Looks like the species "Sewagicus Polluticus Mutationus".
Funny how we now play 'God' and create species anew by our own ...device.
You should see the 'strange' chickens that we hatch from the Hatchery where I work. Many, but not a majority, have extra legs protrude from their anus or stomach. They are alive. Then there are the ones that just stare upwards neurotically with blinking twitches.

I can't remember specifically, but there was a report of animals finding it hard to mate with their own species due to a severe 'lack of', that they are going for other/similar species and cross-breeds/retardations are being born.

Ever see

River

Monsters

on ABC TV?

 I think it's one of them.

 Moreover, it seems to be a baby extinct ichthyosaur.



 I'd be contacting the Smithsonian instead of the museum.  

---

 No, curiously, coincidentially in the manner normally reserved for  cryptozooological matters, I just saw the episode last night on Sawfish which are very rare now, and Jeremy Wade went to Australia to catch one.

 Yours seems to have teeth (though probably doesn't); the pipe fish doesn't. They don't have an exo-skeleton like prawns, but he said have very tough skin. And missing the tail as you said, which is like a shark - on both other creatures. Darn.  

Maybe that's a hybrid prawn