Skip to content



Monoporeia affinis

Can you find something close by that feels cold? Or that feels warm? Does the tree bark feel warmer or colder than the ground?

The Monoporeia affinis is a small amphipod that measures up to about 8 mm. It enjoys the dark and avoids the light. It’s active during the night time but remains burrowed in the soft clay or sand of the seafloor during the day.

The Monoporeia affinis spread to the Baltic Sea from the Northern Arctic Ocean. Species that originate from the Artic Ocean are called glacial relicts. The ice sheets melted when the glacial period ended. The earth’s crust was pushed down under the pressure of the ice and thus the Baltic Sea was connected to other seas. When the earth’s crust started to rise, blocking the Baltic Sea from the Arctic Ocean, the Monoporeia affinis and other glacial relicts remained in the Baltic Sea. The water of the Baltic Sea is warmer and has lower salinity than the water of the Arctic Ocean. As time passed, the relicts from the Arctic Ocean have adapted to the different conditions of the Baltic Sea. Other glacial relicts of the Arctic Ocean are for example the Saduria entomon and the Baltic ringed seal.