Selome Hailu When director Dean Fleischer-Camp and star Jenny Slate wrote and produced their viral 2010 short film “Marcel the Shell With Shoes On,” they created the title character (voiced by Slate) as simply as possible. The tiny creature was made from a real seashell, doll shoes, a spot of clay and a googly eye.Becky Van Cleve, head of puppet fabrication on the feature-length adaptation of the short, in theaters June 24 via A24, made sure Marcel was always in sight as she worked to get him ready for the big screen.“I kept him right on my desk in a case,” says Van Cleve, knowing the little guy needed to be made of stronger stuff for the long haul: Because real shells are slightly translucent, they don’t hold up to studio lights.