The plastic component in the seed black is mainly cuttlefish bone. Cuttlefish bone is the skeletal structure of cuttlefish, which has certain elasticity and flexibility and is suitable for making some plastic products. The head length of cuttlefish bone is about 3 mm, the length of wrist is similar, the suction cups of each wrist are similar in size, and the outer edge of horny ring has irregular blunt small teeth.