One group of creatures they observed - and captured - during their six weeks in the Atlantic aboard the RRS James Cook is believed to be close to the missing evolutionary link between backboned and invertebrate animals.
Using the latest technology they also saw species in abundance that until now had been considered rare.
Researchers were also surprised to discover such diversity in habitat and marine life in locations just a few miles apart.
Scientists were completing the last leg of MAR-ECO - an international research programme, part of the Census of Marine Life, which is enhancing our understanding of the occurrence, distribution and ecology of animals along the Mid-Atlantic Ridge between Iceland and the Azores.
The University of Aberdeen is leading the UK contribution to the project which involves scientists from 16 nations. Key collaborators in the UK include Newcastle University and the National Oceanography Centre.
During more than 300 hours of diving - using Isis the UK's deepest diving remotely operated vehicle (ROV) to depths of between 700m right down to 3,600m - researchers surveyed flat plains, cliff faces and slopes of the giant mountain range that divides the Atlantic Ocean into two halves, east and west.
The research was focused in two areas - beneath the cold waters north of the Gulf Stream and the warmer waters to the south.
Professor Monty Priede, Director of the University of Aberdeen's Oceanlab, said: "We were surprised at how different the animals were on either side of the ridge which is just tens of miles apart.
"In the west the cliffs faced east and in the east the cliffs faced west. The terrain looked the same, mirror images of each other, but that is where the similarity ended. It seemed like we were in a scene from Alice Through the Looking Glass.
"In the north-east, sea urchins were dominant on the flat plains and the cliffs were colourful and rich with sponges, corals and other life."
New Deep Sea Species Uncovered
GENERAL - Scientists have just returned from a voyage with samples of rare animals and more than 10 possible new species in a trip which they say has revolutionised their thinking about deep-sea life in the Atlantic Ocean.