It’s a cute and very simple craft. I used this idea. Cut out a paper rectangle along the short edge of an A4 sheet, one third of the sheet’s length. Draw crab’s eyes (or octopus’ head) in the middle, and symmetrically two claws and 6 legs (or 8 tentacles for octopus). Cut out and glue the edges to make a cylinder. Put on a sheet of paper with legs up, bend them down and glue the edges. Draw or glue eyes and mouth. Here you are!
Template: click and print out