The Mer Creatures were aquatic primates from the future that resembled seal-like apes.
Mer Creatures were around 4.5 metres long and 2 metres tall, with a large, seal/walrus-like tail for swimming, and a primate-like face and torso, seal-like tusks, and large fins in place of hands on their arms. Their skulls bore a resemblance to baboons. The Mer's skin was speckled dark grey with a lighter underbelly, with green down their backs. The Mer Queen was different from its smaller kindred in that it was around 11 metres long and 5 metres tall, it was covered in blubber and red markings (particularly down its back), and it had a slightly different-shaped and more bullish-looking head with extremely long lower tusks.
Mer Creatures, as with seals, apparently ate fish, as the Mer in the Creature Prison were given fish to eat. (Episode 2.7) However, they were apparently also willing to hunt and eat terrestrial animals as large as humans. Mer Creatures were also known to shed large pieces of their skin and simply shrub it off, in a similar manner to seals and walruses.
The Mer appeared to have weak skulls, as Connor Temple and Lucien Hope were able to kill Mer Creatures, or at least knock them out, by dropping large rocks on their heads. (Episode 2.4) Despite this, one Mer Creature was seen to ram its head against a door in Oliver Leek's Creature Prison with no apparent damage done to it. (Episode 2.7)
The Mer displayed high levels of intelligence, they had the ability to 'sing' underwater like whales, presumably to communicate. The Mer Creatures were able to navigate through complex networks of underwater pipes, and they were also known to capture their prey and lock it up alive in their lair; presumably storing it as a way of preserving their food. The Mer Queen was even seen to forcefully herd a captive Abby Maitland in its home environment. (Episode 2.4)
Mer lived in large groups and numbers, often working together to launch attacks against highly capable threats, although when hunting for unsuspecting prey they could work alone. The Mer's habitat and social structure in their home was highly similar to that of seals, with the Mer Queens acting in a similar role to elephant seals. The Mer Queen would also, when charging to catch food, violently crush and shove away the smaller Mer Creatures around it, although it is unknown whether or not this was accidental. (Episode 2.4)
Incursions and encounters
Several Mer Creatures came through an Anomaly from a shoreline in their future home, into a London warehouse in the present. The Anomaly then closed behind the Mer seconds afterwards. Some of the 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 the Mer Creatures launched an attack 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 Mer's home 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 (or knock unconscious) 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 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.
- Though unconfirmed, there are speculative rumours that the Mer's home time period is 50 million years in the future.
- 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. The Mer also appear to be inspired by Priscanthropus submarinus from another book by Dougal Dixon Man After Man, which are aquatic descendants of humans in the future, similar to how Nick Cutter speculates that humans are the ancestors of the Mer.
- Nick's joking comment about the Mer being a possible descendant of humans was 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 than 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.
- The Mer is the only marine mammal to appear in the Primeval franchise.
- 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.
- Concept art of the Mer depicted them as being more Walrus-like in appearance.