd bet my copy of Whispering Grass on Serolis trilobitoides:

http://www.trilobites.info/triloimposters.htm