Mer Creatures are around 4.5 metres long and 2 metres tall. The Mer seem intelligent, by locking up their human prisoners in a sewer, which acts like a pantry. Mer seem to have a society ruled by one large, red "MerQueen", with the other, much smaller animals acting as her subordinates. The MerQueen displays similarities to elephant seals, as she (perhaps accidentally) crushes other Mer while trying to get to her enemies. The elephant seal, a type of huge amphibious sea mammal, does this when fighting rivals for mating.
The Mer did not at any point kill any of their supposed victims, showing this may have been a way of keeping their prey fresh to eat in harder times. At one point, the MerQueen tried to grab Abby Maitland, although Abby must have escaped through the Anomaly. When she was found, she was not near the MerQueen, and was unharmed. Only when the team tried to rescue her did the MerQueen react aggressively by charging at the team. (Episode 2.4)
The Mer Creatures appear to have very weak skulls, as Connor Temple and Lucien Hope were able to kill Mer, or at least knock them out, by dropping heavy objects on their heads. (Episode 2.4) Despite this, one Mer Creature was seen ramming its head against a door in Oliver Leek's Creature Prison with no apparent damage done to it. (Episode 2.7)
It is unknown how or when the Mer evolved, though they presumably evolved from a primate that became aquatic. Nick Cutter theorised that the Mer could be Humanity's future descendants.
Several Mer Creatures came through an Anomaly from a shoreline, into a warehouse in the present day. The Anomaly then closed behind the Mer seconds afterwards.
Some Mer Creatures travelled through the warehouse's pipes into a canal in the Isle of Dogs. The Mer also made a base in the warehouse, which had partially flooded. The Mer Creatures captured Lucien Hope through a drain, then later Abby Maitland in a canal when Nick Cutter tried to draw the Mer out with a recording of their song. The Mer took both Abby and Lucien back to the warehouse and kept them in a flooded tank.
When Cutter, Connor Temple and Stephen Hart discovered the Mer's lair in the warehouse, they freed Lucien and were attacked by the Mer Creatures before Stephen gunned most of them down. Abby, meanwhile, was taken by the MerQueen back into the future when the Anomaly reopened, causing the team to go through after her. In the future, when Abby tried to escape the MerQueen with Connor's help, the MerQueen and several other Mer Creatures launched an attack. However, Connor managed to kill one Mer Creature by dropping a rock on its head, the others were brushed aside and possibly killed by the MerQueen, and the MerQueen itself was gunned down by Cutter and Stephen.
Two Mer Creatures were captured by Oliver Leek and kept captive in his Creature Prison as part of Leek's A Mer trying to escape Leek's Creature Prison. (Episode 2.7)
creature army. They escaped along with the other creatures when a computer virus disabled the security system, and tried to escape the bunker. The Mer returned to the cage room when they heard the siren for food, and were locked inside with Stephen. The Mer Creatures were presumably killed when the trapped creatures turned on and destroyed each other.
Like the Future Predator, the Mer is likely to have been inspired by Dougal Dixon's book After Man: A Zoology of the Future. In the book, set 50 million years in the future, primates have evolved into several new forms and one of them has adapted to swim and catch fish in the waters of tropical rivers. A further evolution of this "swimming monkey" might turn it into a seal-like creature similar to the Mer.
Nick's joking comment about the Mer being a possible descendant of humans is a reference to the satire novel Galápagos, by Kurt Vonnegut.
Due to the Mer's resemblance to Mermaids and Mermen because of their tails and vaguely humanoid shapes, some fans believe that the Mer could have come through the Anomalies to earlier points in the Late Holocene that the present, and could have influenced the myth of mermaids and mermen. A few fans have also theorised that the Mer's songs could have influenced the myths of Sirens as well.
This is the only marine mammal to appear in Primeval.
The commentary of Episode 2.4 mentioned that originally the sky in the Mer's home time period was going to be made red in post-production to make the future seem more peaceless.
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