It has the "Ikea" logo molded in to it and when separated, the top most hole becomes more of a hook. Seems like it's meant to separate so it can be reassembled around a rope maybe?
What is this thing I found in a small stream? It's about 13cm in length, has evenly spaced holes all the way round covering the upper half of the tube. One side seems to be sealed, the other is open. Hard to say whether it's hollow inside as a lot of sediment has built up