Yep , if its made of plastic that is indeed a big clue , at first glance I was thinking glass.....my guess as its plastic is , its probably an inexpensive unit and just clipped together , I would start by running a blade between the two parts , if it is just push fit it wont take much to separate the two halves , will be light weight and wont need much to hold it together.....looks old too me so take it easy when levering , that plastic might have gone brittle with age....