Anything is possible 'ey.
No it's not,
Run 50 kilometers in under 30 seconds. Then I will believe that anything is possible.
or
Hold your breath constantly for two days, I will accept that too.
or
Jump over the Moon in a single jump - just like the cow

I will accept that too.
The Coelacanth is a great deal smaller than a proposed Sea Serpent, how is it you reckon we have missed the Sea Serpents, but picked up on a fish? The Coelacanth was discovered in 1938 - fair while ago. Our technology and presence on this planet has increased greatly since that time as well.
Just strikes me as strange that some divers on holiday can find a 6 inch Lobster at a depth of 7,540 feet of the coast of an uninhabited island 900 miles from anywhere - now you really have to be suitably impressed by that or you are just not thinking rationally. Yet we don't have one clear undeniable picture or piece of irrefutable evidence of a Sea Serpent wich enjoys many reported public sightings each year......

So what is going on? How is it these creatures are better at camoflage than a chameleon - we have found those and they are pretty darn small. Octopii are pretty adept at is as well, yet we have found quite a few of them some really small ones too.
Yeah the Ocean is a big place, and yeah there is heaps to learn yet. I don't think it is likely at all that we will find something so brand new and of such impressive proportion to add to our animal library though. It is not like we have discovered something the size of a Whale even in the last 100 years.
For those who believe they exist, why do you believe? I would be really interested to know what has you so convinced?
(geez - seen the silly names already being used by some for the new crustecean - Yeti Crab, Bigfoot Lobster, that just sounds sooooo stupid

)